eastern great australirin seawaw · the author retaks ownershrp of the copyright in tûis thesis....
TRANSCRIPT
Determination of Major and Trace Elements in
Eastern Great Australirin Bight SeawaW
by Double - Focusing Inductively Coupled Plasma
Mass Spectrometry
EFROSYNI-MARIA SKORDAKI
A thesis submitted to the Oeparbnent of Gmlogical Sciences and
Geological Engineering in conformity with the requinments
for the degme of Mastar of Science
Queen's University
Kingston, Ontario, Canada
Sepdember, 200 t
Acquisitions and Acquiiions et Bibliographie SeNices senrices bibiiiraphiques
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This thesis pnsents the anaiysis of 17 trace elements (conservaüve, recyded and seavenged rnetals) and 4 major ekments in seawater sampks ftom the Eastern Great Australian B ~ h t (WB). The trace ebments indude: Mo, Pb, U, VI Cr, Mn. Fe, Co, Ni, Cd, Al, Cs, Ba, Cu, Zn, Rb, and Li. The major elements indude: Na. Mg, S, and Ca
The methad used was a di&. muiü-element seawater analysis by a Doubk Foaising IridudRrely Coupled Plasma Mass Spectrometer. Only one intemal standard, indium (In), was used and quantification was obtained by matrix-adjusted extemal calibraüon*
Analysis for Na, Mg, Ca. S, Mo, U, Cs, Rb, Ba, V, Cr and Mn, demonstrated precisions (la) bwer than 10% daüv8 standard deviabn (RSD). with the exception of Cr (16% RSD) and V (14% RSD). The andytical muits shaiwed gaod agreement (within 95% confidence Iimit) with National Research Couneil (NRC) certif~ied referenœ materials (NASS-5, CASS-3 and SEW-2).
The combination of oceanographical and andytical information ftom the area of study (Eastem GA6) i n d i i ttiat îhere is a wami, hiihly &ne surface water body that ocaipies the centrd GAB area and maves eastward. This water mass mers the suthce iayw and can be traced to a distance of appmimatsly 250 iun from the cuast. Prailes of the major eiemsiits retkd the enhanead siaiinity levels of the central GAB su- waier, A CM. nutrient rich water flows underneath the warm surface of the GA8 seawater and rsaches shalaw deplhs in coaW a m . fhis water originates h m the Southem 0- airrent syskm and infiwnœs the nutrient contents of aie Eastern GA8 watsr. Tha hydrdogii and anaiyticai data for the a m of study indi ie an intense veitical rnixing between surlace and iniemed'iate waters.
The data from tha GAB was cmpad to dsta from the Mdderranean Sea and the Norai Atlantic Oaan. The EasWn GA0 sufface watts has sirrutar temperature, salinity and nutrient leveis as the Medhmem Sea surface W. At inîemiedii depths, the Eastern GAB oceanogtaphy resemMes ttrat of the North Aifantic. Major dement conbnts in al1 three regions ara ccmiparabk, w h e m some trace element kvds in the Eastern GAB and the Medi inean Sea waters are hiiher than those in theNorlhAt&nfïcôœan.
who have always been my inspiation through their Iifelong thurst for knowledge
and self-irnprovement
ïhey taught me that
( in Ancient Greek, "bemg hamana meam
"lmlcing up, trying to reach higher" )
As with most endeavours, thanks are due to a number of people:
My supervisor, Dr TK. Kyser, whose devotion to the pursuit of knowledge has provideci me with an excellent example of a brilliant researcher, of a great teacher- 1 am proud to have been one of his students.
Dr Don ChipIey, for wallcing me through the mystique world of ICP-mass spedmmetry. Chips, thank you for ail the knowledge you have given me, for being there for me, every step of the way.
Ms Kerry Klassen, her smile and fnendship have always welcomed me m "our lab, downstaus n ...
Frimds who have supported me and have beamie a neu* hdy , thm& my (inteniational.. .) graduate student tife in Khgsbn, in CaMda
Last but not Ieast, I would like to thank mv Sikok, mv k t friend.
iii
Table of Condents
.. Abstract ................................................................................. *--.-.----..-.-----...-.Il
... ....................................................................................... Acknowiedgements III
.......................................................................................... Table of Contents iv List of Figures ...............................*..........*..*............................................... ---ix
................................................................................................. List of Tables xv ........................ ......................................... Notation ................... ..... ..... xvi
Chapter 1 - Introduction and Research Objectives 1.1 Introduction ............................................................................................. 1
1.2 Research 0ûjdves ............................................................................... 4
Chapter 2 - Regions of Internt 2.1 General ................................................................................................... 5
................................................................. 2.1.1 Geneml Characteristics 6
........................................................................... 2.2 Great Australian Bight. -7
2.2.1 General Oescnption ...................................................................... 7
2.2.2 G a y ........................................................................................ 9
2.2.3 Drainage ......................... ..... ................................................... 9 ...................................................... 2.2.4 Climate 1 O
..................................................................................... 2.2.5 Hydrology -1 O
............................................................................... 226 GAB Currents 1 O
..................................................................... 2.2.6.1 GA0 Plume 10
22.6.2 LeewiLeewin Current (LC) ........................................................ 1 1
2.26.3 South Austraiian Cunent(SAC) ....................................... 12
22.6.4 Flinders Currerit (FC) ....................................................... 13
2.2.7 Seasarari ................................................................................... 13
........................................................................... 2.2.8 Sampled Region 14
.......................................................................................... 23 lndian Ocean 15
...................................................................... 2.3.1 General Descn'ption 15
2.3.2 Gealogy ........................................................................................ 16
........................................................................................ 2.3.3 Crimate 16
2.3.4 H ydrology ...........................*......................................................... 17
................................................................................. 2.4 Mediterranean Sea 18
........................................................................................ 2.4.1 General 18
24.2 Geology ...................... ....... ................................................. 18
2.4.3 Drainage ................... ... ............................................................ 19
......................................................................................... 24.4 Clirnate 19
............................................. 2.4.5 Hydrolog y 20
2.4.6 Mediirranean Outffow ................................................................... 23 ............................................... 2.4.7 Temperature and Water Chemistry 23
2.5 North Atlantic Oœan ................................................. d
......................................................................................... 2.5.1 General 24
2.5.2 Gedogy ........................................................................................ 24
........................................................................................ 2.5.3 Climate -25
...................................................................................... 2.5.4 Hydrdogy 25
.........*............ ...................*............. 2.5.4.1 Surface Cumnts .. 25
2.5.4.2 Deep Currents ........... .. ................................................. 26
................................................................................. 2.5.5 Temperature 28
.......................................................................................... 25.6 Safinity 28
Chapter 3 . Oceon Chemisty
................................................................................................... 3.1 General 29
PART l
........................................................ 3.2 Ma* Glemerit General 30
............................................. 3.2. t Residence Times of Major Elements 30
3.3 T m W k General Description ........................................................... 32
3-81 RssidemTimesofTraceMetals ................................................ 33
................... 3.3.2 Metrtls with Conmative Behaviour ................... .. 34
.......................................... 3.3.3 Metals with Nutrient - Like Behaviour 36
3.3.4 Scavenged Metals ....................................................................... 42
PART Il
3.4 Seawater Analysis ................................................................................. -47
3.5 Summary ................................................ ,. ........................................... 52
3.6 Seawater Analysis in this Investigation ........................ ................... . S2
Chapter 4 . Meaiod of Analysis
4.1 General ................................................................................................... 54
..................................................................................... 4.2 Instrumentation 54
................................................................................... 4.2.1 Introduction 54
4.22 Choii of an ICP System ............................................................. 55
............................. 4.2.3 General Oescription of aie ICP-MS Instrument 56
............................ 4.23.1 Double-Focusing ICP-MS in Viis Study -58
................................................... 4.3 Methodolog y ..... ........ 60
4.3.1 Blanks ........................................................................................... 63
........................................ 4.3.2 Choice of Reagent for Sarnple Dilutions 63
4.4 Compensatiori for Interferences 64
4.4.1 Spedroscopic Interferences .......................................................... 64
................................................................. 4.4.2 Chernical Interferences 69
................................................... 4.4.2.1 Internai Standardisation 69
.................................. 4-4-22 M;rtmc-Adjustecl Exîemal Calhatbn 70
4.5 Detecüon Limits and Procedurai Blanks .................................................. 73
Chapter 5 . Resub
5.1 General ................................................................................................... 75
5.2 Analytical Summary ................................................................................ 75
5.3 Analyücal Resuits Iw Major Elements ..................................................... 76
5.4 Major Element Concentrations in the Eastern GAB Seawater ................. ï7
........... ......*...*......................... 5.5 AnalytÏcal Results for Trace Elements .. 81
5.6 Trace Element Concentrations in the Eastern GA0 Seawater ................ 90
Chapter 6 . Oiscussian of Rssub
6.1 General ............,,................................................................................... 96
6.2 Gerieral Discussion on Eastern GAB Oceanography .............................. 97
.............................................................................. 6.3 Nutrient Distributions 108
6.4 Inshore-Offshore Station Correlations .................................................... -111
................................. 6.5 Eastern GA6 General Oceanography . Summary -123
..................................................................... 6.6 Major Elements .......... .. -124
6.8 Generai Recyded Metal OistrÎbutions ..................................................... 132
6.9 Correlation Between Nuùients and Recycled Metals .............................. 136
............................................... 6.10 General Scavenged Metal Distributions -143
6.1 1 Description of Ail Stations 007-057 . Correlation with Recyded and Scavenging Metals ........................................................ -146
...................................................................... 6.1 1.1 Stations 007425 147
...................................................................... 6.1 1.2 Stations 032453 156
..................................................................... 6.1 1.3 Stations 054-057 -162
6.12 Comparison of the Eastem GAB with the M e d i n e a n Sea ............................................................... and the North Atlantic Oœan 165
................. 6.12.1 Oceariic and Medierranean Sea Residenœ fimes 165
6.123 Salinity Profiles in the Three Regions ....................................... 168
6-124 Nutrient Profiles in the Three Regions ............ tttttttttttttttttttttttt170
................................. 6.12.5 Trace Meta1 Levels in the Three Regions 171
6.126 Major Element Levels in the Three Regions ............................ 176
Chapter 7 . Conclusions and Recomrnendations
7-1 General ................................................................................................... 179
............................................................................................ 7.2 Conclusions 179
................................................................................. 7.3 Recommendations -183
Appendix 1 . Conservative Trace Element Distributions .................................................................. in Eastern GA0 (Li) 1-1
Appendix II - Recycleci Trace Ekments Distributions .............................................. in Eastern GA6 (Cd. Ni, Cu, Zn) 11-1
Appendix III - Scavenged Trace Ekments ........................................................ In Eastern GA6 (Pb, Al) 111-1
viii
List of Figures
Fiure 2-1
Figure 2.2
Figure 23
Figure 2.4
Fgure 2.5
Figure 2.6
Fylure 27
Figure 2.8
Fgure 3.1
Regions of Interest: Great Australian Bight. South Indian Ocean. Mediirranean Sea and the NoRh Atlantic Ocean ............................................................................ 5
Location of the Great Australian Bight (GA81 ............................. 7
The GA0 and of the S ~ b - ~ c a l Convergence Zone ................ 8
Main coastal currents in the GAB .............................................. 12
Map of the FR 02/98 Cmise in the Eastern Great AustraIian Kght ........................................................... 1 5
The Indian Ocean and its Major SurFace Currents ..................... 17
The Mediterranean Sea and its Main Currents ........................... 22
The Norai Atlantic Ocean and its Major Surface Currents .......... 27
Profife of mdyWenum (Mo) in seawater, showing its conmaüve befmviour ........................................................ -36
Figures 3.2 and 3.3 Profiles of Cadmium (Cd) and phosphate (PO41 in oceanic waters ......................................................... 38
Fiiures 3.4 and 3.5 Profiles of Barium (Ba) and dica (Si) in Aff antic oceanic waters- ............................................... 41
Fgure 3.6 Profile of aluminum (Al) in cxeanic waters ................................. 43
Figure 3.7 Profile of manganese (Mn) in North Atlantic ooeanic waters ...... 44
Figure 4.1 W-MS Instrument .................................................................... 57
Figure 4.2
Fgure 4.3
Figure 5.1
Figure 5.2
Figure 5.3
Fgure 5.4
Figure 6.1
Figure 6.2
Figure 6.3
Figure 6.4
Fgure 6.5
Figure 6.6
Fgure 6.7
Procedure for the analysis of the trace metals and the major elements ........... .... ...................................... 61
Mat&-Adjusted Extemal Calibration Diagram ............ .., ............. 72
CASS-3 Certified Values versus CASS-3 found values for Mo and U ............................................................................ 82
CASS-3 Certified Values versus CASS-3 found values for Ni, Cu, Cd, V, Zn and Cr ....................... ,.,, ................... 83
CASS-3 Certified Values versus CASS-3 found values for Co. Fe. Mn and Pb .............................................................. 83
Double-Focusing ICP-MS Response Curve ............................... 87
Map of the FR 03/98 Cruise in the Eastem Great Australian Bight in March-Apnl 1 998 ................................ 102
Diagram showing the variations of Temperature and Salinity with depth. within the Eastern part of the region of study ......... 103
Diagram showing the varhtions of Temperature and Salinity with depth, within the Central part of the region of s M y (and in the Sperioer GU@ ........................................................... 103
Temperature vs Salinity correlation for Eastern GA8 waters ....... 107
Phosphate concentrations of GA0 seawater ...........,,................. 108
Nitrate concentrations of GAB seawater .................................. -108
Silica concentrations of GAB seawater ..................................... 110
Figure 6.8 8 6.9 Temperature and salinity depth profiles at stations 050 to 053 ....................................................... 112
Fque 6.1 0 8 6.1 1 Temperature and saiïnity depth Qrofiles atstatioiis044 to049 ................................................... 113
Figure 6.12 & 6.13 Temperature and salinity depth profiles at stations 032 to 041 ........................................... .. 115
Figure 6.14 & 6.1 5 Temperature and salinity depth profiles atstations 017 to 025 ................................................... 116
Figure 6.16 & 6 . l ? Temperature and salinity depth profiles at stations 007 to 0 16 .................................................. -1 18
Figure 6.1 8 & 6.19 Temperature and salinity depth profiles ai sbtions 054 to 057 ................................................. 1 20
Figure 6.20 Phosphate depai profiles in surface waters at coastal and offshore stations .................. ..... ............ A
......... Figure 6.21 Na Concentrations with depth in Eastern GA0 seawater 125
Figure 6.22 Mg Concentrations with depth in Eastern GA0 seawater ......... 125
......... Figure 6.23 Ca Concentrations with depth in Eastern GA8 seawater 126
Figure 6.24 S Concentrations with depth in Eastern GA0 seawater ............ 126
Figure 6.25 Mo depth profile in Eastern GA0 .............................................. 129
Figue 6.26 U depth prafile in Eastern GA0 ................................................ 129
Figure 6.27 Cs depth mle in Eastern GA0 .............................................. 130
Figure 6.28 Rb depth profile in Eastern GA0 .............................................. 130
Figure 6.29 Ba depth profile in Eastern GA0 ............................................... 133
Figure 6.30 V depth profile in Eastern GAB ................................................ 135
Figure 6.31 Cr de@ profile in Eastern GA0 ............................................... 135
Figure 6.32 . 6-34 Correlations between Nutrient and Ba amtmts ................................... in waters at stations 010 and O 1 S 137
Figure 6.35 . 6.37 Correlatiotrs beîwwn Nutrierit and 8a contents in waters at stations 017 to 025 ..................................... 139
Figure 6.38 . 6.40 Comlations between Nutnent and Ba contents in waters at stations 032 to 039 ...................................... 140
Fgure 6.41 . 6-43 Correlations between Nutn-ent and Ba contents in waters at stations 044 to 051 ...................................... 141
................................ Figure 6.44 Mn depth profile in Eastern GA0 seawater 144
.............................. F ~ u r e 6.45 Co depth profile in Eastern GA0 seawater -145
Figure 6.46 Fe depth prbfile in Eastern GA6 seawater ................................ 145
Figure 6.47 Fenœ Diagram of the main water bodies in the Eastern GAB .................................................................. -148
. .....,. Figure 6.48 6.50 Nutrient depth pmfiles in waters at stations 007-01 6 150
Figure 6.51 . 6.52 Ba and Mn deQth profiles in waters at stations 007 to 016 ...................................................... 152
Figure 6.53 . 6.54 Ba and Mn depth profiles in waters ...................................................... at stations 01 7 to 025 155
. Fgure 6.55 6.57 Nutrient dqth profiles in waters at stations 032-053 ....... 157
Figure 6.58 . 6.59 Ba and Mn depth profiles in waters at stations 032 to 039 ...................................................... 5 8
Fgure 6.60 . 6.61 Ba and Mn depth profiles in waters at stations 044 to 049 ..................................................... -160
Figure 6.62 . 6.63 Ba and Mn depth profiles in waters at stations 050 to 053 ..................................................... 161
....... . Fgure 6.64 6.66 Nuûient depth profiles in watsrs at stations 054-057 163
Figure 6.67 . 6-68 Ba and Mn deqtti profaes in wters at statim 054 to OS7 ..................................................... 164
Fgure 6.69
Figure 6.7 f
Figure 6.72
Figure 6.73
Figure 6.74
Figure 6.75
Figure 6.76
Figure 6.77
Figure 6.78
Fgure 6.79
Temperature distributions fbr Northwwt Atlantic Oœan, the Western Med i i nean Sea and the area of Research (GAB) .......................................................... 169
Salinity distributions for Northwest Atlantic Oœan, the Western Medierranean Sea and the area of Research (GAB) .......................................................... 169
Nutrient Distribution of Phosphate in Northwest Atlantic Oœan, the Western Mediterranean Sea and the area of Research (GAB) ................................................................. -1 72
Nutrient Distribution of Nitrate in Northwest Atlantic Oœan, the Westem Mediitemnean Sea and the area of Research (WB) ................................................................. -1 72
Nutrient Distribution of Silicate in North- Atlantic Oœan, the Western Mediterranean Sea and the area of Research (GAB) .............. ,,., ............................................ 172
Cornparison between Eastern GAB and Northwest Atlantic trace elements in surface waters (0-200m) ................. 173
Cornparison between Eastern GAB and Nuithwest Atlantic trace elements in deep watem (200 - 1000m) ............. 173
Comparison between Eastern GA0 and Western Mediterranean trace elernent concentrations in surface waters (0-200 m) ..................................................... 174
Companson between Eastern GAB and Western Mediterranean trace element concentrations in surface watem (200 - 1000 m) ............................................. 1 74
Cornpanson between Eastern GA0 and Mediterranean Sea major element concentrations ............................................ 1 77
Cm- be-n Eastem GAB and Nodh Aüanüc Oœan major element concentrations ........................ 177
Figure 1.1. Vertical Dstniution of Li, including al1 stations.
Figures 11.1, 11.2, 11.3, 11.4 . Cd, Ni, Cu and Zn vertical distributions for al1 stations of the area of research.
Figures 111.1 and 111.2 Al and Pb vertical distributions for al1 stations in the area of study.
Kit of Tables
Table 1 -1 Elements of Interest ...................................................................... 2
Table 3.1 Mean Oceanic Concentrations and Residence Times of the Elements of Interest ................................................................ 34
Table 4.1 Pteferred isotopes of the major elements and ........................... trace elements of interest for HR-ICP-MS analysis 67
Table 4.2 Detecîion litnits and averaged Procedural Blank values for Major Elements and Trace Uements of Interest ................................ 74
Table 5.1 CASS-3, NASS-5 and HPSW analytical results for the major elements of interest .......................................................... ï7
Table 5.2 Anaiyticai resuits obtaineâ for the major elements of interest in the seawater sarnples from the Eastem Great Aw'Jaliin BigM .................... .... ............................... 78
Table 5.3 CASS-3, NASS-5 and SLEW-2 analytical results of the trace elements of interest ........................................................................... 88
Table 5.4 Analyücal Resuits for the trace eiements of interest in the seawater samples fmm the Eastern Great Australian Bight .................................................................................................. 92
Table 5.5 Recyded and scavenged metal mean mcentrations measured in sampks frm sutface and intermediate
...................... seawater layers of the Eastern Great Australian Bight 95
Table 6.1 Descn'ption of 63 seawaW samples wliected in the region of study ............................................................................. 98
Table 6.2 Temperature and depth iRfwmation from Norttiwestern Atlantic Ocean, Western Mediterranean Sea and
......................................................... Eastern Great Australian Bight 167
Table 6.4 Nutrient and depth i n i h w b n fnnn NorttniiRstem Atlantic Ocean, Western Mediterranean Sea and Eastern Great Australian Bight ................................................... 1 71
AAS Atomic absorption spedmmpy
AES Atomic emission spectmscopy
ASW Atbntic Surface Water
CASS Coastal Atlantic SurFaœ Seawater
EMDW Eastern Meditenanean Deep Water
EfV Electrothermal Vaporisation
FC Fiinders Current
GA0 Eastem Great Australan Bight
HPSW High Punty Seawater
HR-ICP-MS High Resolution lndudively Coupled Plasma Mass Spectrometer
ICP-MS Indudively Coupled Plasma Mass Spectrometer
LC Leeuwin Current
LW Levantine Intemiedi Waters
MR Medium Resolution
NASS North Athntk Surface Seawater
NAW North Atlanüc Water
Q-ICP-MS Quadrupde ICP-MS
RSD Reiative Standard Deviation
SAC South Australian Cunerit
SLEW St Lawrence Estuanne Water
SST Sea Surface Tempemtm
CHAPTER 1
Introduction & Research Objectives
l .l Introduction
Major advances in the knowledge of the concentrations and distributions
of trace metals and major elements in the seas and oceans have occuned since
the mid 1970s. With the improved information on the true variations in the manne
chemistry, many systematic features in the demental distributions have become
apparent.
Information on the manne chernistty of trace metals and major elements is
of great importance because these elements play indispensable roles in the
natural ecosystem. Trace elements, such as lead, cadmium, zinc, manganese
and copper are invdved in air-sea interactions, ceII growth and maintenance of
metabolic functions in sea biota. Major eiernent concentrations, on the other
hand, are significarit indiators uf the &nRy levels in seawater as well as
regional dimatic vanatioris. - -
Accurate data on the distributions of trace rnetals in the marine
enviroiment are esenhl in understanding their efféd in various biogeochemical
and geachemical systems. However, analytical procedures for detemination of
metals in seawater impose limitations on obtaining this information,
Preconœntration techniques, that have been traditionally in use, are slow
because they require extensive laboratory preparations. Further, they deal with
low analyte concentrations and significant interferences from the complex
chernical composition of seawater-
Direct determination of trace elements in seawater reduces both the time
of analysis and contamination nsk h m long iaboratory procedures. The current
study demonstrates a direct, muîü-element, rapid analysis of seawater using a
high resolution inductively coupleci plasma rnass spectmmeter (HR-ICPMS). A
suite of 17 trace metals and four major eiements (Table 1.1) were chosen for
analysis in seawater amples colleded from the Eastern Great Australian Bight
(GAB) in March 1998.
Table 1.1: EIments of Interest
Mo, Pb. U, V, Cr, Mn, Fe, Co, Ni,
Cd, Al, Cs, Ba, Cu, Zn, Rb, Li
In order to be able to invesbigate efemental behaviour in the marine
environment of the Great AusWlivl BQht, the trace elements that wre chosen
fw study bekmg to di i rent types of elements in the marine environment:
conservative* recyding and scavenging (as discussed in W o n 3.3)- Major
Na, Mg, S, Ca
elements were also included in this research in order to examine the variations in
salhity of the GA0 waters.
Apart from their oceanographical importance, the selected elements also
have an analytical interest as they are exceedingly dicult to determine fclr
several reasons. (Section 4.4.1). The scope of the analytical part of the current
study is to achieve a better comprehension of the problems as-ated with the
analysis of the selected trace metals.
The Great Australin BigM regional oceanography has been previously
investigated by various researchers (Rochford, 1 984; Roctiforcl, 1 986; Gerbach
et al., 1999, Hehfeld and Tomczak, 1999). However, l i e is known about the
trace element and major element concentrations in this manne environment. This
work d-bes the profiles of 17 trace metals and four major elements and it
discusses the relation between the elemental behaviour and the oceanography of
the area. The findings of this wwk in the Great Australian Bight are ampared
with tvm welldocumented regiocis, the Meditenanean Sea and the North Atlantic
Ocean.
1 2 Research Objectives
The aim of this research project is:
To determine the concentrations of 17 trace elements (Mo, Pb, U, V, Cr,
Mn, Fe, Co, Ni, Cd, Al, Cs, Ba, Cu, Zn, Rb and Li ) and 4 major elements
(Na, Mg, S, Ca) in the Great Australian Bight seawater, using
Double-Focusing lndudively Coupled Plasma Mass Spedrometry.
To expfain the correlations between the trace element distributions and
the various parameters that affect the oceanography of the Great
Australian Bight.
To explore the differences and the sirnilarities of trace eIement
concentrations in the GA6 with other marine ecosysterns, nameiy, the
Mediterranean Sea and the North Atlantic Ocean.
CHAPTER 2
Regions of lnterest
2.1 General
This Chapter indudes a description of the oceanography of the Great
Australian Bight (GAB), the oceanic region where seawater samples of this study
were collected. Because the Great Austmlian Bight is a small part of the Indian
Ocean, the lndian Ocean is also examined. As dixusseci in Chapter #1, GAB
oceanic chemistry is compared to that of the Mediterranean and the North
Atlantic wiai respect to their general charaderistics Thus, the Mediterranean and
the North Atlantic environments are also topics within this Chapter (Figure 2.1).
Figure 2.1 Regions of interest, in this study, include the Great Australian Bight, part of the South lndian Ocean, the Mediterranean Sea and the North Atlantic Ocean.
2.1.1 General Characteristics
Environmental and geochemical parameters play an important role in
seawater composition, especially the concentrations of major elements and trace
metals. For this reason, the GAB, Mediterranean and North Atlantic regions are
examined for specific features that can provide a better comprehension of the
interrelations between the elements of interest and the marine environment The
lndian Ocean region, as the surrounding environment of GAB, is seen under a
more general prisma.
The GAB, Mediterranean and North Atlantic regions are studied with
respect to the following charactenstics:
a. Hydrology of the region, Mich is defined by water currents that
circulate in the area. These water bodies have diierent temperatures
and salinities. These parameters can help with the interpretation of the
analytical results of this thesis, given that distinct water masses of the
GAB region are defined by these. These two factors are also important
for the cornparison arnong GAB, Mediterranean and North Atlantic
oceanic environments.
b. Drainage of the area, which is a notable factor because it describes
the river input and allows the study of the river-seawater interactions.
Information on freshwater discharge can provide a basis for explaining
major elements and trace metals concentrations on a local scale.
c. Cilmatic conditions of each region, which is a significant factor
because it can affect the temperature of the surfa- seawater layer,
wind-driven water bodies, as well as affect evaporation and
predpitation rates in the region. Climate also influences seasonal
in salinity results in a concomitant increase in the concentrations of the
major seawater caüons.
d. Geological evolution, which describes the geological setting of each
region and the sediments that exist in the area. The riesulting elemental
concentrations in seawater can be ascertained from the formation of
the physical environment, the type of sediments, and the seawater-
rock reactions.
2.2 Great Australian Bight
2.2.1 General Description
The Great Australian Bight is a wide embayment of the Indian Ocean bordering on southem Australia (Figure 2.2).
Figure 2.2 Location of the Great Australian Bight (GAB).
The region of the Bight, wtiich is the largest smor of southern Australia, extends
e a M fmm Cape Pasley, Western Australia, to Cape Carnot, South Australia,
a distance of 1,160 km (Longhurst, 1998). The Great Australian Bight is a latitude-paralfel shelf, 500 km north of the Suùtmpical Convergence Zone
(Figure 2.3) and has relatively shallow waters (Herzfield and Tomczak, 1999:
James et al., 2001). The Subtropical Convergence Zone, at about 40' south,
generally defines the northem iimit of a water m a s having unique biological and
physical characteristics mat it is often given a separate name, the Southem
Figure 2.3 The GAB is iocated 500krn north of the Subtropical Convergence Zone.
The Great Australian Bight was first visited in 1627 by the Dutch navigator
Pieter Nuyts. The bmen aast was surveyed by Matthew Flinders, an
Englishrnan, in 1802 (Longhurst, 4998).
The Great Australian Bight was formed by the separation of Australia from
Antarctica during the Cretaceous period and obtained its present configuration by
the subsequent northward drift of the Australian continent (Thompson and Turk,
1993). Southem Australia has several shallaw embayments filled with Cenozoic
mol-water limestone and minor sandstone (James et al., 2001). The limestones
are deep-shelf, bryozoan-rich and dolornitized. Generally, the GA8 is an
extended carbonate platforni (apprmimately 260,000 km2) afïected by
subtropicat, aRd conditions. lt is the largest region of temperate, cool-water,
heterozoan limestone deposition in the modem world. Environments of
deposition range from wam-temperate regions inshore to ml-temperate regions
offshore (James et al., 2001).
2.23 Drainage
South Australia is notably deficient in Wers (Longhurst, 1998). The Murray
River is the oniy large permanent river, Oowing 2,589 km across southeastem
Australia to the Great Australian BigM Although it has a total catchment area of
1.O72,W km2, its average annual discharge is only 0.89 m3 l S. and it has dried
up on at teast three occasions (Longhurst, 1998)
2,2.4 Climate
The Great Australian Bight is part of South Australia and is the driest of
the Australian States. The southem coastal zone has been characterird as
having a "Mediterranean" climate with mild-to-cool, wet winters and hot, dry
summers (Longhurst, 1998).
2.2.5 Hydrology
The eaastat boundary of the southem coast of Australia, between Cape
Leeuwin in the west and Tasmania in the east, is under the infiuenœ of three
major water masses (Figure 2.4) that ocair for al1 or part of the year within the
sheIf and slope region off southern Australia (Rodrford, 1986). These water
masses consist of the GAB Plume, the two wastal cunents (LeeuWin Current
(LC) and South Australian Current (SAC)) and the Flinders Current (FC)
(Rochford, 1986). These water bodies are described below-
2.2.6.1 GAB Plume
This is a wam water mass with very high salinity and is present in the
cemal and eastm half of the Great Australian BigM for most of the year
(RoeMord. 1966; Heraield and Tomczak, 1999). It can be desaibed as a zone
of nutrient - depleted surface seawater temperature up to 23OC along the
northwest sheif (James et al., 2001). This water body exhibits safinities that
commonly exceed 36OIm (Hefzfield and Tomczak, 1999).
2.2.6.2 Leeuwin Current (LC)
The source waters for the Leeuwin Current are off Australia's northwest
coast, where a mass of warrn (-19°C), low-salinity water (35.8-35.9 is
formed by the seasonal flow through the Indonesian archipelago (Rochford,
1984; Longhurst, 1998). This surface water body then travels southwards into
the Leeuwin flow and proceeds eastwards along the southern Australian shelf
(Figures 2.2 and 2.4). It is important to note that the dynamics of this eastern
boundary current along the western Australian coast, known as the Leeuwh
Current, are very unusual (Rochford, 1984). Unlike al1 other eastern boundary
currents, LC flows polewards, not equatorwards, despite the equatorward wind
stress over the eastem lndian Ocean and the general equatorward flow in the
eastem limb of the subtropical gyre further offshore (Longhurst, 1998). The
Leeuwin Curent is a surface flow of warm water that flows at relatively high
velocity (0.1-1.4 mls) above an equatorward underwmnt, with the level of no
motion between the two flows being approxirnately 200-300 m (Gersbach et al.,
1999). As described in Section 2.2.7, the LC demonstrates a seasonal
charader that is due to changes in local wind stress (Smith et al., t991).
The LC follows the shelf break of the GAB as far as and reaches its
maximum in austral winter, from May to Odober (RocMord. 1 s ) . ln austral
spring (September-December) the Cunent weakens. reaching its weakest point
in early austral summer, in January (Rochford, 1986).
The LC is responsible for the warm and saline surface water mass which
ocaipies the central and eastem part of the BigM during much of the year
(Rochford, 1986; Longhurst, 1998). However, this water mass is modified by the
arid and evaporative nature of the cuastal dimatic regirne (Figure 2.4).
Cunent
Flinders Current
Figure 2.4 The main coastal currents that appear in the GAB region are the Leeuwin C u m t and the South Australian Current (SAC). f he Southern Ocean originating Flinders Current also affects the area.
2.2.6.3 South Austnlian Curient (SAC)
The South Austraiiin C u m t water topagraphicalIy appears in the east of
the Great Australian Bight (Figum 2.4). This c u m t is formed by warm, saline
waters generated during summer months in the BigM and flows eastward
(RocMord, 1986; James et aL, 2001 j.
2.2.6.4 Flinders Current (FC)
The Flinders Current water is cdd, oxygen and nutrient rich. It is part of
the west wind drift of the Southern Ocean curent system (Millero and Sohn,
1992; Longhurst, 1998). Spedkafly, the FC originates from a deep oœan
circulation water mass (Antardic Intemediate Water) that moves northward and,
as approaches the Great Australian 8igM coast, moves westward (Gerbach et
al., 1999). This curent dows beneath the South Australian Current and the
Ceeuwin Current (Figures 2.4). During austral summer rnonths (January -
Febniary), the FC can flood onto the cuntinental shelf following the slackening of
the Leeuwin Current (Henfeld and Torncmk, 1999).
2.2.7 Seasonality
The water masses in the area of the Great Australian Bight are greatly
influenced by seasonality ( H d l d and Tomctak, 1999). During austral
springüme, the water masses on the sheff have a sea surface temperature (SST)
of around 17"C (Longhurst, 1998; James et al., 2001). Contined heating through
austral summer months mates the GAB Plume. In mid-summer, this water mass
can be traced on the east shelf, as weK During the same penod, eoastal
upwelling occurs on the eastern part of ttbe Bight allowing cold water (amund 1 O-
14OC) to corne ta the su- (James et al., 2001).
As fall approacties. air temperatures decrease and the northwest coastaI
waters begin to cool (RodrfOrd, 1986). The Great Australian Plume continues to
appear on the eastern sheIf but becornes cooler, as well. Around this time, the
LeeWn Current intnides into the GAB from the west coast, starting ta become
dominant and, by the end of th& season, begins to mix with the GAB plume
(Rtxhford, 1 986).
ln austral winter, as the coastaf waters temperatures decrease even more,
the GAB Plume flm eastward, but separates h m the mast (Rochford, 1986).
The Leeuwin Cumnt joins the GA6 Plume and forms a warm water mass which
is charaderised by tM, main cumnts: the Leeuwin Current and ttie South
Australian Current (James et al., 2001). This carnbined water mass covers the
entire outer rnargin of the shelf and is much warmer than the coastal waters
(Figure 2.4). The LeeuWin Current is n w at its maximal strength and prevents
the cdd Flinders Current waters fmm reaching the sheR (Longhurst, 1998). As
the water temperatures along the coast continue to drop, the warm water mass
fbws away from the shelf (James et al.. 2001). As winter progresses, the GAB
achieves un îfom temperature, before aie heating phenomena of springtime
appear again (James et al., 2001).
2.2.8 Sampled Reg ion
Sixty thme water samples were anatyzed in this study. All of these
sampks were colleded from the eastem toast of the Great Australiin Bight
during an oceanographic mise on the CSlRO research vesse1 H.M.S. Franklin
during March and April, 1998 (Figure 2.5)- The sampled region (stations 007-
057) expands fian 139 OE to 130 O€, except for samples (SVVT) 054, 055, 056,
057, which were dieded from the Spericer Gulf. Sample charaderistics, such
as de@, nutrient contents and temperaturesalinity variations were determined
14
on-board the H.M.S. Franklin. The sample depths range between surface water
bodies (0-200m) and intemediate water masses (200-991 m). Sample locations,
depth, water temperature, salinity and nutrients (nitrate, silica. phosphate) are
presented in Table 6.1.
Figum 2.5 Map of the FR 03/98 Cruise in the Eastern Great Australian Bight in March-April 1998. The arraws indicate the direction of the cruise. The location and the number of each station ( h m 007 to 057) is rnarked on the cruise line.
2.3 lndian Ocean
2.3.1 Geneal Description
The lndian Ocean, north of the Subtropical Convergence zone, covers
approxirnately one-fifth of the total ocean area of the worid (Figure 2.1). It
stretcties for more than 10,000krn between the southern tips of Afiica and
15
Australia and, without its marginal seas, has an are8 of about 73,440,000 km2
(Longhurst, 1998). The average depth of the lndian Ocean is 3,890m. One of the
large gulfs of the lndian Ocean is the Great Australian Bight, off the southem
coast of Australia (Figures 2.2 and 2.6).
2.3.2 Geology
The origin and evolution of the Indian Ocean was the resuIt of the breakup
of the southem supercontinent Gondwanaland about 150 million years ago
(Thompson and Turk, 1993). By 36 million years ago, the lndian Ocean had
taken on its present configuration (Figure 2.6). Althwgh it first opened some 125
million years ago, almost al1 the Indian Ocean basin is less than 80 million years
old (Longhurst, 1998).
2.3.3 Climate
The Indian Ocean can be subdivided into four generak latitudinal dimatic
zones based on atrnospheric circulation: the Monwon Zone, the Trade-Winds
Zone, the Subtropical-Temperate Zone and the Subantarctic-Antarctic Zone
(Thornpson and Tu&, 1993). The GAB belongs in aie Subtropical region, which
lies in the subtropical and temperate latitudes of the Southem Hemisphere,
between 30% and G0S. In the northem part of this zone, the prevailing winds
are Iight and variable (Longhurst, 1998). In the çouthern area, the prevailing
winds are moderate to strong westefiy winds. The average air temperature
decreases with increasing southern latitude: from 22% down Co 10°C in the
Austral sumrner (December to Fekuary) and from 17% to 6% in winter
(Longhurst, 1998).
2.3.4 Hydrology
Major surface currents in the Indian Ocean fom a gyre that consists of the
South Equatorial Current, the West Australian Curent and the Agulhas Current
(Figure 2.6). Since this is mainly a southem hemisphere ocean, the currents
move to the left of the wind direction, and the abovementioned gyre rotates
counterciockwise (Kennish, 1994; Duxbury, 1 996). In the northem hemisphere
portion of the lndian Oœan region, northeast trade winds drive the North
Equatorial Curent to the west (Figure 2.6). The coastal Leeuwin Current also
appears in the area, flowing polewards and intniding the Great Australian Bight
marine environment.
Figure 26 The Indian Ocean and its major surface currents
2.4 Mediterranean Sea
2.4.1 General
The Mediterranean, the cradle of Western Civilization, is a marine
environment surrounded by land and is almost an enclosed sea. It lies between
latitudes 30°N and 46ON and longitudes S050' W and 36OE. It is surrounded by
Europe, Asia and Africa and is included in the Atlantic oceanic basin.
2.4.2 Geology
Until the 1960s, the Mediterranean was thought to be the main existing
remnant of the Tethys Sea, which formerly girdled the Eastern Hemisphere
(McGeary et al., 2001). Studies of seafloor spreading undertaken since the
1970s, however, suggest that the present Mediterranean seafloor is not part of
the older (200 million years) Tethys floor (McGeary et al., 2001). The structure
and present forrn of this tectonically active basin and its bordering mountain
system have been determined by the convergence and recession of the relatively
stable continental plates of Eurasia and Aftica during the past 44 million years
(Thompson and Turk, 1993). There are, at present, at least six main areas of
collision between Afnca and Eurasia, resulting in volcanism, mountain building,
and land submergence (Leondaris, 1992). Recent studies indicate that the
Mediterranean Sea shrinks at a constant rate while the Afn'can tedonic plate
moves northwards. sinking under the European tectonic plate (Thompson and
Turk, 1993). Frequent earthquakes and the active volcanism in the region show
that the geology of the Mediterranean Sea is still developing (Leondans, 1992).
The length of the Mediterranean Sea, along the 38'" parallel, is about
3800 km and the width of this sea is 1800 km (Papanikolaou and Sideris, 1988).
The Mediterranean Sea is divided into two parts, a western and an eastem part
(Figure 2.7). The boundary is naturally drawn by the presence of sills (submarine
ridges at 500m depth) at the Straits of Sicily, between southern ltaly and Tunisia
(Malanotte-Rinoli and Hecht, 1988; Saager et al., 1993).
The Western Basin of the Mediterranean Sea has depths greater than
1OOOm and covers a 563 x 1 d km2 area. The Eastern Basin ocaipies a 1405 x
1 O' km2 area and has depths greater than 1000m (Gabrielides, 1996).
2.4.3 Drainage
The Mediterranean Sea receives only about one third of the amount of
water that it loses by evaporation from the rivers that flow into the Sea
(Emelyanov and Shimcus, 1986; Hemt et al., 1999). As a mnsequence, there is
a continuous inflow of surface water from the Atlantic Oœan. A small amount of
water also enters the Mediterranean fram the Black Sea as a surface current
(Boyle et al., 1985).
2.4.4 Climate
The region belongs to the sub-tropicâl zone (Longhurst, 1998). Airfiow into
the Mediterranean Sea is through gaps in the mountain ranges. These strong
winds -known locally as "mistraP, "levanter", 'siroccon- lead to the reduction of
heat and moisture in the surface waters by a signifiant degree thrwgh
evaporative cooling (Longhurst, 1998). The resulting colder. denser surface
water then sinks. Atrnospheric conditions over the Mediterranean also increase
the salinity of inming Atlantic water because of evaporatian of surface waters
(Boyle et al., 1985).
The Mediterranean summer is hot and dry and the winter is mild and
tturnid (Longhurst, 1998). The lowest water temperature on the sea surface is
observed in January (+a°C) in aie Noraiern part of the Adriatic sea and the
highest (+30°C) occurs in August in the NorthEastern part of the Levantine Sea
(Emelyanov and Shimcus, 1986). Precipitation in the northem part of the
Mediterranean region is high (500-100Q mm a year), Mile in the southern part it
demases to a minimum of less than 30 mm per year (Emelyanov and Shimcus,
19s) . The evaporation mean value for the Mediterranean environment is
estirnated to be 125 cm per year. As a result of this, the salinity of the
Mediterranean seawatet can mach levels as high as 37.3% - 4 0 ~ 1 ~ (Malanotte-
Rinoli and Hecht, 1988; Bethoux et al., 1990).
Then are three well defined water masses that play a crucial role in Vie
oceanography af the Western Elasin of the Mediterranean Sea (Figure 2.7):
The North Atlantic Water (NAW),
The Levantine Intermediate Waters (Lw, and
The Western Mediterranean Deep Water (Bryden and Stommel, 1982;
Saager et al., 1 993).
The NAW is identifiable at 3ûm depth and wnsists of a watw inass
coming from the Straits of Gibraltar. The progression of the Atlantic slrface water
cm ùe followed by the salinity minimum in the Mediterranean Seawafeï, thrwgh
the Gibraltar Strait and Aiboran Sea, toward the North - Western Basin or the
Eastern Basin (Ruiz - Pino D.P. et al., 1991). The L W originates from the
Eastern Basin and fiows in the Western Basin through the Sicilian Channel. It lies
within 400 and 600 rn in depth. The Western Mediterranean Deep Water
extends underneath the LW. At ca. 1000 m depth, the water reaches
temperatures as Iow as 15-1 3OC (Rivaro et al., 1998).
Seasonality affects these water masses. Specifically, winter phenornena
cause a mking of different water masses so that a homogeneous layer is
produced at 200m depth allowing the LIW to ocair between 200 and 600m depth
(Rivaro et al., 1998).
The Eastern Mediterranean Basin, as in the Western Mediterranean
Basin, has three water masses that can be identifid, namely, the Atlantic
Surfaœ Water, the Levantine Intmediate W a t ~ and the Eastern Mediterranean
Deep Water. At the surface, Atlantic Surface Water (ASW) penetrates as far as
the eastemmost Mediterranean (Saager et al., 1993). Due to extensive heating of
surface waters during summer, a Iid of warrn water is fonned, preventing early
dissipation of ASW in the Western Mediterranean. In winter, the ASW cm no
longer be identifid east of the Straits of Sicily (where the natural bam'er between
the hlK1 b8Sins is). Saager et al. (1993) report that the salinity of these waters
varies betiriRen 38-4°!m to 38.@lo0. The ASW extends between 20 and 50m depth
and immediately below, the Levantine Intmediate Water (LW) extends
between 60 and 40e600m depth and generally flows westward (Measures and
Edmond, 1988). LW is charaderized by a maximum salinity of 38.9°1~ -39.l0lm
at 80 -200 m depth (Measures and Edmond, 1988).
Figure 2.7 The Mediterranean Sea and its main currents (1. Mediterranean Outfiow, 2. North Atlantic Surface Water, 3. Levantine Intemiediate Water). The Straits of Sicily (4) divide the Mediterranean Sea into the Eastern and the Western basin.
Beiow 600m depth, Mediterranean Oeep Water is present with a
temperature of 13.6'~ and salinity of 38.66'1~ (Measures and Edmond, 1988;
Van der Weijden et al., 1990) This water mass is called Eastern Meditenanean
Deep Water (EMDW). Due to the existence of a natural bamer at the Strait of
Sicily, there is no exchange of watet between the deep western Mediterranean
and the deep eastm Mediterranean (Brydeci and Stommel, 1982).
The formation areas as welI as the general flow direction of the
Mediterranean deep water mass have not yet been defined (Saager et al., 1993).
Deep water residence times are esümated to be arwnd 100 years (Laumont et
al., 1984; Saager et al., 1993).
2.4.6 Mediterranean Outfîow
There is a deep oufflow of denser Mediterranean water through the Strait
of Gibraltar (Figure 2.7). Bryden and Stommel (1982) suggest that this
outflowing water is made up of two types of water, Levantine Intermediate Water
and Western Mediterranean ûeep Water. This curent is at 400m depth. The
transport of this outflow is edrnated to be comparable with its formation rate,
resulting in a direct exodus of the deep water h m the western Mediterranean
basin (Bryden and Stomrnel, 1982; Boyle et al., 1985; Statham et al., 1985;
Measures and Edmond, 1988).
2.4.7 Temperature and Water Chemistry
In the Mediterranean Sea, in general, the water temperature decreases
with depth: 13-17.5°C in the 200 rn layer, 12-14.3"C in the 1000m layer and 12.6-
l4.2C in the 2000m layer (Ernelyanov and Shimcus, 1986). However, it remains
high near the bottom in all the deep water areas of the Mediterranean Sea, up to
1 2.ï°C in the Western Basin and up to 14OC in the Eastem Basin.
The salinity of the Meâïderranean Sea is uiifomiiy high throughout the
region (Boyle et al-, 1985). Surface waters avefqe atmt &lm. However, the
salinity can appoad 4 0 ~ 1 ~ in the eastem Mediterranean dunng the summer.
Deepwater average salhity value is 38.4Olm or slightly less (Emelyanov and
Shimcus, 1986). Vertically, the salinity first decreases because of the Atiantic
water idiow, then inueases, reaching its maximum in the 25û-500m layer
(Emelyanov and Shimcus, 1986; Saager et ai., 1993). Sinking of the more saline
Levantine waters and their spread westwards at depths of 250m to 500m are
responsible for the appearance of the salinity maximum at such depths
(Emelyanov and Shimcus, 1986; Rivaro et al., 1998).
2.5 North Atlantic Ocean
2.5.1 General
The Atlantic Ocean is the youngest of the oceans and the second-iargest
individual ocean on the planet, spanning a surface area of approximateiy
81,630,000 km2. It has an average depth of approximately 3,330 m (Thompson
and Turk, 1993). The North Atiantic is rich in islands, in the variety of its
coastline, and in tributary seas, inciuding the Mediterranean Sea (Figure 2.1 and
28).
2.5.2 Geology
The North Atlantic Ocean f m e d as a result of tedonic activity
(Thompson and Turk, 1993). These tectonics movements led to the
development of the Mid-Atlantic Ridge, The Mid-Atlantic Ridge, which sbetet#s
the length of the Atlantic Ocean, separateci the North Amencan Continent fr#n
Europe during the Jurassic peflod of the Mesozoic era (Papanikolaou and
Sideris, 1988). As the seafiaor continued to spread, South Arnerica separated
from Afn'ca during the Cretaceous period. Water filled the gaps creating the
çontemporary ocean. This spreading is developing today at a rate of a less than
2.5 cm per year (Thornpson and Turk, 1993).
2.5.3 Climate
Weather over the North Atlantic is largely detemined by large-scale wind
currents and air masses emanating from North America. ln certain regions, wave
cyclones (low-pressure areas) are formed. These weather phenomena occur at
zones of large temperature contrasts between the polar outbreaks and wamer
air masses. The growth rate of the cyclones depends largely on the temperature
wntrast, so that storms in winter usually are stronger than those in sumrner
(Duxbury, 1989; Longhurst, 1998).
2.5.4 Hydrology
Since the North Atlantic Ocean is a narrow, confined ocean of relatively
small volume but great north-south extent, the water types are readily identifiable
and their movement can be followed quite easily. The bardering nations of the
North Atlantic have had a longstanding interest in oceanagraphy. As a result,
th8 vertical circulation and layering of the Atlantic are both the most studied and
the best understood of al1 the oceans (Longhurst, 1998).
2.5.4.1 Surface Cumnts
The svface anents of the Atlantic Ocean primarily correspond to the
system of prevailing winds with such modifications as are imposed upon the
movement of the water by land boundaries (Dwbury, 1989). There is a large-
scale cirwlar movement of surface currents in the North Atlantic (Figure 2.8).
This gyre is formed by the North Equatorial Current, which fi ows west. It is forced
by the North Amencan continent to flow northeast along the coast of North
America as the Gulf Stream Current. This wann current continues to the east
toward northern Europe as the North Atlantic Curent. A branch of the Gulf
Stream Current flows to the northeast, across the North Atlantic and onward
toward the Arctic Ocean. This warm and shallow current is the North Atlantic
Drift (Thompson and Turk, 1993).
As the North Atlantic Current reaches the European continent, it heads
southward and becomes the Canaries Current. This current fiows along the
European coastline and the west coast of northwestern Afiica. This water
continues westward across the southern part of the North Atlantic, as part of the
North Equatorial Current, cmplefing the circulation loop (Millero and Sohn,
1 992).
Cold, low-salinity water ffows south from the Arctic Ocean along the east
coast of Greenland as the East Greenland Current, wtiere it is gradually mixed
with warrner Atlantic water. This water continues northwest, along the Greenland
coastline and, after the addition of cold water, flaws south as the cold Labrador
Current (Duxbury, 1989).
2.5.4.2 Deep Currents
The deep and bottom water of the Nortti Atlantic, consists of surface water
that sinks betweeri 50 and 600 NI where it spreads to the south. Specifically, the
cold Labrador Current moves to the south of Newfoundland, where it meets the
warm waters of the Gulf Stream. In winter, the resulting mixed water, with a
salinity of almost 35'1~~ and a temperature of 3OC. attains a density high enaigh
to make it sink to the bottom and spread to the south. Similady, bottom -ter is
forrned in winter to the north of Iceiand, but this has a considerably lower
temperature, about -l°C (Millero and Sohn, 1992).
As well, at depths between 1,000 and 2,000 m, the Mediterranean Outfiow
spreads and forms an intermediate salinity maximum (Section 24.5). With
increasing distance from the Mediterranean, the salinity decreases because of
mixing with other water masses, but traces of Mediterranean water are found as
far south as latitude 40's. Further, the Antarctic Intemediate Water (Section
22.6.4) crosses the Equator and can be traœd to about 2O0N (Millero and Sohn,
1 992; Thompçon and Turk, 1993).
Figure 2.8 The North Atlantic Ocean and its major swface arrrerits. 1: Labrador Current, 2: East Greenland Current
2.5.5 Temperature
The distribution of the sea-surface temperature is doseIy related to the cfiaracter
of the currents. The region of high surface temperature is wide off ihe Arnerican
east coasts, under the influence of the wami Gulf Stream Current, but it is narrow
off the African coast, where the Canary Current cames wld water toward the
Equator. Further, at the conjunction of the Gulf Stream and the Labrador Current,
the surface temperature changes rapidly within a short distance and this interface
is known as "the wld wall." At greater depths in the North Atlantic, the
temperature decreases slowly toward the bottorn from a value of about SOC at
1,000 rn to about 2.5OC at the bottom (Millero and Sohn, 1992; Thompson and
Turk, 1993).
2.5.6 Salinity
The surface waters of the North Atlantic have a higher salinity than those
of any oüwr ocean. reaching values exœeding 37'1~ in latitudes 20' to 3@N.
The basic salinity value is at at 35.5 for the North Atlantc. These salinity
Ievels can be explained as the effect of the intense evaporation in the
Mediterranean and the outfiow from that sea of high-salintty water. In that way,
the salinity of the North Atlantic is maintained at a higher level !han any other
ocean (Millero and Sohn, 1992; Thompson and Turk, 1993).
CHAPTER 3
Ocean C hemistry
3.1 General
This Chapter provides background information on the manne chemistry
related to trace metals and major elements. Each of the 21 elements of interest
for this study are examined in detail, in order to gain a better understanding of
their geochemical relationships with respect to environmental parameters.
This Chapter is bmken dawn into two parts:
Part I will examine each of the major elements and trace metals
(included in this study) with respect to tesidence time and behaviour.
Part II will review the most ment analytical methods used in seawater
analysis by experts in the analytical marine geochemistry field, in order
ascertain the curent state of research on this subjed
PART 1
3.2 Major Element General Description
The major wmponents of seawater are defined as those which contribute
significantly to salinity (Riley and Skirraw, 1975; Kennish, 1994). This indicates
that these elements have cuncentrations of 1 mglkg (Le. 1 ppm) or greater.
These components are the cations of sodium (Na), potassium (K), calcium (Ca),
magnesium (Mg), and strontium (Sr), and the anions chloride (CI'), sulphate
(SOC), bmmide (Br), bicarbonate (HCOj). fluoride (F). and bonc acid (H2B03)
(Riley and Skinow, 1975). These major constituents are generally considered
wnservative in behaviour (Goldberg, 1975; Fumess and Rainbow, 1990). As
reported in the literature, the average values of the major elements in seawater
(at 35 'lm salinity levels) are : Na = 10773 ppm, Mg = 1294 ppm, S = 904ppm,
and Ca = 41 2 ppm (Riley and Skirrow, 1975; Millero and Sohn, 1992).
ln this study, sodium, magnesium, sulphur and calcium are measured in
seawater samples from Eastern Great Australian Bight. The aquired values are
compared with the average concentrations of ihe same elements in
Mediterranean seawater and North Atlantic oceanic water.
3.2.1 Residence Times of Major Elements
The average (or mean) time that a substance rernains in solution in
seawater is called its rssidence time (Mîitfield. 1979: Duxbury, 1989; Kennish,
1994). The midence time, r, can be defined as the average time which a
substance remains in seawater befbre removal by some precipitation or
adsorption proœss, and is given by.
Total Mass of the Element in Sea . - Mass suppiied per year
(Eq'n 3.1)
Major elements, such as sodium, potassium, sulphur and magnesium are
very soluble in seawater and have long mean oceanic residence time, on the
order of millions of yearç (Table 3.1). Calcium is an exception in the major
constituents group because it is less abundant in the sea as it is used to form the
shells of marine organisms and, thus, is removed rapidly from seawater. As a
result, the mean oceanic residenœ time for calcium is one million years
(8roecker and Peng, 1982; Riley and Chester, 1983; Duxbury, 1989; Millero and
Sohn, 1992).
Because the residence time of most of the major elements is long relative
to the mixing time of the oœan, the ratios of the concentrations of the major
elements are effectively constant. Minor elements, which have significantly
shorter residence times than the mixing of the ocean have variable
concentrations in seawater. Generally, elements that have short residenœ times
are more readive than those that have long residenœ times. The major
elernents, therefore, behave conservatively in seawater; their concentrations are
constant except at ocean boundaries where they are changed by input or output
processes. These processes indude anttuopogenic actMties. dilution by river
ninofi and precipitation ont0 the ocean surka (Riley and Ches&r. 1983; Milfero,
19%).
3.3 Trace Metals General Description
In general, the reasons for developing our knowledge of the oceans are to
obtain sources for food, chemicals and energy. At the same time, the oceans
wntrol the climate of the earth and are also a sink for industrial and radioactive
wastes (Broecker and Peng, 1982; Fumess and Rainbow, 1990; Millero and
Sohn, 1992; Huber, 1999). The study of the manne geochemistry of metals
allows us to obtain a better understanding of the interactions between trace
elements, their impact in the ocean and also to explore the chernical kinetics of
the oceanic environment. Trace metals in seawater are defined as minor
elements that occur at concentrations less than 1 mg/kg (i.e. 1 ppm) in seawater,
excluding nutrients, dissolved gases and radioactive elements (Wong et al.,
1983; Kennish, 1994). Many traœ metals are essential to life, such as iron (Fe),
copper (Cu) or zinc (Zn). These metals occur in low concentrations in organisms.
However, there are also non- essential traœ metals such as cadmium (Cd), gold
(Au), lead (Pb), mercury (Hg) and silver (Ag).
In this thesis projed, a series of selected trace metals (discussed in the
following sections) are examined in aie Great Australian Bight oceanic region
and further compared to Mediterranean seawater and North Atlantic waters.
These trace metals in the oceans fall into three principal categories, acmrding to
their type of distribution and their geoctiemical behaviour: Consemative,
Recycling (or Nutrient-like) and Scavenging metals.
3.3.1 Residence Times of Trace Metals
Generally, an element can have a low concentration in seawater for two
reasons: (1) it may be very reactive and thus be rapidly removed to he
sediments, and (2) it rnay occur in very low concentrations at its source, such as
crystalline rocks. For example, Al is one of the most predominant constituents of
igneous rocks; its high readivity in the marine environment reduces its
concentration and it has a relatively shoR residence time (Table 3.1). The
element Cs, on the other hand, has a Iow concentration in seawater, in aystalline
rocks and in a few sinks. Cs also has a much greater resistance time. A better
understanding of the comparative behaviour of the elements can thus be gained
by considering the relative reactivity of the eiements on the basis of the average
time which they spend in seawater before removal to the sediments.
Trace elernents in seawater have two major extemal sources:
1) the atmosphenc or riverine transport to the sea of weathering products of
continental rocks, and
2) the introduction of material by interadion of seawater with newly formed
oceanic cnist basal at ridgeeest spreading centres via both high
temperature hydmthermal activity and low temperature interadion with
newly fomed crust (Worig et al., t 983; Kennish, 1994).
Table 3.1 Mean oceanic conœnttaüons and residence times of the elements of interest
MAJûR ELEMEMS
Na
Mg S
Ca
CONSERüATM M E T U Mo
3.3.2 Metals with Consewative Behaviour
Al Mn Co Fe Pb
Among the elements of interest in this work, lithium (Li), cesium (Cs), and
Ppm
10.8 x ld 1 . 2 8 ~ 10'
~ 7 x l û )
4.15 x id PPb 11
rubidium (Rb), like their more abundant cwnterparts sodium (Na) and potassium
Yn 8.3 x 107
1.3 x107
1.1 x l d
Yrr
8 2 x l d
' Main source : Broecker and Peng, 1982 Main sources : Bmecker and Peng, 1982: Riley and Chester, 1983; Kennish. 1994
1
1 xlQ'
2 x IO-' 4 x 1 6 t xlQ'
(K), are considered as conservative (Duxbury, 1989; Millero and Sohn, 1992).
6.2 x 1 d
1.3 x ld 3 .4x ld
5.4 x IO' ld (in the dee~ Mar coiumn)
The conœntration of the metals that belong to this category changes primariiy as
a consequene of the m m of water bodies wtiich have obtained dierent
concentratiocis in bouridary reg-, or the addition or removal of water by
precipitation and evaporation at the ocean surface. This charaderistic shows that
their geochemical reacüvity is low, therefore their mean oceanic residence time is
in the order of lo5 years (Riley and Skinow, 1975; Kennish, 1994). Also, the
concentrations of the 'conservative" metals show a strong relationship with
salinity values. These metals behave like the major elements in seawater
although they do not reach high concentration levels because they are less
copious in source materials, such as erustal rocks (Fumess and Rainbow, 1990).
The consenfative behaviour of the trace alkaii metals Li, Rb, and Cs c m
be defined only within the limits imposecl by the precision and accuracy of
analytical methods. In case of Cs, for instance, there is a greater variation in
reported concentrations than for Li and Rb (Riley and Chester, 1983). This may
reflect poorer precision and accuracy because of the lower concentrations: Cs,
2.2nmoükg or 0.29ppb; Li, 25pmoVkg or 175ppb; Rb, 1 -4pmoIkg or llgppb, at
35 'la salinity (Wang et al., 1983; Fwness and Rainbow, 1990). Although al1
elements undergo some recyding within the seawater column, including the
wnservative elements, the recyding flux of consenfative elements is low relative
to their concentrations in seawater (Goldberg, 1975; Kennish, 1994).
Molybdenum (Mo) behaves conservatively (Figure 3.1) and forms
oxyanions (MOOZ) in seawater. Fumesa and Rainbhv (1990) have reported that
Mo concentrations in seawater (North Atlantic Ocean values) can be as low as
90 -135 nmoükg or 8.6 -12.9ppb. Collier (1 985) and Mjllero (1996) report that Mo
concentrations in the Pacific Ocean average 110 m U k g or 10.5p@2
(Figure 3.1). In the Mediterranean Sea, the Mo average semater coricentrabim
is 1 1 ppb (Emelyanov and Shimcus, 1986; Saager et al., 1993). This metal foms
stable oxy-anions in aqueous solutions and tends to have Iow geochemical
reactivity. The mean oceanic residenœ time for molybdenum is estimated to be 7
X 1 O' (Wong et ai., 1983; Kennish, 1994).
Figure 3.1: Profile of molybdenum (Mo) in seawater, showing its wnservative behaviour (Millero and Sohn, 1992).
Uranium (U) is considered to be wnservative, as well (Table 3.1). The
uranyl ion fonns carbonate complexes and appears to have a stable
concentration in the oceans, averaging 13.5 nmolkg w 3.2ppb at 35 Oi, salinity
levels (Chen et al., 1986; Furness and Rainbw, 199û).
3.3.3 Metals with nutrient - like behaviour
The trace metals examined in this study that fall into this category are:
cadmium (Cd), nickel (Ni), zinc (Zn), copper (Cu), vanadium 0, barium (Ba) and
ehromium (Cr). These elements show a degree of positive correlation with
micronutrients, nitrate, phosphate and dissolved silica (Riley and
Chester, 1983). As a result, the above mentioned metals are charactefised by
notable depletion in surface waters and a rapid increase in concentr&on in
deeper seawater layers (Broedeer and Peng, 1982; Libes, 1992). Furthemore,
these elements are involved with the flux of particulate material of biological
origin. This flux, driven by primary productivity, is transrnitted from the euphotic
zone to deeper waters, where subsequent release to solution occurs dunng the
microbial decomposition of organic material or the dissolution of mineral phases
originally produced as skeletal material by organisms in the upper ocean, such
as biogenous silica (opal) and calcium carbonate (Libes, 1992). The rnetals that
follow this flux serve specific metabolic requirements or are assaciated with the
organic material. They have intermediate mean oceanic residence times and
have been referred to as recyclecf rnetals, bio-limiting (for strongly surface-
depleted elements) and biwntemrediate (for detectably but less strongly surface-
depleted elements) (Wang et al., 1983; Furness and Rainbow, 1990; Millero and
Sohn, 1992).
Cadmium (Cd) is an element with no knawn biological function but with a
pronounced bond with biogenous particulate material. The behaviour of this
rnetal c m serve as an example to illustrate the most important charaderistics
that result from this bond. For instance, North Atlantic Cd distributions (Figure
3.2) show that surface concentrations are below 0.05 nrnoUkg or O.OO5ppb (Boyle
et al., 1976, Millero, 1996). In the lower main thennodine region, however, a
rapid increase in concentration ocarrs to a maximum, followed by a sligM
decrease to relativeiy cor#tant values of 0.35 nmokg or 0.04ppb in deeper
seawater layen (Wmg et al., 1983; Millero, 1996). This profile charaderizes
nutrients (Figure 3.3) and indicates the similar behaviour of Cd with the
constituents (Le. phosphate) that are cyded in the formation and decomposition
of soft organic tissues (Boyle et al., 1976; Furness and Rainbow, 1990; Millero,
1 996).
Figures 3.2 and 3.3: Profiles of cadmium (Cd) and phosphate (POd) in North Atlantic and North Pacific oceanic waters. The Cd behaviour in seawater resembles the nutnent-type profile of PO4 (by Libes, 1992).
Zinc (Zn) also belongs in the Recyded metals gfoup. This metal is highly
depleted in open ocean surface waters. It inueases in concentration in the main
themiocline region and it appears to have a close relationship with dissolved
silicon. This relationship implies th& the main carrier phase to downalumn
transport is likely to be the skefetal material. ln North Atlantic surface waters, Zn
concentration is around 0.05 nmoUkg or 0.003ppb. At lOOOm depth Zn levels
increase to 1.7nmollkg or 0.02ppb. In the Meditenanean seawater, Zn values are
2.7nmoVkg or 0.1 7ppb at 1-1 00 m depth and inaease to 4.7 nmoUkg or 0.3ppb at
1 Sû-2i'ûûm depth (Tankere and Statham, 4996)-
Nickel (Ni) shows also a nutrient-like behaviour but with much less
marked surface depletions than cadmium and zinc (Sciater et al., 1976; Fumess
and Rainbow, 1990). Concentrations in open North Atlantic surface waters are
about 2 nmolkg or 0.1 Ippb, whereas in deep North Atlantic waters the Ni levels
are around 6 nmolkg or 0.3ppb (Yeats and Campbell, 1983). In Mediterranean
seawater, Ni concentrations range from 2.4 nmolkg or 0.13 ppb at 1-100m depth
to 3.1 nmolkg or 0.17ppb at 150-2700m depth (Tankere and Statham, 1996).
Copper (Cu) is a recyded metal that is also characterized by surface
depleted concentrations, relative to those in deeper waters. For the North Atlantic
Oman, the upper water column of concentrations are reported to be 1.1 to 1.7
nmollkg or 0.07ppb to 0.lppb with increases to about 2 to 4 nmolkg or 0.12ppb
to 0.25 ppb in deep waters (Yeats et al., 1983; Kennish, 1994). In the
Mediterranean Sea the Cu levels range from 3.5 nmollkg or 0.2 ppb (surface
waters) to 9 nmoükg or 0.6 ppb in deeper water bodies (Laumond et al., 1984;
Boyle et al., 1985).
lnstead of following a nutrient-element type distn'butÏon, Cu is substantially
influenced by in-situ deep water scavenging at a constant rate of 830 years.
Thus, the unique distribution of Cu can be explained by rapid scavenging in
surface waters, continued scavenging in intermediate and deep waters and an
upward flux from sediments wused by early diagenesis whereupon the Cu is
recycied back into the overiying water column (Riley and Chester, 1983: Fumess
and Rainbmv, t99û)
Vanadium (V) is predicted to m r in the +5 oxidation state, primarily as
HVOI '-, HzVOÜ and NaWOi (Fumess and Rainbow, 1990; Kenniai, 1994).
Wmg et al. (1983) have reportad that vanadium concentrations in Eastern North
Atlantic averaged 23 nrnoükg or 1.1 7ppb and revealed no depth-related patterns.
Collier (1984) and Middelburg et al. (1988) have also reported that vanadium
concentrations in North Pacific and North Atlantic, respectively, show small
variations with location and depth and have no indication of a pronounced
surface depletion. In the Mediterranean Sea, the vanadium average seawatet
concentration is 31 nrnolkg or 1.58ppb (Emelyanov and Shimcus, 1986;
Gabrielides, 19%).
Because of its occurrence as an oxy-anion (Le- IWO4 2-1 HIVOi and
NaHV04') in seawater, vanadium is normally compared to molybdenum.
Molybdenum also forrns oxyanions in seawater and behaves consewatively.
Both elements show small variations witb depth in their concentrations.
Hawever, a significant d i i n œ between the chernical characteristics of the two
metals is the rnean oceanic residenœ tirne. For vanadium, this value is 4.5 x 1 o4
years, an order of magnitude lwer than mat fw molybdenum, which is 8.2 x 10'
years (Middelburg et al., 1988; Kennish, 1994).
6arium (Ba) has been related by several auaiors to the Recyded Metals
group ( B m n et al., 1982; Kennish, 1994; Millero, 1996). Ba geochernistry
resembles that of the nutrients in an oceanic environment (Figure 3.4 and
Figure 3.5). Like silica, Ba enters into deep cycle of generation and dissolution,
charadefistic of skeletal components and other slowiy dissolving mineral phases
(Furness and Rainbow, 1990). Bowen et al. (1982) have reporteci that Ba
concentrations in the Indian-Antardic Ocean, noRh of the Antarctic Convergence,
increased from 54 nmoükg or 7.3 ppb at the surface to 105 nmolikg or 14.3 ppb
below 3Skm depth. In the Atlantic Ocean (Figure 3.4), Ba concentrations exhibit
a surface depletion (40 nmolikg or 5.4ppb) that is followed by an increase in
deep waters, higher than 80 nmolikg or 10.9 ppb (Millero, 1996). In the
Mediterranean Sea, dissolved Ba in seawater ranges between 45 nmolkg or 6
ppb at the surface and 210 nmoUkg or 30 ppb in deep waters (Emelyanov and
Shimcus, 1 986; Hem et al., 1999).
Figures 3.4 and 3.5: Profiles of barium (Ba) and silica (Si) in Atlantic oceanic waters. Ba, Iike silica, shows a surface depletion and regenerates in deep seawater reaching maximum levels (Millero, 1 996).
Chromium (Cr) appears to have a nutrient-type distribution. Previous
research has shown that total dissolved Cr contents in the north-west Atlantic
Ocean were depreted in the surkœ water (335.2 nmoUkg or 0.17-0.27ppb) but
reached a coristant level (4.2 m ü k g or 0.21 ppb) at greater depths (Wong et
al., 1983; Millero, 1996). In the Mediterranean Sea, Cr concentration is 65
nrnolkg or 3.4 ppb in surface waters and increases up to 78 nmoükg or 4-1 ppb
in deeper water bodies, at 220-2500m depth (Emelyanov and Shimcus, 1986;
Furness and Rainbow, 1990).
3.3.4 Scavenged Metals
The third major category includes elements that have a nonconservative-
type behaviour. Their oceanic residence times are short (>do3), which means that
there is efficient removal of these metals by oxidative or hydrolytic scavenging on
partides (Fumess and Rainbow, 1990). Their concentrations are reduced
significantly with distance from sources. These sources can be at the boundanes
of the ocean with the atmosphere, the seabed, the continental lithosphere or
within the ocean itself. Scavenged rnetals are considered to be useful tracers of
mixing and transport in the oceans (Riley and Chester, 1983). In this study, the
metals that fall in this group are aluminum (Al), rnanganese (Mn), cobalt (Co),
irm (Fe) and lead (Pb).
Aluminum (Al) is a highly hydrolyzed and highly particfe-ceactive metal
that has the most important characteristics among the scavenged metals group.
A profile of this metal in the North Atlantic (Figure 3.6) shows systematic trends
with depth, with a decrease in concentration from surface values of about 35
nmolkg or 0.9 ppb to about 20 nmokg or 054 ppb at 1 km depth, followed by an
increase to about 35 nmoükg œ 0.9 ppb bekw 3.5 km (Libes, 1992). The
decrease in surfaoe vaiues is caused by adsorption or uptake by plant material
M i l e the increase in coricer~tr~on in bottom waters is due to resuspension of AI
from the sediments (Wor~g et al., 1983; Libes, 1992; Millero, 1996).
Mediterranean Sea Al concentrations range from 30 nmokg or 0.7 ppb in the
surface waters to to 60 nmollkg or 2 ppb in deeper water layers (Emelyanov and
Shimcus, 1986; Millero and Sohn, 1992).
Figure 3.6 Profile of aluminurn (Al) in oceanic waters. The Atlantic profile clearly shows a scavenging behaviour in surface waters followed by an increase in bottom waters (Millero and Sohn, 1 992).
Manganese (Mn) has high partide reactivity and consequently short
mean oceanic residence times, of 1000 years (Riley and Chester, 1983; Furness
and Rainbow, 1990; Kennish, 1994). Mn undergoes a change in oxidation state
between oxidizing and reducing environments and there is a marked difierence
between these oxidation states in tens of geochemical mobility (Fumess and
Rainbow, 1990). The oxidation of Mn (+2) to Mn (+4) is mediated mainly ai
partide surfaces and between the two oxidation states, Mn (+2) is the
themiodynamically stable oxidation state and the element is then more soluble
(Furness and Rainbow, 1990; Kennish, 1 994).
The general features in the distribution of Mn are similar to those in Figure
3.7. Enhanced Mn levels in surface waters, with concentrations around 1 to 3
nmoüikg or 0.05 to 1.5 ppb (North Atlantic surface water), reflect the advection of
manganese h m sources such as rivers at the ocean margin in certain areas, but
eolian inputs are also important (Bowen et al., 1982; Millero, 1996). Oceanic
deep waters appear to have lower Mn concentrations, ranging from 0-6 nmoUkg
or 0.033 ppb (Northwestem Atlantic) to 0.25 nmollkg or 0.01 ppb (Northeastem
Atlantic Ocan) (Furnes and Rain bow, 1 990; Miliero, 1996). In Mediterranean
Sea, Mn concentrations are strongly elevated in surface waters, between 2
nmokg or O. 1 1 ppb and 3.4 nmokg or 0.1 9 ppb), and decrease exponentially
with depth to very low values, between 0.06 nmoükg or 0.003 ppb and 0.4
nmoUkg or 0.02 ppb at 1000 - 2000 m depth (Saager et al., 1993).
Figure 3.7: Ptofile of manganese (Mn) 1 i" -nr *ers (No* Atlantic]. m enhanced surface oorrcentrati~~\~ are fdlowsd by a decrease in deeper waters, due to mvenging pmœsses (Libes, 1992).
ODD
Cobalt (Co) is a metal aiat accuris at very low levels in seawater. Although
it is of oceanographical interest through its accumulation in manganese nodules,
tiffle is known of its oceanic distributiori. Co exists in seawater at concentrations
below 0.1 nmoükg or 0.005 ppb (Danielsson, 1980; Millero, 1996). Certain
features of this metal indicate a similarity with Mn oceanic profile, with enhanced
concentrations at the surface and a decrease with depth. North Atlantic surface
Co concentrations are reported to be around 0.08 nmolkg or 0.004 ppb Mi le
deep water levels are betow O.Q5 nmoUkg or 0.003 ppb, at 1000m depth
(Kennish, 1994). In the Mediterranean Sea, surface concentrations range from
16 nmolkg or 1 ppb at O - 50m, to 32 - 50 nrnolkg or 1.9 -3 ppb at 1000 -2000m
depth (Migon and Nicolas, 1998).
Low cobalt concentrations may indicate that this element is rapidly
removed from seawater, probably in association with manganese oxide phases
(Furness et Rainbow, 1990). Furthemore, low concentrations of Co may imply a
possible contribution of this metal as a biolimiting element in seawater.
lron (Fe) behaves similarly to manganese in seawater, as bath elements
undergo oxidation. In oxygenated seawater, Fe (+2) oxidizes to Fe (+3), which is
strongly hydrolyzed in the marine environment, fonning various (oxy)hydroxide
phases of very low solubility (Miltero, 19S; Croot and Hunter, 2000).
The biological utilization of Fe is critically dependent on the readivity of
the elernental f m s in Seawater- Fumess and Rainbow (1990) and Croot and
Hunter (2000) have repated that Fe is a signifiant Iimiting nutrient for
phytopianiâm growth in openasan, nutrientnch waters. The biomass
production in coastal waters is aiso Meded by the Fe input, either from
terrestrial sources (Le. rivers) or from resuspension of bottom sedirnents (Croot
and Hunter, 2000). Martin and Fitmater (1988) and Martin et al. (1994) have
shown that the addition of Fe in amounts in the order of nmokg (i.e. 1 ppb) in
nutrient-rich Pacific Ocean waters leads to increased utilization of nitrate.
According to these researchers, this suggests that the availability of iron rnay
Iimit the gmwth of phytoplankton in seawater.
Landing and Bruland (1987) reported surface concentrations of dissolved
iron in the Pacific Ocean as high as 0.75 nmollkg or 0.042 ppb to 1.25 nrnolkg or
0.07 ppb that decreased offshore to about 0.5 nmoükg or 0.03 ppb. Oecreased
concentrations occur in deeper water layers, but the levels of diçsolved Fe
increase at depths wtiere oxygen minima occur (Landing and Eniland, 1987). In
Mediterranean seawater, Fe concentrations range from 1 - 6 nrnolîkg or 0 . 0 s
0.336 ppb (Saager et al., 1993). It should be noted that accurate rneasurement of
iron is particularly diiailt due to aie low levels of this element in seawater, and
the predominance of the element as a contaminant in sampling analysis (Fumess
and Rainbow, 1990; Millero, 1996).
Lead (Pb) occurs in North Atlantic open ocean waters at concentrations
h m 0.005 ta 0.175 nmoükg or 0.001 b 0.036 ppb, and its oceanic distribution is
significantiy influenced by anthropogenic activities (Fumess and Rainbaw, 1990).
Schaule and Patterson (1981) detefmined Pb concentrations in the North Pacific
oceanic surface water to be 0-025 b 0-075 mUkg or 0.01 to 0.01 5 ppb, wiîh the
concentrations increasing frwn ttie eoast to the open ocean waters- Oeeper
water values in the sarne area, at depths below 3500 m, were reported by these
authors to be close to 0.005 nmoükg or 0.001 ppb (Furness and Rainbow, 1990;
Millero, 19%).
In the Mediterranean Sea, Pb concentrations range from 0.05 ppb
(surface waters) to 0.044 ppb in deeper water bodies (Laumond et al., 1984,
Migon and Nicolas, 1998).
The enhanced concentrations of lead in the upper part of the water
column relative to deeper water layers, is due to the short residence tirne of this
element within the water column (approximately 100 years in the deep-water
colurnn) and to its anthropogenic atmospheric input (Wong et al., 1983; Rivaro et
al., 1998).
PART 2
3.4 Seawater Analysis
Analysis of trace metals in seawater appears to be one of the most
appealing subjeds for research in analyücal chemistry (Bloxharn et al., 1993; GiII,
1997). The extremely low detedon limits coupled with the chernical interferences
ftom the seawater rnatrix are viewed as a challenge and, therefore, several
methods have been developed for the determination of trace metals in this
medium (Jarvis et al., f 992; Bloxham et al-, 1993; Field et al-, 1999).
In order to eliminate the problems assodatecl with the camplex nature of
semater, most of these methods indude a plethora of separation -
preconcentration procedures such as solvent extraction and ion exchange
(Miyawlci and Reirner, 1993; Orians and Boyle, 1993; Batterham et al., 1997),
hydride generation (Santosa et al., 1997) or on-line preconcentration (Mclaren et
al., 1993). These rnethods are usually timeansuming, involve high levels of
contamination and have interference problems (Rodushkin and Ruth, 1997; Field
et ai., 1999). Altemate rnethods facus on diirent sample introduction strategies
for lnductively Coupled Plasma Mass Specîrometry (ICP-MS), such as
e l m e r m a l vaporisation (ETV). However, oiese rnethods are also slow and
cannot be used for multi-elernent detemination (Chapple and Byme, 1996).
The direct deteninatim of tracs met& in seawater can significantly
reduœ the time of analysis, laboratory preparations and contamination nsk
associated with traditional preconcentration techniques- The application of
double-focusing, high-resolution indudively coupled plasma mass-spectrornetry
(HR-ICP-MS) in seawater analysis m r s the opportunity for developing
techniques that allw direct detemination of trace elements in seawater
sampîes. These rnethods would require no sample pretreatrnent 0th- than
acidiition, dilution and intemal standardisation. As well, by using double-
focusing HR-ICP-MS, the spectral interbcences can be eliminated, the sensib'vity
of the method increases notably and the technique can be used for muM-element
anaiysis
Analytical techniques fix seawater analysis nmally involve combining
sample preconcentration methods with ICP-MS- McLaren et al. (1993) presented
a method for trace metals analysis in seawater by Q-ICP-MS, which inciuded an
on-line preconcentration of trace metals from saline solutions. A chelation
concentration system was operated both with colurnns provided by the
manufadurer and with colurnns containing silica-immobiiii 8-hydroxyquinoline
that allowed the simultaneous detemination of Fe, Mn, Co, Ni, Cu, Zn, Cd, and
Pb. Detedion limits for the anal* mnggd h m 0.3 ppt for Cd to 55 ppt for Ni.
The method was validated by the analysis of coastal and open ocean seawater
œrtified referenœ materials (CAS2 and NASS-3 respedively). The drawbadcs
of this method were:
High blank values that degraded the quality of the Co analysis
Spedrascopic interferences that caused difficuiües in the determination of Fe
Time of the analysis (1 0 minutes)
Beaudiemin (1995) appl i i an on-iine standard addition method with ICP-
MS using Flow injection for dired determination of Mo in seawater (NASS4).
The method required injedion of the sarnpie into twm diirent carriers (Le., a
biank and a standard with a greafer concentration than that of the sample) as
well as injecüm of the standard in the Mank canier. The method accounted lor
the change in sensiüvity induced by the sample upon its injection into the
standard carrier. in the best conditions, orie replikate mulü-elemental analysis by
the on-line standard a d d i methad was acamplished in 200s (using 100-pL
-hjedkm)- A b . the set up prwided semitMy similar to that expeded from
di- continm n e b u l i i n of the sarnpie- The results had excellent
agreement with the certified values- The major dtawbadt of this method was:
A degradation in precision mpared to peak height calibration, which results
from error propagation of the greater number of parameters being detmined
to find concentration.
Batterham et al. (1997) combined an off-line solvent extraction procedure
with Q-ICP-MS for the detemination of Cd, Co, Cu, Fe, Ni, Pb and Zn in
seawater. The solvent extraction procedure used an organic solvent
(dithiocarbamatediisobutyl ketone). Externa[ standards were used for ICP-MS
calibration. The method gave a 5% reproducibility except for Fe (7%) and low
detecüon limits: Cd 0.2 ppt, Co 0.3 ppt, Cu 3 ppt, Fe 21 ppt, Ni 2 ppt, Pb 0.5 ppt
and Zn 2ppt The limitations of this method were:
Long laboratory pretreatment,
Risk of contamination during the prewncentration steps,
lsobaric interferences, that hindered the accurate determination of Fe
Rodushkin and Ruth (1997) developed a direct method for the
detemination of 15 trace metals (Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb,
U, V and Zn) in seawater samples by HR-ICP-MS. The samples were acidied
and diluted, but no other pre-treatrnent step was taken. The authors of this study
combined intemal standaramon with non-matrix matched extemal calibration
cunres. Sets of elements were chosen as intemal standards for the analytes. The
method was validated by the analysis of three certified reference materials
diluted 2-5 fold in purified 0.14 M HNOJ . The reference materials that were used
in this technique included open acean watw (NASSa), coastal water (CASS-2)
and estuarine water (SLEW-2). This method demonstrated rapid, accurate frutti-
element detemination of trace metals at pg ml" fevel directly in seawatter.
However, there were certain limitations:
Unresolved Mo0 interferences (for Cd) and insuffident intemal standard
correction (for Zn) degraded the quality of the analysis for these two
elements,
Blanks for a number of elements were comparable to analyte concentrations
in the diluted seawater,
The intemal standardization was complicated.
Field et al. (1999) introduced a new method for the direct detemination of
10 trace metals (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) in coastal seawater,
using desolvating micronebuIization HR-ICP-MS. The samples were acidiied
with nitric acid and diluted but only a small amount of seawater sample was used
(50 PL). Analyses were standardized by a matrix-matched extemal calibration
cuve with variations in sensitivity conecfed by nomalising to the natutal intemal
standard Sr, a consetvative ion in seawater. In mis work, the measured values
for most elements agreed with certified values (CASS-3), within 95% confidence
Iimit and a precision of 3-12 % for al1 elemerits exeept for Cr. Using an MCN-
6000 desolvating system reduced molybdenum oxide interferences. This allowed
better detemination of Cd relative to previously published studies (Rodushkin
and Ruth, 1997). However, the results for Cr, Cd and Zn were less satisfactory.
3.5 Summary
The above mentioned analytiçal techniques indicate that rnethods that
combine preliminary math separation with indudively coupled plasma mas
spectrometry have limitations with respect to the time of the analysis, the
contamination danger due to extensive faboratory sarnple preparation, the
spectral interferences and the cost of the satup. As well, these rnethods cannot
be used fw multi4ernent analysis and are not suitable for the determination of
monoisotopic elements, such as Co.
Direct seawater analysis by double-focusing HR-ICP-MS appears to be
fast, accurate, with low contamination risk, good reproducibility and significantly
less spedral interference probms. As weil, double-focushg HR-ICP-MS has
greater sensitivity than conventionat ICP-MS and lower detection limits.
Rodushkin and Ruth (1997) and F'reld et al. (1999) demoristrated that their
rnethods can be used for rnulti-element simultaneous analysis.
HOWBW, elements such as Fe, Co, Cr, Cd and Ln are difficult to analyse
accuately in a seawater matrix, even with double-focusing HR-ICP-MS
techniques. Far example, Cr, Cd and Zn determinations need further
investigation and improvement.
3.6 Seawater Anawi in thîs ln- . .
This thesis &mmûaWs a dired Sgawater anafysis for 17 trace metals
and four major dements by using doubie -q HR-ICP-MS (fumer discussed
52
in Section 4.3). This method incorporates the instnirnentation used &y
Rodushkin and Ruth (i997) as well as Wir procedure for auntetactihg memry
effects ( M o n 4.5). The quantitative calibrabian and the internat standardizatian
methad, however, in this invesfigation is differP!nt. MatrDr-adjusted extemal
calibration was ernployed as a calibration procedure and one elentent, indium
(In), was used as the intemal standard for al1 analytes. Laboratory produres
were further improved as indicated by the lower detedion limits and blank values
oMained in this research (Table 4.2). The foilowing Chapter will elaborate on the
method of anaiysis.
CHAPTER 4
Method of Analysis
4.1 General
This Chapter describes in detail the method used in order to determine the
concentrations of major elements and trace metals in seawater sampies frorn the
Great Australian Bight. The seawater samples were analyzed using a Çinnigan-
MAT Element 1, double-focusing HR-ICP-MS. A detailed desa'iption of this
highly sophisticated equipment is also inciuded in this chapter.
Issues related to the analysis of the trace element and the major element
contents in the seawater matrix by double-focusing ICP-MS are also examined in
depth induding interferences, appropriate calibration, analytical strategies and
data interpretation techniques.
4.2 Instrumentation
4.2.1 Introduction
Among the different methods for the determination of trace and ultratrace
elernents and isotopic composition in inorganic materials, ICP-MS is well-
established as a universal, powerful and very sensitive muiti-element mthod
applicable in many fields of modem science and technology. The first analytical
mass spectfa from an ICP were obtained by RS. Houk in 1978. Sciex. inc.
introduced the first commercial instrument for ICP-MS at the 1983 Pittsburgh
Conferenœ (Houk, 1986). This type of instrument attracted the researchers in
geology prirnarily because it combines low instrumental detection limits with a
great sensitivity and a capability for rapid and accurate multielement analysis.
4.2.2 Choice of an ICP system
The indudively coupled plasma is used in atomic emission and absorption
spectroscopy (AES and AAS) as well as in mass spsctrometry for trace elements
analysis (Boss and Fredeen, 1989; Scoag and Leary, 1992). ICP-MS has the
advantages of part-per-trillion detection Iimits. It is able to detect al1 elements with
detection limits often 1-2 orders of magnitude better than for ICP-AES
(Thornpson and Walsh, 1988; Stentzenbach et al., 1994; Becker and Dietze,
1997). The ICP-MS method exhibits better sensitivity in seawater analysis than
ICP-AES, although the sampling orifice may Iimit the working detedon lirnits in
both because of high levels of dissolveci xilids.
The Iow detection limits of the method in combination with the capability of
scanning for several elements at the same time makes ICP-MS a much preferted
analytical tool in marine analyücal chemistry than the ICP-AES option. ICP-MS
sufFers the same physical interferences as ICP-AES because sample introduction
limitations are similar, However, in ICP-MS the spednim is rather dearer and
simpler aian the ICP mission spednim (lbmpson and Walsh, 1988; Bradshaw
et al-, 1989; Hall et al.. 1 s ) .
Two types of ICP-mass spedrometers are commonly in use: Quadropole
mass spectrometers (Q-ICP-MS) and double-fmsing ICP-MS with highniass
resolution (HR-ICP-MS) (Section 4.23.1). It is mentioned that mass resolution R
is generally defined as WAm, in which hm is the mass difference to achieve a
valley of 10% between two neighbufing peaks of identical intensity at a mass rn
and a mass m+Am. The doublefocusing mass spectrometers combine a
magnetic and an electnc sedor field analyser. Quadropole mass spectrometers
offer an insufficient resolution for the separatim of chemimlly diierent ions at the
same nominal mlz value (Janris et al., 1992). In a double-focusing mas
spectrometer, the ion bearn is fowsed efficiently, the ion count rates are
comparable to or higher than those obtained with quadrupoles. As a result,
detection Iimits can be better with the double-focusing instrument and the
analytical limitations ftom spedroscopic interferences are reduced (Thompson
and Walsh, 1988; Jarvis et al., 1992; Field et al., 1999). The choice of ttie
Element magnetic sector HR-ICP-MS for the analytical part of this study was
based on the above-mentioned advantages that this technique features in
wmparison with other analytical methds of cornplex matrices.
4.2.3 Genenl Description of the ICP-MS Instrument
Typically, an ICP-MS combines twa useful analytical tmls. The first
component is the InductiveIy Coupied Plasma The plasma serves as an
excellent source of ions for a mass spectrometer. which is the second
component The Mass S9ectr#neter Deteam separates ions by their masses
and subsequentiy detects them ( F i 4.1). The process of the ICP-MS is
desaibed below. By definition, a plasma is a collection of charged partides
resembling a gas but differing fiom it as it conduds electncity and is affecteci by a
magnetic field (Thompson and Walsh, 1988). One of the most efficient methods
of generating a plasma c m be achieved by inductively coupling a gas to a Tesla
mil (Jarvis et al., 1992). Inductively Coupled Plasma functions by allowing a flow
of gas (argon) through a quartz torch. The basic construction of the quartz
plasma tordi consists of three concentric tubes that are encapsulated by a
copper load mil. The load coi1 is çonnected to a radiofrequency genefator of
either 27 or 40 MHz A power source provides 700-1500 W when directed
through the mil. This induces an oscillating magnetic field (indudively coupied)
at the top of the torch (Thompson and Walsh, 1988; Jarvis et al., 1992)- To
initiate electrical conductivity in the gas as it flows through the mil, a Tesla spark
is used and inductive heating of the flowing gas then maintains the plasma
buming at temperatures of 6000-10000 K (Pupyshev et al., 1999).
The free electrons created by this process are aceelerated by the
rnagnetic field generated and bombard other gas atorns, which, in tum, cause
further ionization and aius produce the plasma Wame". Sample introduction is by
means of a amer argon gas flow through the central tube in the quartz torch.
Liquid samples are nebulised into an aerosol before k ing carried into the
plasma torch. This function is perfonned by the nebuliser and spray chamber, in
order to separate large and small droplets. Once a sarnple reaches the plasma,
vaporization, atomization and ionization of the analyte occur almost
simultaneously (Jawis et al., 1992). Ions generated from the plasma are sampled
by means of a sampler and skirnrner cone. The ions of the sample pass through
the aperture of the cones into low-pressure chambers. Ion lenses (which are a
series of eledrodes) are used to Yocus" the ion bearn, before reaching the mass
analyser where ions of only one rnass-to-charge ratio at a time are foeused on
the exit slit (Thompson and Walsh, 1988; Stewart and Olesik, 1998).
An electron multiplier detector is used to ampli@ the electron pulse
created from each ion impact The ICP-MS measures a charaderistic intensity
(countsis8cond) for a given concentration of an element.
4.2.3.1 Double-Focusing ICPMS in th@ Study
The Double-Focusing ICP-MS instrument used in this study was the
ELEMENT I (Finnigan-MAT, Bremen, Gemany). The FinniganWT Element I is
a double focusing sector field instrument with reverse Nier-Johnson geometry. A
double-fbcusing Secfor field mass spectmmeter combines a 600 magnetic sedor
f&d for direction focusing and a 900 elednc sedor field for energy focushg of ion
beams (Moens and Jakubowski, 1998). 60th magnetic and electrk sectof
instruments have angular focusing praperties and the combined system foarses
by angle and energy. This is where the term 'double focusing" originates
(Becker and Dietze, 1997; Moens and Jakubawski, 1998)-
Reverse geometry is used because the elednc sector is placed after the
magnetic sedar, whereas traditionally, the eiectric analyser is before the
magnetic sector field (Moens and Jakubowski, 1998). This is wnsidered an
advantage because the high ion currents h m the source are first reduced by
mass analysis and only ions of the selected mass are subjected to the
subsequent energy analysis. This arrangement Ieads to an improved abundance
sensitivity as weli as to the reducüon of thé noise (Becker and Dietze, 1997).
The most important capabili of double focusing instruments is high mass
resolution. High mass resolution can separate spedroscopic interferences from
the afFected analyte isotope (Skoog and Leary, 1992; Mclaren et al., 1993). The
reduction of spectroscopie interferences can greatly improve the quality of the
analysis, as is discussed in the follawing sedibns (Section 4.4.1). lncreasing
resolution, however, results in decreased peak width. The interfering molecule
cm be separated fiom the analytical isotope, but not without a redudion in
sensitivity (Jain et al., 1998; Moens and Jakubowslzi, 1998). The Finnigan-MAT
Element I can be operated in low resolution mode (LRM, mlAm = 3W), medium
resdution mode (MW, M m = 3000) and high resolution mode (HRM, mlAm =
7500). The sensitMty decreases by a factor of approximately 13 when going from
LRM to M M and by a factor of 11 from MRM to HRM (Rodushkin and Ruth,
1997).
4.3 Mettiodology
A doublefocusing ICP-MS (as desxibed in Section 3.2.2 ) was used for
the detmination of the concentrations for 17 trace metals ( Mo, Pb, U, V, Cr,
Mn, Fe, Co, Ni, Cd, AI, Cs, Ba, Cu, Zn, Rb and Li ) and 4 major elements ( Na,
Mg, S, Ca ) in samples that were collected in the Great Australian BigM marine
environment. In total, 63 samples were analyzed. These seawater samples were
coliected by Dr. T.K Kyser from 27 stations at various depths mainly surface
(0-200m depth) and intermediate (20e1000m depth) waters-, dufing the RV
Franklin voyage (FR 03/98) along the eastern part of the Great Australian Bight,
in March 1998. Samples were calledecl in acid leactied Niskin bottles, filtered
(using a 0.45pm filter) and acidified with ultrapure HNOa Utmost care was taken
on ship to minimize sample contamination.
For the analysis of the trace elements, the samples were diluted 10-fold
gravimetrically, without matrix separation. Instead, befare the GAB seawater
samples were introduced into the ICP-MS, maûix-adjusted extemal calibration
was employed as a calibration procedure in order to counteract possible matrix
&eds that are a wmmon problem in seawater analysis. The determination of
the major elements (Na, Mg, S, Ca), however, did not involve interference
effects from the seawater matrk Consequently, after a 50,000-fold dilution of
the seawater samples, simple Iinear calibration airves were created for each
elernent M a j p elements were a n a m in medium tasduüon (MR). ngum 4.2
describes the steps takm mng the BnaIyhl for îhe trace metals
and the major elements detemiinatiori, from the sample dilutions Stage to the
introduction to the double-focusing ICP-MS and, eventually, to the data
collection.
Samole Dilutions
Trace E l w n t s
Blank Preparation
Data Colledion - Statistical Anaiysis y F ~ 4 . 2 Descn'pb-onof the proeedrre fobmâ for the analysis of the trace metals and the major elements
The methods ernployed were validated by analysis of open ocean
seawater (NASS-5 or North Atlantic Surface Seawater), wastal seawater
(CASS-3 or Coastal Atlantic Surface Seawater) and estuarine (SLEW-2 or St
Lawrence Estuarine water) seawater standards. NASS-5, CASS-3 and SLEW-2
were analysed after a IO-fold dilution. These Certified Referenœ Materials
(CRMs) were obtained from ttte National Research Council of Canada. Validation
of the major elements (Na, Mg, Ca, S) was dom with a certifieci reference
material from High Purity Standards (SWHPS) hich was diluted and analyzed
as the other Reference Materials used in this method.
For the dilution of al1 standards, blanks and Certified Reference Materials
(CRMs), as well as the samples, 2% HN03 acid with 10 ppb In as Interna1
Standard was used (furtfier diswssed in Sedon 4.4.2.1). AI[ the above-
mentioned dilutions were prepared in a clean laboratory.
The HR-ICP-MS was operated in low resolution for Mo, U, Cs, Ba, Al, Pb
and medium resolution for VI Cr, Mn, Fe, Co, Ni, Zn, Cu, Cd, Li, Rb. DifMent
levels of resolution were prefened because of the presence of isobaric ovedaps
with masses very similar to the analyte element (0-g. F e has a polyatomic
40 16 interference with Ar O).
4.3.1 Blanks
In addition to contamination that rnay have occurred during sampling,
some contamination may have resulted during dilution of the samples with 2%
HNO3. As a consequence, procedural blanks were included. These blanks
contained 2% HNOj acid (with 10 ppb In as Interna1 Standard), the same acid
medium that was used for a l the dilutions.
Calibration blanks were prepared in order to detemine the "zeron point of
the wlibration. These blanks contained NASS -5, 1 OO-fold diluted. Because
NASS-5 is open ocean surface seawater, the trace element content is very low.
By diluting the seawater 100 tintes, the concentrations decrease significantly and
the samples were then mnsidered to be below the detedion limits of this
method.
4.3.2 Choice of Reagent for sample dilutions
Distilled Nitric acid (2%) is the reagent that was used to dilute seawater
samples and to prepare standards and the blanks. Nitric acid is regarded as the
best acid medium for ICP-MS because the constituent elements are already
present in the air entrapped by the plasma (Houk, 1986; Beauchemin et al.,
1988; Thompson and Walsh, 1988; Jarvis et al,, 1992).
The polyatomic ions that are fomied by hydrogen, nittogen and oxygen
are not significantly imeased by the addition of an HN03 matrix (Jawis et al.,
1992). However. other aâds, such as hydrochloric acid (HCI) or sulphuric acid
(HS04) are rarely used in ICPMS techniques. Hydrochloric acid (HCI), for
instance. is generally avoided as a reagent because CI polyatomic ions (e.g.
ArCIt , CIO+. CIOH+) cause major int-nces on the isotopes of As and V
(% and 'IV) and on many ooier trace elements induding Cr, Fe, Ga, Ge, Se.
Ti, Zn (Thompson and Walsh, 1988). Sulphuric acid (H2S04) also causes serious
polyatomic ion interferences in ICP-MS, notably on isotopes of Cr, VI Zn (Jarvis
et al., 1992). As welt, extended aspiration of dilute H2S04 leads ta severe
degradation of the nickel (Ni) sampier cones that are used in the interface region
of an ICP-MS instrument Phosphoric acid (H3PO4) behaves similarly to sulphuric
acid. The formation of poIyatornic species of P produces interferences on
isotopes of Cu, Ni, Zn and causes râpid emsion of the Ni sampler cone
(Thornpson and Walsh, 1988; Jarvis et al., 1992).
Taking into consideration al1 the above information, HNOj was chosen as
the acid medium for the work included in this study. Reagent grade HN03,
distilled in-house in Teflon stills was used for the dilution procedure.
4.4 Compensation for Interfemnces
Interferences assoaated with seawater nebulimtion into an argon plasma
during ICP-MS analysis cm be classified into two groups, nspectroscopic" and
"non-spectroscopicn (or "chernical*) interferences. The following -ans explain
these analytical problems and alço describe the p d u e s used to improve the
quality of the results of this work
4.4.1 SpeWoscopic Interferences
Spectroçcopic interfererices are caused by atomic or molearlar ions
having the same nominal mass as the anafyte isotope of interest The resuitïng
signal may disturb, or even conceal the true analyticai signal. Consequently, the
accuracy of the detemination as well as the detedion limits may be significantly
altered. The sources from which the interfering sWes may arise are many and
no generally accepted model exists to describe al1 the con!ributing factors. The
interface of an ICP-MS (the arrangement consisting of a sampler and a skimmer
cone with diameters of lmm) contribute in the generation of many different
molecular ions (Field and Sherell, 1998; Moens and Jakubowski, 1998; Field et
al., 1999).
In this study, the isotopes that were chosen for analysis were among the
ones with the highest abundance but free from isobaric overfaps (Table 4.1). An
isobaric overlap occurs when two elements have isotopes of neariy the same
mass (Jarvis et al., 1992; Reeds et al., 1994). For example, '% (relative
abundanœ 48.89 %) has an isobaric overfap with w ~ i (relative aôundance 1 -08
%), therefwe =Zn, with the second highest abundance (27.81 %), was analyzed.
Argon, hydrogen and oxygen are the dominant species present in the
plasma and these may combine, during caoling in the tail of the plasma, with
each other or with elements from the analyte matrix to form polyatomic ions.
Such ions can cause more severe interferences than the elemental isobaric
overlaps (Houk, 1986; Janris et al., 1992). In addition to Ar, and 02, other
major elements (e.g. N, SI CI) present in the solvents or acids used dunng the
sample preparation process also parüapate in these reactions. The magnitude of
polyatomic ion formation, and the rasulting interferenee po#ems depend on
parameters such as the nature of the acid and cf the sample marr# To eliminate
polyatomic interferences, isotopes with peaks adjacent to polyatomic peaks,
were analysed in this study in medium resolution (MR, m/Am=3000). A resolution
of m/Am=3000 is usually suffiCient to eliminate more than 90% of the
interferences caused by polyatomic ions (Moens and Jakubowski, 1998; Becker
40 16 and Dietze, 1997). For instance. % ~ e has a polyatomic interference with Ar O
(TaMe 4.1). The latter is a product created from the discharge gas argon and
from oxygen contained in the solvent used (Houk, 1986; Beauchemin et al.,
1988; Jarvis et al, 1992). To resolve the M o peaks completely, in this study, 5 6 ~ e
was analysed in resolution of M m = 3000. Alxi, other trace metals (=CO, '%Ji,
%ut '%I. etc) that had serious polyatomic interferences (Reeds et al., 1994;
Field and Sherell, 1998) were analysed in medium resolution. Ba and U were
analysed in both low and medium resoiuüan, but the resuits obtained from both
modes appeared to have no significant dinerem. Trace elements with very low
canœnrations in seawater, such as ' ' '~d, (0.03 ppb in unpdluted seawater)
were analysed in medium resoluüon, because even weak interferences can
affect the quality of the aquired measurements. Although using medium
resolution can be an effective method to avoid polyatomic interferences, it results
in decreased sensitivity by a factor of 73 f rm low resolution (Rodushkin et al.,
1997; Reed et al., 1994). Reduced sensitivity tenders some elements
unmeasurable (Le. below detection limits).
Table 4.1: Preferred isotopes of the major and trace elements of interest for HR- ICP-MS analysis used in this study. The most abundant, interference-free isotopes were chosen for analysis. Medium resolution was required for further elimination of potential spectral interferences.
I Na 1 23 100 Mono-isotopic Medium
ELEMENTS
MAJOR ELEMENTS
PREFERRED ISOTOPE
Mg
TRACE ELEMENTS I I I 1
S
Ca
ABUNDANCE (96)
24
32
44
Mo
COMMENTS AND INTERFEREFiCES
79
U
Cs
RESOLUTION REQUIRED
95
2.06
98
Rb
Most abundant free isotope
238
133
Li
Ba
V
Medium
Most abundant Free isotope
f'J20
23.7
85
Cr
MBdium
Medium
99.2
100
7
1 38
5 1
Cd 1 12-75
Most abundant free isotope
72.2
52
Ni
Cu
L w
Most abundant ftee isotope
Mono-isotopic
92.5
71 -66
99.76
%00, IOB?%~
%lol4bI
Low
Low
Most abundant free isotope
83.76
Medium
56 i 1 67.88
63 69.09
Medium
Most abundant fie8 isotope
Most abundant free isotope
36~ i16~
Medium
Low
Medium
QAr'%, %OH* ='=Ar0
Most abundant free isotape
NaAr, %gncl. =hAg3%rt 2%Ag~a~
Medium
Medium
Medium
Table 4.1 (con't-.- )
ELEMENTS
Refractory oxide ions, another type of spectroscopie interference, form
either as a result of incomplete diss0clSOClaüon from the sample matrix or from
recombination in the plasma tail (Thompson and Walsh, 1988). Aithough
poiyatomic interferences cause the most severe problems, refradory oxides
should be taken into account in some matrices, as well. These ions are mass
units of 16(MO'), 32(M0$) or 48(M&') above the peak of the isotope of interest
(M'). The relative level of oxides expected ean be predicted from the monoxide
bond strength of the element of interest (Jarvis et al,, 1992). For instance, in this
study, '"cd analysis suffers frorn interference d e d s due to the formation of
MoO' species (%Mo1%) and canot be resolved even by HR-ICPMS. Further,
the fact that cadmium ocairs in seamter in very low levds (Cd4.03 ppb)
compared to molybdmum (- ppb) complicates its analysis (Fiid et al.,
1 999).
Zn
Mn
Fe
Co
Pb
AI
PREFERRU) ISOTûPE
66
55
56
59
208
27
--
ABUNDANCE (96)
27.81
100
91 56
100
52.3
100
COMMENTS AND INTERFERENCES
RESOLUTWN REQUIRED
Most abundant free isotope
Na01. 4 ~ r 1 s ~ , %r14~ H
%rt60
@C~OH, ~a%, ArF,
24~gsC~, "C~F, %a0
Most abundant isotope
% g ~ , "80,
1 2 ~ ' S ~ , 1 2 ~ 1 4 ~ ~
Medium
Medium
Medium
Medium
Low
Low
In most ICP-MS techniques, the magnitude of the problem caused by
interference effects is dependent on several parameters, such as the sample
matrix (Jawis et al., 1992). The matrix interferences in this study are described in
the following section (Section 4.4.2)
4.4.2 Chemical Interferences
The high salinity and the complex chemical composition of a seawater
matrix cause specific problems in anaiytical procedures. Significant suppression
of the analyte signal is observed because of the high concentration of easily
ionised elements (Na, CI, S, Ca) as well as signal drift due to deposition of salt
on the sampler and skimmer wnes of the ICP-MS system (Beauchemin et al.,
1988; Thompson and Walsh, 1988; Moens and Jakubowski, 1998). Also, the very
low concentrations of trace elements of interest (e.g. Cd, Pb, Ni, Cu, Cr - see
section 1.2.2, Chapter 1) necessitate. along with the elimination of any
spectroscopie interferences, the tedudion of non-spectroscopie (chemical)
interferences. To overcome the tiiculties with matrix efïects in this study, both
lntemal Standardisation and calibraüon by Method of Standard Additions were
employed.
4.4.2.1 Interna1 Standardisation
The correction of one elernent using a second as a reference point is
used in ICP-MS techniques. lntemal Standardisation can be empioyed foc the
following reasons (Thompson and Walsh, 1988; Jarvis et ai., 1992: Jain et al,.
1998):
(a) To calibrate for a second element
(b) To monitor and correct for long term fluctuations in signal
(c) To rnonitor and correct for short term fluctuations in signal
(d) To correct for unspecified matrix effects
In this work, the dominant isotope of In (1151n= 95.7 %) is used as the
Internai standard in order to monitor and compensate for instrument drift and
some mat& suppression of analyte signal, 10 ppb of In was added in the 2%
HN& that was used for al1 sample dilutions and blank preparations. All the
intensities measured by the ICP-MS were nomalized with respect to In. This
element is in the central part of the mass range of the elements of interest -mm
Lithium (Li) to Uranium (U)- and is almost 100 % ionized. Also, the lisln isotope
does not suffer from isobaric overlaps. In seawater, In is present in ultratrace
concentrations so that it can be taken as absent (Onans and Boyle, 1993).
4.4.2.2 Matn'x-Adjusted External Calibration
In seawater, where strong chemical interferences occur during ICP-MS
analysis, matrix-adjusted extemal calibration is the best option far measurement
of elemental concentrations (Jarvis et al., 1992). This calibration strategy was
chosen for this work because it has produœd highly accurate and precise data
(Skoog and Leary, 1992; Rodushkin and Ruth, 1997; Field et al., 1999). The
smdards for the calibration procedure were prepared by:
taking five equal aliquots (10 gr) of the seawater from surface waters
(99.4m), from station 048 (Table 21)
adding to each aliquot increasing quantities of a spike prepared from1000
ppm ICP-MS standards containhg known concentrations of al1 the trace
elements of interest and
final dilution of each aliquot to the same mas (1OOgr).
The matrix-adjusted extemal calibration required that the matrix of the
standards be the same as that of the samples in order to compensate for the
matrix interferences.. Consequently, a seawater sample was selected for
standard addition because, in seawater, the matnx can be considered constant.
Therefore, the analyte ions in the standards were affected the same as those in
the seawater samples. For better results, the calibration standards bracketed the
concentrations expected from the analytes.
The calibration set therefore consisted of four spiked samples plus the
unspiked original sample, al1 of which had almost identical matrices. The
resulting calibration curves (one for each trace element of interest) were
produced from measured responses (counts pet second) of the solutions with
the known elemental concentrations (the prepared standards). These response
curves (Figure 4.3) were used as matnx wmpensated calibration cuves for the
remaining seawater samples.
Figure 4.3 presents graphically the abovedescfibed procedure. The
calibration curves produced, for each trac8 element, :an be qressed as the
foliawing fundion: f(x) = a x + b. The f(x) or y-dependant parameters are the
responses VI awnts per second for each eiement of interest and the x-
indqmdmt parameters are the -md demental concentrations in the original
seawater sample- It should be noted that the y values were detemineci by
subtracüng the initial blank values h m the 'nomalized' values (the values were
nomalized with respect to Indium (In)). As well, as with any linear relationship,
'an is the slope of the cunre while "b' is the intercept of the method of standard
addition curve.
The calibration Iine that is generated intercepts the x-axis at the
concentration of the element of interest in the original seawater sarnple. The x-
intercept is in the negative region because we previously assumed that the
seawater in the standards had zero elemental concentrations. Consequentiy, the
y-axis is translated to the left by a value equal to the absolute value of the x-
intercept The new calibration line is the one used to detemine the
wncentrations of the elements of interest in the remaining unspiked samples.
orighd mmplt
Figure 4.3 Matrix-Adjusted Extemal Calibration Diagram
4.5 Detection limits and Procedural Blanks
Detection limits for trace and major element analysis were determined as
the blank concentration plus three times the standard deviation of the blank for
each element. It should be noted that each calibration blank (NASS-5, 100-fold
diluted, as mentioned in Section 4.4.1) was individually prepared in the clean
lab. The blank preparation was repeated as required, during the analytical work,
Detedion limits obtained using this procedure and total procedural blanks are
presented in the following table (Table 4.2).
Instrumental detedion Iimits for HR-ICP-MS range from pglml (Le. ppt)
level (Zn, Ni at medium resolution) to fglml (Le. ppq) for analytes with no
significant interferences such as Mo and U (Rodushkin and Ruth, 1997; Field et
al., 1999). However, the pragmatic detection limits are defined by memory
effects and the laboratory blank, not by the instrumental sensitivity. Memory
effects ocair mainly due to signal enhancements from pievious sample material
remaining in the introduction system, or in the skimmer cones of the HR-ICP-MS.
Therefore, to eliminate possible memory efFects, the washing time was inaeased
from 3 minutes or less, as is nmal ly done, to 5 minutes (McLaren et al., 1993;
Field and Sherrell, 1998; Field et al., 1999).
Table 4.2 Detedion Limits and averaged Procedural Blank values (from three replicates) for major elements and trace elements of intaest. The procedural blank values that were undetected (i.e. below determination limits of the method used) are syrnbolized as BDL.
1 ELEMENT 1 DETEClïûN LIMIT PROCEDURAL BLANK 1
Mo
U
Cs
I
1 Cr 0.01 6 BDL 1
0.09
0.02
0.002
Rb
I
1 Ni 0.12 BDL 1
BDL
BDL
BDL
Li I I I 1.2 BDL
1 1 I 4
Cu
Zn
BDL
I
0.046
0.227
Mn
0.020
BDL
1 I 0.029 BDL
CHAPTER 5
Results
5.1 General
The main fows of this Chapter is to present and discuss the analytical
results obtained for the major and trace elements of interest in the seawater
samples from the Eastern Great Australian Bight (GAB). Further discussion of
these results is presented in Chapter#6.
5.2 Analytical Summary
This work demonstrates a rnethod for direct analysis of seawater by
double foçusing HR-ICP-MS. The pretreaîment of the samples was restrided to
dilution and intemal standardkation. Only one element, indium, was employed as
the internal standard of the analysis. Field et al. (1999) have previously proven
that using one internal standard in the ICP-MS analysis is sunicient to account for
instrumental drift and matrix suppression. Also, the washing time (using 2%
HNOs ) was increased from 3 min, as suggested by McLaren et al. (1993), Field
and Shemll(l998) and field et al. (1999), to 5 min in order to reduce memory
effeds (Rodushiün and Ruth 1997). Quanfjfication was obtained by matrix-
adjusted extemal calibration in order to accwnt for matrix interferences (Section
4.4.22).
The analytical precision and accuracy of the method were detemined by
analysis of three NRC Certified Reference Materials and one High Purity
Seawater (HPSW) standard. The standard deviaüon of values found in CASS-3
was used to express the analytical precision of the major and trace elements
because the seawater samples were collected in a coastal environment rather
than in the open ocean. As a result, these œrtified concentrations were used in
al1 comparisons with the elemental values obtained from the wllected samples.
The precision is expressed in ternis of relative standard deviation or RSD. The
RSD is given by:
Standard Deviation (10) IOON RSD = (Eq'n 5.1) Mean Value (GiII, 1997)
Graphically, throughout this thesis, the precision is indicated as:
Measured value
Minimum value Maximum value
Accuracy was determined using certified values (CRM), available for some
trace elernents only. Published values for HPSW are presented in Table 5.1 for
cornparison with the values found for the major elements, as no certified values
are available. The accuracy is given by:
Mean Value - Certifiai Value loOO/o (Eq'n 5.2) Accuracy = Certified Value
(Gill, 1997)
5.3 Analyücal Results for Major Elements
Three reference materials were analyzed for the validation of the major
elements analysis (CASS-3, NASS-5 and HPSW). The results are pceserited in
Table 5.1. Na, Mg, Ca and S exhibitecl very good adyücal precision.
28% and 5.4% (RSD). Cornpad to the HPSW puMished values, the
concentrations measured for Na, Mg, S and Ca in HPSW demonstrate good
agreement (within l a or 0.5% RSD).
Table 5.1 CASS-3, NASS-5 and HPSW analytical results for the major elements of interest
1 Found values represent the mean values of 10 replicates for each element The values in parentheses show the standard deviath (la) of the mean value.
2 HPSW published values are provided by www h sw ca. These concentrations were measured in seawater that has been prepared h m hiph p?riiy-ymeiars, sab and oxides.
5.4 Major Element concentrations in the Eastern GAB seawater
The major element concentrations measured in the seawater samples
from the Eastern Great Australian Bight are presented in Tabie 5.2. Na, Mg, S
and Ca show reiativeiy uniform concentrations wi# depth. The mean values
obtained for these elements, from the analysis of all 63 seawater samples, are:
Na, 1 1851 ppm (+1- 4%); Mg, 145ippm (+/- 3%); S, 104lppm (+/- 3.6%) and Ca.
491 ppm (+1- 5%).
Table 5.2 Analytical results obtained for the major elements of interest in the seawater samples fram the Eastern Great Australian Bight. The demental detedion limits of the method used are also presented. The sample numbers provide information on the station and the depth each sample was collecteci fram (Le. SVVT00ff3 is the sample collected fram Station 007, at 3m depth).
ELEMENTl SAMPLE Mg (ppm) S (ppm) Ca (ppm)
Table 5.2 (con't ...)
ELEMENTI SAM PLE
SW48 99
W49 82
SWr49-2
SWT49-72
SWT50-63
sWrS1-44
SWT52-37
S m 3 5
SWT53 IO0
SWT53 ,120
SWT53 196
Na (ppm)
12298
12275
13061
12555
13013
11935
12094
11708
12069
1 1768
1 1633
Mg (ppm)
1 470
1402
1591
1462
1579
1433
1418
1 376
1378
1409
1350
S (ppm)
1114
891
1192
1125
1124
1033
1056
987
883
1020
855
Ca (ppm)
520
463
548
487
498
475
487
470
496
435
482
5.5 Analytical Resutts for Trace Elements
As discussed previously, the analytical preüsion and accuracy of the trace
element direct seawater analyses (in this study) were detennined by the analysis
of the NASS-5, CASS-3, SLEW-2 certified reference materials- The results are
presented in Table 5.3. Measurement of concentrations of 17 dissolveci trace
elements in NRC certified reference seawater (CASS-3) demonstrates very good
reproducibility for Mo, U, Cs, Rb, Ba, Cr, V and Mn. The analytical precision (+/-
la) for these elements was l e s ~ than 10% (RSD), except for V (14%) and Cr
(16%). Further, measured values for Mo, U, V and Mn show very good
agreement with certified and previously published values (within 95% confidence
Mt ) . Figures 5.1, 5.2 and 5.3 present graphically the relationship between the
CASS-3 certified values (available for some elements only) and the CASS-3
concentrations that were obtained for each element by the application of the
method used.
The analytical precision for Mn, V and Cr are comparable to the values
obtained by Field et al. (1999). They demonstrated a direct seawater analysis
with overall precision (la) of 3-1 0% for these elements 4 t h the exception of Cr
(16%)- and good agreement with certified (CASS-3) values (Section 3.4).
The detedion limits for these trace elements were: Mo 0.09 ppb, U 0.02
ppb, Cs 0.002 ppb, Rb 1.2 ppb, Ba 0.04 ppb, Cr 0.016 ppb, V 0.03 ppb and Mn
0.029 ppb (Table 4.2). During the laboratory preparation of the samples, the
procedure biank values for these elements were kept at a very low level - ewept
for V, which had a blank value of 1 ppt or 0.OOlppb (Tabie 4.2)- Fe, Co, Ni, Cd,
Cu and Zn analyses were less mse (Table 5.3). The determination of Pb, Al
and Li needs to be further investigated, as well.
Conceming the anatytical challenges associated with the determination of
40 16 Fe in seawater, Moens and Jakubowski (1998) have reported that Ar O'
interferes with the analysis of % ~ e + and that a resolution of at Ieast 2500 wauld
0 1 2 3 4 5 6 7 8 9 1 0
CASSS Found values (ppb)
Figure 5.1 CASS-3 Certified Values versus CASS-3 Found Values for conmative etements Mo and U.
O Cd i 2 3 4 5 CASS-3 Found values (ppb)
Figure 5.2 CASS-3 Certified Values versus CASS-3 Found Values for recycied elements Ni, Cu, Cd, V, Zn, and Cr.
Figure 5.3 CASS-3 Certified Values versus CASS-3 Found Values for scavenged elements Co. Fe. Mn. Pb.
be suffident b resolve these spectmapic interferences tom the analyte peaks.
Rodushkin and Ruth (1997) and Field et al. (1999) also suggested the use of
medium resolution to eliminate al1 rnatrix and plasma based interferences (such
as %a0 and 2%dg"~) associated with seawater nebulization into the argon
plasma. Consequently, in the curent investigation, Fe was analyzed in medium
resolution (mlAm=3000), to avoid polyatomic interference effects (also discussed
in Section 4.4.1). However, the analyüwl preasion (la) of the analysis,
assessed as 33% (RSD), could be further improved. Previous research published
by Fumess and Rainbow (1990) and Field et al. (1999) indiwte that a possible
reason for the degradation of the Fe analytieal quality is that Fe is one of the
most easily cantaminated trace metals.
Co is present in seawater in very low levels (CASS-3 certified value for Co
is O.MI ppb) and its determination can be generally challenged by various
parameters such as spectral interferences and instrumental sensitivity.
Rodushkin and Ruth (1997) have reported that Co analysis, in seawater, sMers
from a number of unresolved spectral intderencao, such as SU OH. *c~F.
%a0 and 2 4 ~ g " ~ ~ . To reduce the effeds of these types of interferences in the
Co analysis, this element was scanned in medium resolution (Field et al., 1999).
However, the HR-ICP-MS sensitivity decreased by a factor of approm'mately 13
when the redution increased from low to medium mode (Radushkin and Rutfi,
1997). Considering the Iow ancentration of Ca in seawater. the decreas8 in
sensitivity may have affeded the quality oF this elmental ariaysis, leading to an
analytical preclreclsion (1 a) of 29% (RSD).
Cd is another element that occurs in a very low levels (0.030 ppb) in
seawater- The determination of this trace dernent can be readily affected by
spedral interferences or contamination, due to its lm concentration. To reduce
possible isobaric interference efFects, Cd was scanned in medium resolution, as
suggested by Rodushkin and Ruth (t997). However, the results for Cd analysis
showed a precision (la) of 45% (RSD). It is believed that, in this work, the
interference of %Io0 hindered Cd acaaate analysis (also diswssed in Section
4.4.1). Cd was analyzed in medium resolution. Hawever, "MOO interferences
were not eliminated. Accarding to R e d et al,, (1994) these interferences cannot
be resolved even at high resolution. Further, the sample introduction system,
which comprises a standard nebuliser and a spray chamber supptied with
Elment 1, may have significantly affected the sensitivity of the HR-ICP-MS
concerning the Cd analysis. Field et al. (1999) reported that the use of a
microconcentric desolvating nebulization, coupled with a shielded torch and
typical hot plasma high resalutiwi ICP-MS, reducsd Mecüvely the %bO oxides
(by tv,m orders of magnitude) and led to a lO-fold enhancement of sensitivity
above the standard spray chamkr. Consequentiy, the Cd determination in
seawater can be further improved by optimizing the sampie introduction system
along Ath spectral interference and contaminath cmtrol.
High Zn results, compared to the CASS-3 certified values, may have been
caused by the presence d P$ in the seawatef rnatrix of the samplaa. This
spectral interference cannot be resolved by medium resolutiori analysis (Red et
al, 1994). Accurate determination of Zn may have also been hindered by its kw
concentration levels and insuffident intemal standardization. This phenomenon
has been previously observed and reported in the Iiterature (Rodushkin and
Ruth, 1997; Field et al., 1999). The analytical precision (la) for Zn were
assessed as 34% (RSD).
Similarly, Ni and Cu were analysed in medium resolution to avoid possible
isobaric interferences, as suggested by Janris et al. (1992), Reed et al. (1994),
Rodushkin and Ruth (1997). As well, Ni blanks derived from nickel cones were
eliminated by using Al cones. However, Ni and Cu analysis exhibited low
precision (la), 44% (RSD) and 46% (RSD) respectively. Procedure blank values
for Ni and Cu were kept low (Table 4.2). However, the estimated detedion limits
for Ni were high (0.1 19 ppb). Both elements are reported by Field et al. (1999) to
be abundant in laboratory and instrument materials as well as in anthropogenic
aerosols. This results in higher contamination nsk for the determination of Ni and
Cu. Further improvement of laboratory procedures will probably optimize the
analysis of these two elements.
Analytical results for Pb showed that the procedure blank values for this
element (0.024 ppb) were high (Table 4.2). Consequentl y, Pb determination
gave low precision and accuracy (Table 5.3). Li and AI direct determinations in
seawater wuld be improved, as well. In this study, both elements gave poor
precisions in their results (Tabie 5.3). These trace elements (Li and Al) have low
atomic mass (7 and 27 respecüvely). Accarding ta Janris et al. (1992) and
Pupyshev et al. (1999), analysis of elements with low atomic mass c m be
hindered by mtrk interference Mects. This argument is illustrated in the
following figue. wtiich shows a response curve of the HR-ICP-MS. This wnre is
a graph of intensityf-on (Le- instrumental response) versus the mass to
charge ratio of each element. Profoundly, the response measurements for Li and
Al can be significantly altered by the background signal fiuctuations of the
instrument. On the other hand, the response for U, which has a higher atomic
mass, is less Mected by the instrumental noise (Figure 5.4).
Instrumental Response
(COU- ~ ~ e ~ - ? p p b ) Background : i : : ! i : :
signal . . : > . . I I I i ,
Li Al In U
Masslcharge @aitons)
Figure 5.4 This double-focusing ICP-MS Response Cuwe shows that the instrumental responses for Li and Al, which have low masslcharge ratio, are challenged by the background signal.
Table 6.3 CASS-3, NASS-5 and SLEW-2 analytical results far the trace elements of interest,
0 I I 1.95 6.23 Q.6 5.50 MO O.@# -14.3% 1% 8.22% 6% 3.7'
(0 (0 .w (0.09) (1 .O) (0.35) -. -. ..--.
2 71 2'77 7.6%
1.81 U 1% 2.84' 2.6' 10% 1 .T
(0 21) (0.21) (O. 18)
ol'a
2.75 0.148 0.066
Ca 2.6% 50% (0, 'w WoM) (0.044)
87.3 89.6 32.8 Rb 10% 7.5% 32%
(9-0) (6.7) (10.7)
40 33 35 U 91 % 95% 105%
1 1 (37) 1 I I I 1 (31) 1 I I 1 (37) 1 I I
1.2'
0.1 10
(0.01 5)
0.102
(0.039)
2%
9%
14%
58%
28%
low
0,092
(0.00s)
1 .24
(0.25)
1.7%
14%
I 6%
34%
Ba
V
- Ln
553
(OJW
1.14
(0.16)
0,181
(0.028)
4.598
(1 572)
1 .50
(0.1 5)
16.85
(3.39)
1.94
(O. 15)
0.284
(0.033)
3.1 75
(0.301)
20%
8%
11.7%
0.6%
0.169
(0.01 8)
1.10
(0.1 4)
75%
low
a%
low
4.00
(0.08)
1 .24
(0.1 1)
0.1 41
(0.020)
4.886
(2.Q13)
Elrmrnt
NI
.-- .
Cd
' Found valuer represent the mean values of 10 replicabs (n=10) for each element. The values in parentheses show the standard deviation (la) of the mean value.
Certlfied values are provided by NRC, The values in parentheses are the uncertainties expressed in 85% confidence intervals CASS-3 publlshed value for V was obtained from Chapple and Byme (1996). Accuracy determlned as over 100% is indicated in the Table as "IoW.
* Information values only, provlded by NRC,
cAsm Fwnd Vdurr
(Ppb)
0.93
(041) .-.-W.-
0.32
!O 16)
46%
0.QW
(O.m7)
0.01 1
(0.003)
0.207
(0.035)
0.008
(OJW
@%
85%
42%
lOW
8.6%
a%
33%
160%
64%
0.880
(0.1 16)
0.037
(0.01 4)
0.958
(0.029)
0.043
(0.023)
0.256
(O. 1 00)
RSD
W
--
44%
45%
0.61 7
(0.062)
4%
low
low
lOW
2.51
('JW 0.041
(0.OoQ)
126
(0.1 7)
0.012
(O.oW
13%
37%
85%
53%
39%
Catifiad
vdueo
(Wb)
0.388
(0.082)
0.030
(0.005)
low
26.2
(1 4 0.148
(0.01 3)
4.087
(0.323)
0.145
(0.209)
0.252
(O. 153)
Pulkhod valuhi
(PPb)
0.870
(0.341 )
7%
9%
8%
144%
60%
Accurmy
(%)
low
low
39%
17.1
(1.1)
0.056
(0.Ow
2.37
(0.37)
0.027
(0.006)
S3%
low
72%
kW
Fwnd valu-
(Wb)
0.76
(0.44)
0.33
(0.1 71
0.297
(O.oW
RSD
(%)
58%
50%
low
Cetllfled
values
@Pb)
0.253
(0.028)
0.023
(0.003)
2.702
(1.020)
Acouraoy
(%)
low
low
98% 37.7%
Found values
(Wb)
1.53
(0.21)
0.30
(0.09)
1.62
(0.1 1)
RSD
(%)
Certmed value8
(Wb)
Accunoy
low
low
- - - - - - - --
14%
29%
0,709
(0.054)
0.019
(0.002)
5.6 Trace element concentrations in the Eastern GA8 seawater
The trace element concentrations measured in the seawater samples from
the Eastern Great Ausfralian Bight are presented in Table 5.4. Mo, U, Cs, Rb
show relatively constant concentrations with deph. The average values for these
elements are: Mo, 10.iOppb (+/- 0.9% RSD]; U, 3.32ppb (+/a% RSD); CS,
0.1 80ppb (+/-2.7% RSD); and Rb, 1 09.2ppb (+/-IO% RSD). Li would be expected
to behave canservatively, as well. However, its concentrations show low
precision for the reams that were discussed previously in Section 5.5. As
diswssed previously, the seawater samples were colleded fram surface (O-
200m) and intemediate (200-991m) water layers of the area of research. The
variations with depth in the concentrations of the recyded and the scavenged
metals of interest are presented in TaMe 5.5. Arnong the recycled metals, Ba
shows a surface depletion foltowed by an increase in concentration with depth,
whereas V and Cr reveal no depthelated patterns. in, Cd, Cu and Ni
demonstrated high RSD in their analyses. fherefore, m i r results should be
viewed with caution. It should be noted that during the analysis of the seawater
samples from the Eastern GA6 ara, Zn levels in samples 032 to 057 (Table 5.4)
were below detedion limits of the method used
Mn surface concentrations show a sIigM decrease compared to deeper
waters. On the basis of the present data, as it will be furthet discussed Iater in
this investigation, Mn does not show the distribution of a typicd scavenged
metal, although its behaviour is predided to be of that type. Co and Fe
concentrations show no variation with depth, eioier- Due to their iow analytjcal
precision, the geochemical profiles of Fe and Co, Ai and Pb, are hindered. Mn
values obtained for the seawater samples h m GAB were close to the Mn
detection limits (Table 5.4). Consequently, the elemental concentrations that
were beIow the estimated detedion Iimits were not inciuded in the interpretation
of the Mn distribution in the Eastem GA0 (Table 5.4). As well, Al concentrations
in seawater samples from stations 032 to 057 were not detectable.
Table 6.4 Anslytical results for the trace elements of interest in the seawater samples from the Eastern Great Australian Bight. In total, 63 aempler wem analyzed. The sample numbers provide information on the station and the depth from which each sample was collected (h, SW007-3 is the sample colleded from Station 007, at 3m depth). The three groups of metals (consenrative, recycled and scavenged) are sepamted by double lines. The v a b s that w r e below the detection limits of the method used are included as BDL, The Mn concentrations in SWT022-70, SWTO23-45 and SVVT025-3 are exceedingly high, due to contamination masons probably, and they are not included in the estimations of aie mean value for Mn. Similarly, Zn concentrations in SVVT007-40 and SW007-135 and Cu concentration in SW53-190 were not included in the estimations of the mean value of these two elements.
Table 5.4 (con't . . . )
Table 6.6 Recycled and scavenged rnetal mean concentrations measured in samples from surface and intemediate seawater layers of the Eastern Great Australian Bight. In total, 63 samplas were analyred (n=63).
ELEMENT 1 Depth O-2ûû m Oepth 200-991 m RSD
Recycled Metals
Soavenged Metals
1.7%
14%
16%
34%
44%
45%
5.01
1.65
0,231
4.574
0.929
0.353
Ba V
Cr
Zn
Ni Cd
6.5%
299'0
33%
64%
150%
4.77
1 .61
O Z ! 1
2.590
0.724
0.321
0.214
0,029
1,124
O, 22
0.108
Mn CO
Fe
Al
Pb
0.195
0.031
1.209
0.26
0.137
CHAPTER 6
Discussion of Results
6.1 General
The focus of this chapter is to discuss and analyse the results obtained
from the method used to detemine the elemental concentrations of 17 trace
rnetals and 4 major elements. This ctiapter is broken down into two parts:
P Part 1 wiil attempt to provide a rational (based on the results) in order
to link al1 the data avaikble for this region and provide a better
understanding of the oœanographic environment in Eastern Great
Australian Bight. The area of research is examined firstly as a whole,
regarding the physical oceanogtaphic information. Secandly, the
physical oaanographic charaderistics of the region are melateci to
the elemental analyücal results obtained.
P Part 2 will explore the parallelism betwmen the findings in the Eastem
GA0 area and two ottier regions, namely, the Mediterranean Sea and
UleNrnAtraiticOcean
6.2 General Discussion on Eastern GAB Oceanognphy
The information that was derived by the nutrient distributions, the
temperature - salinity levels and the elemental concentrations of the colleded
samples in the Eastem GA0 leads to several observations about the
oceanographical dynamics of the area.
As reported previously (Section 2.2.6), the GA0 region is characterized
by three major currents:
The GA0 Plume, which is a wam, nutrient depleted and very highly saline
(higher than 36Olm) seawater mas that oaws in the central and eastem part
of the Great Australian Bight (Rochford, 1 984; Rochford, 1 986; Longhurst,
4 998).
a the coastal airrents, known as Leeuwin Curent and South Australian
Current. Leeuwin Current is a warm, low in nutrients water mass with a
salinity range between 35.8oo0/m and 35.@la, (Gersbach et al., 1999). This
Current appears in the GAB region during the austral fall (April-May), flows
eastward and becornes stronger in the winter. South Australian Current (SAC)
is also warrn but with higher salinity water body. SAC is fomed during the
summer months and flows eastward.
The Flinders Current, which is a cold, nutrient rich water body. This wrrent
occurs in deeper waters than the abovenientioned coastal GAB wrrents and
appears dose to the coast during the au- sunmer.
Thie followïng sections will look inbD the presence of the abovemeritioried
water masses in the area of research by correlating the analytical results
obfained for the major elements and trace elements of interest with the physicd
charaderistics of the seawater samples at the time of their collection. Table 6.1
presents the temperature, salinity and nutrient values measured at each station,
during the FR 03/98 mise (Figure 6.1). The water samples were collected in
Niskin bottles, at various depths, during each conductivity-temperaturedepth
(CTD) cast Temperature and salinity were measured with a themosalinograph.
Nutrient concentrations were measured with an autoanalyser (using a
colon'metric method), which gave precisions of: Nitrate, 0.98%; Phosphate, 0.9%;
Silica 1.48%.
Table 6.1 Description of 63 seawater samples collected in the region of study (Eastern GAB). The coordinates define the position of the stations on the map (Figure 6.1). The sarnple numbers provide information on the station and the depth eaeh sample was wllected from (Le. SVVT007-3 is the sample coilected from Station 007, at 3m depth). The values that were below the detection limits of the method used are indicated as BDL.
Phoqhsta ma)
0-14
0.14
0.30
0.50
. 0.62
Coordimbs
37 53-37 s
139 53.88 E
Dspai (4
3.7
40.3
65.4
135.5
2212
3 7 1 I a S
138 56.35 E
Station
7
7
7
7
7
291.1
3.3
265.5
Tempenture CC)
17.56
16.89
13.89
1251
1201
Sampks
S W W 7 3
SWOO7 40
SWm07 65
S m 7 135
SWTOO7 221
7
9
9
11 -61
1820
Salinity ekd
35.161
35.323
35,122
35.174
35.093
SWTOO7 291
sw'roo9 3
SWTOOS 265
35.- 1 8 2-03 0.69 i
! 3â282 ' - - -
12.57 1 35.151 / 6.02 1 1.74 1 0.55
N i ma)
BOL
BOL
124
5.41
7.36
Silica oimow
0.63
0.74
0.95
1.63
1.95
Table 6.1 (con't.. . )
N i i mow -
- 3.07
BOL
0.15
6.31
BOL
BOL
BOL
6.88
BOL
BDL
1.81
4.28
12.1 1
3.61
BDL
4.99
2.36
Table 6.1 (con't ... ) -
Coordinates Station Sampks ûepth T m n k i m Saîinity Nitrate Silica Phosphate (ml cc) e100) WOW ~ O V L ) mou^)
34 m.67 s 32 S W T ~ ~ 4 4.3 20.88 38.132 BDL 0.41 0.03
132 23-58 E 32 SWT32124 124.1 14.55 35.938 1.90 1.35 0.31
32 S W 3 2 247 247.9 12.94 35.254 6.39 2.00 0.56
32 S W 3 2 4'78 476.1 9.91 34.797 14.91 4.01 1 -05
33 ûô.98 S 37 S m 7 3 3.1 19.79 35.798 BOL 0.56 0.08
13306.03 E 37 Sm37 75 75.8 16.08 35.709 1.91 1.83 0.30 t
Table 6.1 (wn't ... )
5.4 20.53 36.002 BDL 0.57 0.05
190.4 13.37 35.505 4.40 0.92 0.44
Figure 6.1 Map of the FR 03/98 Cniise in the Eastern Great Australian Bight in March-April 1998. The lOCaff*on and the number of each station ( h m 007 to 057) are labeled on the map. The direction of the mise was east - west. The dashed Iines indicate depth contours of aie oceanic floor.
Some general observations about the region of shidy can be d m
by ttie cornparison betwwn temperature and salinity vs depth in the
Eastern and Central GAB, stations 007 to 023 and 025 to O 5 7 respedively
(Figures 6.2 and 6.3). Notably, surface temperatures (at 2-5 to 5.4m depth) are
relatively high, (between 17.20°C and 20.90°C). Surface salinity values, though,
Metms below sea ievel
Figure 6.2 Oiagram s M n g the variations of salinity (measured on the dght y-axis) and temperature (measured on the kit y-axis) versus depth ( x-axis) in waters from the Eastern part of the study area (staücins 007-023). The surface temperatwe of the regional waters is high. due to warm air temperatures of the season (MarctEApril). The enhanced salinity values of th surface waters are a resuft of evaporation proceses. Ihe low saiinity value of 32.380 Olm. show at aie bottom Mt of the graph, is due to mMng of fresh water from the coast (riverine ?) with the oceanic water.
Metres below sea level
6 ' A T '
figure 6.3 Graph stiowing tM Temperature and N i n ÿ bistributions {on the ri@ and left -s * )muidepln(x-aias)ùiwatersfcomtheCentralpaRofttiesbdyareaandinMSpencerW
=%lm. Rie simm mnky vâiües h Uw, Central GAB encwd h. 36.&lm M. implying the presence of the GAI3 Pkime water mass. In deeper waters (in mis graph, until4Mlrn depüi), the sdhiity and temperatwe sigrtatures menMe to the Eastern part d the GA8 (Figure 6.2).
appear to be elevated in the Central part of the GAB relative to the eastem part,
Specifically, in the Central GAB, salinity values at 2.5 to 5.4m depth exceed
36.000 ' lm and temperature ranges behveen 17-80 and 20.90 OC (Figure 6.3). In
the Eastern GAB, though, salinity levels at similar depths are generally lower
(between 35.1 00 and 35.400°/m) and temperature values range between 17-50
and 18-70 OC (Figure 6.3). The temperature diirenœ between the two regions
is due to dimatic as well as oceanographic parameters that influence the
temperature signature of the GA8 marine environment, The warrn surface water
temperature across both areas of research is attn'buted to the seasonal air
temperatures that occuned within this region pnor to the time of the sample
collection. The FR03198 cmise in the GAB took place in the austral late summer-
early fall (March-April). As described in Secüon 2.2.4, the coastal climate of the
GAB is charaderized by hot, dry surnmers. Consequently, the air temperatures in
the region were warrn during the late summer - early fall (previously discussed in
Section 2.2.7). Additionally, wam remnant Leeuwin Curent water that may flow
in the area contributes to the high surface seawater temperature.
The difference in surface water salinities between the Eastern (stations
007 to 023) and the Central part (stations 025 to 053) of the area is also a
fundion of climatic and oceanographic parameters. Firstly, the high seasonal air
temperature causes evaporatim and elevated salinity levels on the GAB surface
-terer Corisiden'ng the very Icm pmcipitatim rate in South Australia during
the smmer time and the regïumi de- in ftesh water sources, the
evaporatiori praeesses cm significantty inmase the level of salts in the coastal
seawater of the GAB region (Sections 223 and 22.4). Secondly, diierent
oceanic currents affect the two regions (Eastern and Central part). The Eastern
part is more infiuenced by the presence of cold, low salinity water masses, as
described from the available data in Table 6.1. The Central part, however, is
affected by the warrn and saline water bodies of the GAB Plume and remnant
Leeuwin Curent waters, espeaally in tfte surface and subsurface water layers,
as reported by Rochford (1984), Gerbach et a[. (1999) and James et al. (2001).
Figures 6.2 and 6.3 also indicate that below 220-250m depth,
temperature and salinity values decrease within the enüre area of interest. The
temperature values are less Vian 12.00 O C and the salinity is below 35.200 Ola.
The closest oceanic source with comparable temperature and salinity is the
Southem Ocean water (in this thesis is msidered the same water mass with the
Intemediate Antarctic Water) whibi has a salinity of less Vian 35.500~1~ and a
temperature that can be as low as 4.00 OC, as reported by Gerbach et al. (1999).
ConsequenUy, this water mas may originate from the Southem Oœan. When
this water body moves towards the shelf, then it is referred as the Flinders
Curent, as reported by Longhurst (1998) and James et al. (2000).
The Central part of the area of research exhibits high surface salinity
levels, due to warrn air temperatures and intense evaporation processes. These
characteristics are more pronounced as seen in the values measured at 032 (at
4.3m depth), 048 (at 3.7m depth), 049 (27m depth) and 053 (at 5.4m depth),
where salinities range between ~ - 0 O C f f ~ and 36.17@:= As discussed peviou*.
this warm surface seawater may extend eastward, until t h location of stations
015 and 016. The cold Southem Ocean-originated water body underlines ail
surface and intermediate currents in the region of study.
The salinity levels in the Spencer Gulf are the highest in the area of
research as seen in Figure 6.4. This is the result of intense evaporation on the
surface waters of the Gulf, which is a seasonal phenornenon, mainly during
Austral summer and autumn. As was mentioned in Section 2.2.4, the coastal
climate of the region, where this Gulf is located, is hot and dry. These climatic
features affect the surface seawater chemistry of the Spencer Guif seawater by
causing evaporation and inueasing the salt concentrations. Also, due to the
regional topography, the seawater locked in this Gulf is isolated from the water
currents that circulate in the investigated area. As a result, evaporation is
possibly the primary parameter responsible for the elevated salinity and
temperature values measured at stations 055,056 and 057 in the Spencer Ouif.
Station 054 is located outside of the Gulf (Figure 6.1). The surface
temperature value of this station is lower than the correspanding values
measured at the stations in the Gulf (Figure 6.4). As weil, the surface salinity
rneasured at this station is significantly lawer than at the stations 055, 056, 057.
Consequentiy, the surface seawater at this station is less affeûed by evaporation
processes. At the depth of 96m, information from 054 station shows that the
water temperature and salinity are significantly decreased and the nutrient levels
are high. This is the result of the intrusion of a cold, nutrient nch seawater m a s
in this area, undemeath the surface seawater.
8 Station 057.40rn
m o n 0 ~ . 4 r n A Station Q ~ s . z & ~ A Station 056.45rn
Eastern GA0 i Central GAB & Spanœr Gulf
3 32 33 34 35 36 37 38
Salinity &J
Figure 6.4 Temperature vs Salinity correlation in waters from al1 stations in the area of research. The enhanœd temperature and salinity Ievels in the Central GA0 waters are evident on this graph, compared to the Eastern GA8 waters. Spencer Gulf seawater exhibits the highest saiinity ievels.
6.3 Nutrient Distributions Across the Ama of Research
The distributions of phosphate, nitrate and silicate in the area of study
are presented in the following graphs (Figures 6.5.6.6 and 6.7). Surface nutrient
concentrations (between O-1OOm depth) appear to be enhanced in coastal
stations 010, 016, 022, 039, 051 and 052 (Figure 6.1) where nitrate, silicate and
phosphate concentrations are comparable to deeper waters, below 200m depth,
where cold, nutrient-rich water from the Southern ûcean occurs. Consequently,
deeper water rises and reaches the seawater surface, influencing the nutrient
contents of the above-rnentioned stations. This mixing of waters is faciîitated by
regional strong winds that displace the coastal surface water, as the Eastern
GA6 is a stormdorninated region (Longhurst, 1998). The resulting "gap* is filled
by the sub-surface water, which is colder, with lower salinity and high nutfient
level. This phenornenon is called upweliing (Broecker and Peng, 1982; Libes,
1992; Sdiurnann, 1999). The occurrence of coastal summer upwelling in the
region of the Eastern GA6 has been reported by Rochford (1984) and Longhurst
(1 998).
Below 200m depth, nutrient concentrations show a pronounœd increase
with depth. This is due to the presenœ of the Southern Ocean-originating
Flinders Current at this depth. The cdd, dense and nutrient rich water rnass from
the Antarctic Ooean irrtnides the GAB marine environment and influences the
nutnent levels
Phosphate Concentration (micromoVt)
Figure 8.5 Phosphate concentrations of GAB seawater. The phosphate concentrations inaease wiih depth. Surface waters exhibit enhanced concentrations (up to 0.65 pmaUL at 37mdepth-s&tiari052)duetoupwellingphename~dosetothecoast
Nitrate Concentration (micromoUL)
Fium 6.6 Nitrate ammtmîbns d GAû seamter- Nilrate le- hxease with deplh. Sufaee waters mkded fr#n nemtm! sWbm (Le. station 010, 016, 022) have hgh tmmhtions (betwaeri 5 - IûpmN).
Silica Concentration (micromoi&)
1 4 &Mon 05237mdepîh '
Station 051,44m dapoi Station 039.24m ciopth
Figum 6.7 Silica concentraüms of GA8 seawater. Silica contents appear to have a uniform concentration up to 2û0m depth. In deeper waters, sitica levlels increase significandy. S u h œ water silia concentrations in some coastal stations reach high levels (up to 7.8 pmolK at 37m depth - station 052).
6.4 Ins hore-ûffs hore Station Correlations
Temperatures and salinities in waters colleded from the Central GAB area
indicate that there is a shallow, wann and highly saline water mass that can be
traced up to 300 km distance from the coast. This obsewation results from the
information on the temperatures and salinities of the waters collected from
stations 050 to 053 (Figures 6.8 and 6.9, respectively) and from stations 044 to
049 (Figures 6.10 and 6.11). High temperatures, between 20.53OC and 20.94OC,
and high salinities, between 36.000~/~ and 36.15û0/,,,,, were measured in shallow
waters (5.449m depth) colleded from offshore stations 053 and 044. These
stations are located at - 250-3Wkm ftom the mast (Figure 6.1). Sirnilarly,
temperatures between 20.91°C and 20.7S°C and salinities between 36.16û0/00
and 36.090~/~ were measured in inshore stations 048 and 049 at 3m and 2m
depth, r e ~ ~ v e l y . Stations 048 and W9 are at a distance of lûûkm -12Qkm
h m the coast. Consequently, the surface temperatures and salinities in the
Central GAB region are elevated, regardless the proximity to the coast. As well,
the characteristics of this water mass that occupies the Central GA0 area, as
described by the information from stations 044 to 053, resemble the GA0 Plume
signature which is also defined by surface seawater temperatures higher than
20% and saliniües exceeding the 36.000~1m level (Secüon 226.1).
Further, seawater samples collected ftom stations 048 (at 99m depth), 049
(at 72m and 82m depth), 050 (at 64m depth), OS1 (at 44m depth) and 052 (at 37m
depth) al1 have similar temperatures (16.80-18.00"C) and salinities (35.900Olm)-
These features resdt ftom the presence of remnant LC water in this part of the
1 Figure 6.8 1
Saiinity (Oi,)
GAB. It is mentioned that the Leeuwin Current water body is warm (-19.00°C),
has lower salinity (35.800~lm -35.900~1~) and inRuences sbongly the GAB
oceanography in austral winter (Section 2.2.6.2).
The GAB Plume water mass proceeds eastward, as indicated by the
temperature and salinity profiles of surface waters collected From station 032
(Figures 6.12 and 6.13). These waters exhibit similar temperature (20.87°C) and
salinity (36.130~100) with the surfaœ waters colleded at stations 053 and 044, as
descfibed above. Station 032 is located at a distance of -300km from the shore.
Surface seawater at station 037 (also presented in Figurer 6.1 2 and 6-1 3)
exhibits warm temperatures (at 1 9.70°C) and relatively low salinity (at 35.800°1~).
These water characteristics continue to appear at intermediate depth (75.8m),
with a decrease in temperature, due to mixing with colder waters. Because of its
Iow salinity, this water mass does not belong to the GAB Plume. Its features
resemble those of waters ffom the Leeuwin Current (LC) (Section 2.26.2).
Supposing that remnant LC water moves eastwards and mixes with the GA8
Plume during the austral fall, thsi. the position of the station 037 could be on the
path of this water mass. Low salinity (35.500 - 3 5 . 6 ~ ~ 1 ~ ~ ) shallaw waters
combined with warm surface temperatures at stations 039 and 041 indicate the
existence of upwelling and mixing phenomena near the wast
Surface waters collected from station 025 have high temperature and
salinity, similarly to those of surface waters from station 032 (Figure 6-14 and
6.15). At the surface (3.7m depth), the temperature reaches M"C but the salin@
level has decreased to 35.800~/~.This wuld result from mixing of the highiy saiine
-1m - F'cgucw 6.42 rnd 6.13 Tmpera(ure and sduiity depth profiles at 032 to 041. High tempetanires and salwties eharaderire the sufaœ wabf layen in coastâi (a39 and 041) and offshore (032) stations. These staüons are an the same ûansect (Figure 6-1)-
- - -
6-U rd 6-45 Tsinparalue and tdriay prdiks a stations 017 to 025 Higr rerrpaab.ss and E e l i i îhe suhœ mtef layc~s in coastal (OZ? and û23) and dbtme (O17 ad û25) müons- These smïons are on aie same transed (Figure 6.1 ).
GAB Plume with the less saline remnant LC water mas, as both water bodies
flow eastward during the austral fall (previously discussed in Sections 2.2.6.1
and 2.2.7). At a depth of 439m, the low-salinity, cold and nuttient-rich gyral
curent (Le. Flinders Current) can be traced in waters collecteci from station 025.
Information from this station shows that the temperature and salinity gradually
decrease with depth and there is no evidence of upwelling. Surface seawater
temperatures and salinities at stations 022 and 023 are lower, due to coastal
upwelling of cold, low-salinity water that originates from the Southem Ocean.
Warrn, saline surface waters continue to ffow eastward, thrwgh station
017 (Figure 6.14 and 6.15). Temperatures and salinities are lower compared to
surface waters from the abovementioned offshore stations 053, 044, 032 and
025. This shows that the water mass that is made up of the GA6 Plume waters
and a wmponent of the LC waters becornes cooler and less saline as its
distance ftom the source (Le. the Central GAB area) increases.
Surface seawater samples wllected from stations located at the
easternmost part of the area of research (Figure 6.1) exhibit low ternperatures,
between 13.6û"C and 18.7(PC, and low salinities, ranging frorn 3 5 . 0 0 0 ~ 1 ~ to
35.500~1m (Figures 6.16 and 6.17). The salinity measurements h m the Eastem
part appear to be closer to the signature of the Southm Ocean water
wtiich has saliniües less than 35.500~100, as reported by Gersbach et al.
(1 999). Consequently, this part of the area of study is more
influenced by cold water m t s . This resutts in lower srrFaœ water
temperatures and salinities, wmpared to Mers f i the Cenûal
GAB. Stations 015 and 016, beheen 40 and 6ûm depth, exhibit
+s8#ul015
1 i-- ul6
-1 000 1 m u n i 6.16 and 6.17 Tempefahm and sdîmity depth profiles at sWbm 007 lo 016. Water h m stations at the e8stemmost part of fhe a m of nssareh edfiiat tamperauies kwer ihan 20.000C and aalinnies bawaari 35.000 '1- and 35.500 O/,. Waten at staqiorrs 015 and 016 have highef safinity due to rnixing procass4s with seawaltr origmati-ng from the C«itai GAB.
salinity values signifcantly highec (35.7oOOlm -35.800Plm) than the surface water
values. The presenœ dthis saline water mas, at this depth, can ôe attributed to
either Central GAB saline surface seawater that extends eastwards or to
evaporated seawater originating h m the Spencer Guif, that flows south. Another
possible reason for the occurrence of the above-mentioned saline water at
stations 015 and 016 wuld be attributed to the vertical mixing of surface saline
water, which evaporates and sinks, with sub-surface, less saline seawater that
upwells to the surface. A comparable phenornenon is observed in the description
of waters collected from station 007, at 40m depth. The saiinity at this depth is
higher, relative to the surface water values. Sirnilarly with stations 01 5 and 016,
flow of saline seawater that extends eastwards or vertical rnixing of waters
(upwelling) wuld have affected the water chemistry at station 007.
As discussed in Section 6.2, surface water temperatures and salinities for
station 054 are lower than those of the evaporated waters in the Gulf (Figures
6.18 and 6.19), due to the infiuence of cold, nuûient n'ch seawater that originates
from the Southern Ocean. The characteristics of the waters collected M m station
054 resemble those of the waters from çoastal stations 041, 039, 023, 022, and
018, which have surface temperatures ranging h m 1460°C to 19.Oû"C and
salinities between 35.400°i00 and 35.600%. This water body, that affects the
abovementioned coastal stations, has resdted from the mixing of GA6 Plume
seawater with waters aiginating h m the Southem Ocean. These waters flow
into the oontinental s W f of the Eastern GAB area and mach shallow depais (les
ttian 200m depth), f m i n g the Fiindm Cumnt water bocfy.
1 Figure 6.18 1 ~ ~ s b o n ~
Fqures 6.18 a d 6.f9 TernpmWe and Hmity depth p d b s at stations 054 to O S . The Spencer Gu# walcn are highîy &me. M e r at station 054 is influenceci by uprvalling and exhibits bww temperahrms and salinities.
Consequently, there is a zone of wann surface water with high salinity that
occurs in the Central GA6 region. This water body is present in caastal waters at
the Head of the Bight as well as in 300km distance Rom the coast. It extends
along the Centrai GA0 coastline and flows eastward, infiuencing the waters in
subsurface depths (4û-60m depth) as east as station 015. This warm, saline
water mass has a similar signature with the GA6 Plume and the Leeuwin Current
because it has a temperature range between 18.00 OC and 20.80 OC, and a
salinity level at 35.800 'lm and 36.160°1~. Further, coastal surface waters (up to
200m depth) are cooler, with lower salinity due to mixing with upwelled waters
that originate from the Southem Ocean. The regional upwelling processes
influence the nutrient contents in the regional coastal waters, as well. Coastal
surface waters have elevated phosphate contents compared to those of surface
waters collected from offshore stations, as presented in Figure 6.20. This
observation indicates that the GAB Plume and the remnant LC water masses,
which are surface, warm, nutrientdepleted water bodies, ocaipy mostly the
surface waters of the outer continental margin of the Eastem GAB, sinœ these
waters feature very low nutrient contents. Beneath these surface water masses,
the cold, low salinity and nutnent rich Flinders Current flows towards the coast,
introducing Southem Ocean originating waters to the region of the Eastern GAB.
Concentration (micromoUL)
Figure 6.26 Phosphate depth profiles in surface waters at coastal stations 007, 010, 022, 039, 051 and 052 (in bold charaders) and at offshore stations 017, 032, 044 and 053. Surf&e waters at coastal stations exhibit higfier nutrient contents than those of surlace waters at offshore stations.
6.5 Eastern GAB General Oceanography - Summary
The following general oceanographical characteristics summarize the
above mentioned observations in the area of research in the Eastern Great
Australian Bight:
Salinity and temperature levels in surface seawater are enhanced in
the Central GAB region due to the influence of a wam, highly saline
water body that has similar charaderistics with the GA0 Plume and
remnant Leeuwin Current waters. As this warrn water mass moves
further Rom the shore, it occupies the surface waters from the coast to
approximately 200km distance from the shore.
Wam, saline waters occur in subsurface waters in the eastem part of
the area of research. This phenomenon may be attributed to water
flowing from the Central GAB eastward or from vertical mking of
waters due to evaporation and upwelling processes.
Cofd, nutrient -rich waters that occur below the 150m depth amss the
area of research, reach the surface in coastal areas, due to upwelling
phenornena. Inaease in nutrient contents is more pronounced in
surface water samples h m the eastem part of the area of research.
This cold current is also detected in subsurface layers along the coast
of Eastern Great Australian Bight Its temperature and salinity levels
resemble the Flinders Current signature.
6.6 Major Elements
The behaviour of the major elements, as determined in this work, is
presented in this sedion. Na, Mg, Ca and S have a generally consenrative profile
in aIl stations of the area of research (Figures 6.21, 6.22, 6.23 and 6.24). These
findings agree with the major element behaviour in various oceanic environments
that has been previously discussed by Bowen et al. (1982), Riley and Chester,
(1 983), Furness and Rainbow (1 990) and Millero (1996).
The average values obtained by the seawater analysis for Na, Mg, Ca
and S are the following: Na 11851+/-4% (RSD); Mg 1451+/-3% (RSD); Ca 491 +/-
5% (MD) ppm and S 1041+/-3.6% (RSD) ppm. These values are slightly higher
than the average values of the major elements in seawater as reported by Riley
and Skirrow (1 975), Riley and Chester (1 983) and Libes (1 992). These reported
values are: Na = 10773 ppm, Mg = 1294 ppm, Ca = 412 ppm and S = 904ppm
(at 3 5 . ~ 3 0 ~ 1 ~ salinity levels). The varienœ in these values is due to the high
salinity levels that occur in the area of research, which exceeds even the
36.000~1~ level at the stations dose to the Head of the Bight Most of the
seawater samptes calledecl in the area of research exhibit a salinity value higher
than 35.000°~00. Only 8 salinity measurements were belw 35.000~im (TIM~ 6.1).
Consequently, the major element concentrations detmined in the seawater
samples colleded in the Eastern Great Australian Bight are slightly enhanced
compared to the major element leveis in Vt reported by previous
researchers (Riley and Slamrw 1975; Riley and Chester 1983 and Libes 1992).
Although Na, Mg, Ca and S profiles show relatkely unifomr concentrations
Concentration (ppm)
l 1 : Na Sbmdad Dmsllan: 310 ppm ' hiaûetdonLini39ppm
Figure 6.21 Na concentrations with depth in seawater samples from al1 stations. The graph shows the enhanceci surface conoentrabions of Na in stations located in the Central GAB. This area is also diaraderfied by high safinity and temperature levels. In waters below 200m deplh, Na vahies appear to diverge from the average value, as a result of mkhg between different waters (GAB surface seawatw with Southern Ocean water).
Concentration (ppm)
staacnsaî7039.w4 (CMfaI GAB)
Figure 6.22 Mg concentrations wiVi depth in seawater sampies fmm d stations. Statiaiis kcated in the Central GAB exhibit higher wiface Mg îhan in other kcabiaris. The variaüons of Mg values in depths gfe!ater than 200m are possibiy due to mmng betweeri diffetent watermasses(GABsurfaceseawatsrniitn~Oceanwater).
A - -
Concentration (ppm) O 100 200 300 100 500 600 700 800
Figure 6.23 Ca concentrations with depth in waters fmm al1 stations. Ca values in surface seawater samples from stations located in Central GA0 are higher than the average Ca amenhüon. In seawater s a m m Imm depths greater aian 200m, aie concentrations vary due to mixing of GAB surface seawater with Southem Ocean deep water.
Concentration (ppm) O 500 lm 1500 2000
Figure 6.24 S concecrtration with depth in seawatw samples from al1 stations. The behaviour of S in the Eastern GAB agrees mth the infomratiort denved fnnn the previousiy presented major eiement pm(iies (Figures 6i, 622,623)-
with depth, there are some deviations from the average value estimated for each
major element across the area of research. Furness and Rainbow (1990), Libes
(1 992) and Millero (1 996) have suggested that a physical factor that can alter the
concentrations of the major elements in seawater is the mixing between water
masses of different salinity. The oceanic environment of Eastern GAB is
influenced by the interaction of two main water bodies with significant diierences
in their salinity levels: The wann, medium-to-tiigh salinity water body, that is
comprised by the GA0 Plume and remnant LC water, and the cold, low-salinity
deep water mass from the Southem Ocean that reaches the surface. As a result,
the small deviations from the mean concentration of each major element reflect
the mixing of these waters wtiich have different salinity and temperature levels
and, therefore, relatively different major element contents. Specifically, surface
seawater samples collected from Central GAB stations (Le. stations 037, 039 and
044) showed higher Na, Mg, Ca and S values than the average values estimated
for each element (Figures 6.21,6.22,6.23 and 6.24). These results indicate that
the intense evaporation phenornena in the Central GAB area caused the
concentration of the major elements in the seawater and, eventually, the
enhancement of their regional surface values. FurVier, al1 four major element
profiles show enhanœd concentrations in the seawater samples fmm stations
032 and 044, at 476m and 544m depth respedively. These waters have low
temperatures (betweeri 80C and 9%) and very low salinities (beheen 34.600~1~
and 34.80001~). Consequerrtly. the occurrence of a cold water mass with low
salinity but high major element contents at these depths is possibly due to
vertical mixing of waters. This water was originally on the surface where it was
subjected to intense evaporation which, in tum, led to increased major element
concentrations. The sinking of this water rnass to deeper layers of the water
column caused a decrease in its initial temperature and salinity levels.
Additionally, the low major element contents rneasured in seawater samples from
depths greater than 600m indicate the presence of the cold, Southem Oœan
originating water mass that flows in the Eastern GA6 region.
6.7 Consewative Elements
The results for the conservative elements of interest, that were analyzed in
this work, prove that Mo, U, Cs and Rb have unifon concentrations with depth in
the area of study. Figures 6.25, &26,6.27 and 6.28 present the results obtained
for ail stations in the Eastem GAB. As shown in these graphs, Mo, U, Cs and Rb
behave consewatively along the water column, in al1 water masses examined in
the area of study (i.e. GAB Plume - remnant Leeuwin Curent waters at the
surface and Southem Ocean originating intermediate-deep water).
The average concentrations for the consetvative elements of interest were
determined in this study as: Mo 10.10 +/- 0.9% (RSD) ppb, U 3.32 +/- 8%(RSD)
ppb, Cs 0.1 80 +/- 27% (RSD) ppb and Rb 109 +1- 10% (RSD) ppb, at 35.400 '/a
salinity average. The conservative elernents published values in open ocean
waters, as repartecl by Riley and Chester (1983). Fumess and Rainbow (1990)
and M i l h (1996). are: Mo 10.7ppb. U 3.2ppb, Cs O.2ppb and Rb 119ppb, at 35
Of, -y, the conseruative demerit caricentrations obtained analytically
in the a m n t study for the Eastern GAB region are comparable with previously
Mo concentration (ppb)
O 2 4 6 8 10 12 14
Mo Standard Oéviaüon: 0.08 ppb ' Mo üeîsction timits: 0.03 ppb
Figum 6.25 and 626 VertNal d i i n s of Mo and U- These &merils behaie conservalnely in the GAB ma- envimnment, as they have unifwm corieenlrations wïth depth. Denations f m the average values are due to water mmng pmesses in intennedîae waters. Mo values in seawater samples from Station 016, at 5Irndepîh menhanoed. po&b@dueto kcdsma'œs-
Cs concentration (ppb)
L
: Cs Standard Deviation: 0.009 ppb I Cs Detecüon ümik 0.002 ppb I I
Rb concentration (ppb)
O 50 1 O0 150 200
Figures 6.27 and 628 Vertical dibutions of Cs and Rb. lkse ekmenÉs betme . * - in the
GAB mananne environment, as they have uniFomi m n s with depth. Dewaûom fr#n aie average values are due to water mMng pmcesses in intermedate waters. Cs values in sawater sa* h n Station 016, at 51m depth. are erihanœd, possbly due to kcal saross.
published values in ocean waters. However, the Mo, U, Cs and Rb profiles
feature the same characteristic with the vertical distributions of the major
elements Na, Mg, Ca and S, with tespect to ml1 deviations from the average
elemental value (Section 6.6). Fumess and Rainbow (1990) suggest that mixing
between waters of different marine chemistry may result in the obsewed
variations for the conservative element concentrations. As a result, the small
deviations obsewed in the vertical disîributions of Mo, U, Cs and Rb may reflect
the interaction of different water bodies in the area of the Eastem GAB.
The consewative behaviour of Mo and U has been investigated in various
oceanic regions. For example, Van der Weijden et al. (1 990) have presented Mo
and U profiles in Eastern Mediterranean Sea Mo and U distributions exhibited
Iittle variation with depth and location in their study. The average concentrations
of these elements in the Eastern Mediterranean Sea were 13.4 ppb and 3.4ppb,
respedively.
Cs and Rb have been desdbed as asmat i ve by Bowen et al. (1982),
Riley and Chester (1983) and Fumess and Rainbow (1990). The behaviour of
these two elernents in the Eastern GA6 marine environment agrees with
previous investigations in North Atlantic and Pacific Ocean (Bowen et al., 1982).
Folsom (1984) reporteci a relationship between Cs concentrations and
salinity variations in North Pacifie- According to Bis author, Cs values decreased
in deep waters with lawer salinity than îhe surface waters. Cs profile in the
Eastem GAB rnkoment appeas alsa ta be influenced by salinity changes.
Li belongs to the mservative elements group, as stated in Section 3.3.2.
Its profile is presented in Appendi I (Figure 1.1) Li analysis in the curent
investigation was challenged by various factors, as discussed in Section 5.5.
Therefore, Li behaviour in the area of research was not possible to detemine.
6.8 Genenl Recycled Metal Distributions
Ba profile shows generally a surface depletion which is followed by an
increase in concentration with depth. The average concentration for Ba in surface
(0-200m) and intemiediate waters (200-991m) in the area of study were
determined as 4.77 +/- 1.7% (RSD) and 5.01 +1- 1.7% (RSD) respectively.
Figure 6.31 presents the Ba profile for al1 stations in the area of research. The
elemental distribution demonstrated on this graph agrees the profiles presented
for this element by Broecker and Peng (1982), Riley and Chester (1983) and
Millero (1996).
The distribution of Ba resembles the profiles of the nutrients, as presented
in Figures (figures 6.5, 6.6, and 6.7), e ~ p ~ a l l y to silica. The variations in the
Ba concentrations in the water column indicates that the distinct water masses
that flow in the area of the Eastern GAB have an effect on the Ba levels, similar
to that of nutrient contents. For example, the cold, nutrient-ridi waters that flow in
depths greater than 600m show a pronounced increase in Ba concentrations
relatively to shallower waters (Figure 6.29). Addiionally, Ba values measured in
seawater frwn the #lastal staücms 016,022 and 039 were high. These
stations are located in amas whem #rasta1 upwelling ocarrs, as diswssed
previasiyviawfy The nuEnent wntents in the seawater samples from these stations
Ba concentration (ppb)
' * Station 039
1 Station 022 Station
i
l
Ba Standard Deviatian: 0.09 ppb Ba Dateclion tirnitr: 0.04 ppb
Fiiun 6.29 Recyded metal vertical distnbuoions: Ba profile in the GAB mafine environment shows a proriounad surface dcpktion, fdlowed by an increase in conammion witn deptn due to the uiuusion d nutrierit- waters fmm the Southem Ocsan. Surface waters at aasW $Wons 051 and 052 exhibit high Ba M n t P n t A
m e similarly enhanced. ConsequenUy, the mixing between waters with
diierent nutriutrient concentrations is refiected in the Ba behaviour in the Eastern
GAB. From the data obtained, it is evident that high Ba levels are indicative of the
presence of the Southern Ocean originating, nutrient-rich water mass. Also,
according to James et al. (2001), the upwelling of nutrient-rich waters near the
shore results in bryozoann'ch sediments and active carbonate production.
Figures 6.30 and 6.31 present the vertical distributions for two other
recycled elements of interest: V and Cr. Their average concentrations in surface
(0-200m) and intermediate waters (200-991m) in the area of study are presented
in Table 5.5. The analytical precision for these elements was 14% (RSD) and
16% (RSD), whereas Ba analytical precision was 1.7% (RSD). Therefore, the V
and Cr profiles for al1 stations in the above-mentioned Figures cannot provide a
clear description of the elemental behaviour in the GAB marine environment.
Generally, V shows uniforrn concentrations with depth (Figure 6.30). Riley
and Chester (1983) reported a similar, nodepth pattern V profile for the North-
eastern Atlantic for a number of staüons to a depth of 1OOOm - comparable depth
with the curent investigation, where the deepest seawater sample was collected
frorn 991 m depth. Middelburg et al. (1988) have also reported small variations in
V concentrations in North Atlantic Ocean, with no indication of pronounced
surface depletion.
Cr concentrations show a slight decrease in surface layers relatively
to deeper waters, as demonstrated in Figure 6.31. However, for rnost stations,
Cr demonstrates a relatively uniforrn concentration with depth Cr has been
V concentration (ppb) O 0.5 1 1 .S 2 2.5 3
V Standard Devialion: 0.16 ppb V Deledian Limits: 0.03 pp4
Cr concentration (ppb)
0.1 0.2 0.3 0.4 0.5 0.6
Figures 6.30 and 6.31 V concentfations (Figun 6 3 ) and Cr conœntmüons with depth (FÎÎun 6.31). V and Cr behaviour in the Eastern GA8 water cdumn hss no d e p t h h M patkm- Cr #nranbatiori in sampk Swm077291appears enlmœd,duabawdsmnabon
. - m. - -
reported in the literature as a nutrient-iike element with small surface depletion
and constant level at depth (Riley and Chester, 1983). Consequently, the
information derived frcm the Cr distributions in this research agrees with previous
publications.
Cd, Cu, Ni and Zn vertical profiles for al1 stations are induded in Appendix
II, Their average concentrations in surface (0-200m) and intemediate waters
(200-991m) in the area of study are presented in TaMe 5.5. These nutrient-like
elements were analyzed with low precision (as discussed in Section 5.5) and
their distributions are not clear. Further researdi could be coriducted for better
determination of the Cd, Cu, Ni and Zn behaviour in the GAB marine
environment.
6.9 Correlation between Nutrients and Recyded metals
The variations in Ba concentrations with depth are similar to those of nitrate,
silica and phosphate contents in seawater samples from inshore and offshre
stations of FR 03/98 mise. Ba is one of the nutnent-like elements of interest that
showed good analytical precision in this study (1.7%). Thetefore, its profile can
be used as indicator of the distributions of the remaining recycied elements that
are induded in this study. The distributions of Ba concentrations in each station
of the FR 03/98 mise are inciuded in Section 6.1 1.
There is a positive correlation between nutrient concentrations and Ba
values in s m k e waters at stations kxated at the eastemmost part of the area of
research (Figures 6.32, 6.33 and 6.34). H i e , phosphate and silica levels
appear enharmd in surface coastai waters compared to surface seawater ftom
I
3 ' O 1 2 3 4 5 a - --
F Qum8 6.32 ta 6.34 Conelation betuiieen nubient contents anâ Ba awiesntrations in waters at stations 010 and 015- These stations are locaied on the same &h-nshon tmsect (Fgun 6-1).
offshore station O1 5. This proves that nutnent-rich water reaches the coast and
flows upward to the surface seawater layers, as indicated by the nutrient
information in seawater sample from the coastal station 010, at 44m depth.
Similady, the nutrient-rich water mass influences the recycled metal
concentrations in samples from the same stations (stations 015 and 010). Ba
levels are increased in surface seawater at station 010 compared to Ba surface
seawater levels from station 01 5,
A good agreement between nitrate, phosphate, silica levels and Ba
concentrations occurs in surface seawater samples at stations 017 to 025.
Figures 6.35, 6.36 and 6.37). It is evident that nutrient concentrations are
elevated in stations doser to the coast. For example, nutrient concentraüons in
seawater from coastal station 022, (at 70m depth) are higher by a factor of 5
compared to station 017 (at 101 rn depth) which is Iocated at a distance of 150km
from the coast. Similarly, Ba concentfation increases in seawater samples fmm
nearshore stations. Therefore, the upwelled coastal waters that fiow in the area
of study dunng the time of the FR0398 mise (March-April 1998) are
charaderized by high recycled metal contents oompared to those of the offshore
surface waters which have l m nutrient and recyded metal levels.
Comparable observations can be made for surface waters that were
collecteci from offshore and inshore stations Iocated in the Central GAB area,
namely stations 032 to 039 (Figures 6.38, 6.39 and 6.40) and -ans 044 to
O51 (Figures 6.41, 6.42 and 6.43). Nutrients and Ba levels demmate a
positive correlation in surface waters at inshore and onshore between
c. - - T 2 3 1 5 6 7 SQei(niciiPi#lll)
Figures 6.38 to 6.40 Cordation between nutrient contents and Ba coneeritrations in waters at stations 032 to 039. fhese -ans are bcated m the same ~ - n s h o r e trarrsed (F~ure 6-1)-
- -
1 Figure 6.41 1
0 !
O 1 2 3 4 5 6 - 1
- ( m l Figures 6.41 to 6.43 Correlation between nutrient contents and Ba coriœntrations in waters at stations 044 to 051. These stations are located an the same oflShoreinshore transed (Figure 6.1). - *
stations 032 and 039. Recycied metal values are increased for seawater samples
collected from nearshore stations. Similady, nutnent leveis appear to follow the
sarne trend. Consequently, the nutrient rich Flinders Curent water appears in
surface waters close to the Central GAB coast, features enhanced recycfed
metal levels and can be traced in waters as shallow as at 24m depth (station
039, 24m depth). Surface waters at the offshore station 032 are afFected by the
GA0 Plume water mass and, as a result, have fow nutrient and recycled metal
content. Coastal surface waters at stations located at the Head of the Bight have
higher nutrient and Ba concentrations campared to Viose of the offshore stations
(Figures 6.41, 6.42 and 6.43). This indicates that the surface waters at the
offshore station 044 are mainty affecteci by the presenœ of the wam, nutrient-
depleted GA0 Plume wtiereas the coasbl waters are infiuenced by the mixing of
the underlying nutrient rich Flinders Cument water mass with the GA6 Plume.
As a result, the above-mentioned graphs illustrate a positive correlation
between recycled metal distributions and nutrient levels. Nearshore stations
exhibit higher recyded metal and r#ltr*ent values than stations further from the
coast (400km). Consequently, the underiining cold, nutrient-rich water mass of
the Flinders Curent moves onto the continental shelf, reaching surface waters
and infiuencing surface water Ba content and nutrient Ievels.
6.10 General Scavenged Metal Distributions
Generally, Mn concentrations show a slight decrease with depth in most
Eastern GAB stations (Figure 6.44). The average concentration for Mn in surface
(0-200m) and intermediate waters (200-991m) in the area of study were
detennined as 0.195 +/- 6.5% and 0.214 +1- 6.5% respectively. Saager et al.
(1 993) have also shown elevated Mn concentrations in eastem Mediterranean
Sea surface waters that decrease due to particle scavenging until the lOOOm
depth. Millero (1996) has reported that dissoived Mn is nomally enriched in
surface waters relative to the rest of the water column. However, the change in
the oxidation state, that Mn undergoes in oxygen-rich seawater, affects its
geochemical mobility and, consequently, its concentration in seawater (Fumess
and Rainbow, 1990; Millero, 1996). Eastern GAB is an area of vertical mixing, as
indicated previously by the major elernent profiles and the behaviour of Ba. The
regional upwelling of cold, dense waters influences the oxygen content in the
water calumn because the Southem Ocean deep waters are high in oxygen
content (Bruland, 1983; Millero, 1992). Therefore, Mn (+2) oxidizes to Mn (+4)
which is the least soluble species of this element. This phenornenon may help
explain the low concentrations of Mn (dose to the detedion limits of the method
used).
Co and Fe vertical distributions are presented in Figures 6.45 and 6.46.
Their average coricentrations in surface (0-2ûûn) and intemiediate waters (200-
991 m) in the area of study are pmsmted in Tabk S.S. As discussed in Section
5.2, the analytical resuits br these two elements uiwe challenged by various
Mn concentration (ppb)
Mn Standard Dewiaüon: 0.178 ppb Mn Detedion Limits: 0.029 ppb
Figum 6.44 Scaveriged metd dirstniutions: Mn exhibits enhanced concentrations in surface waters of the area of msearch. In d q r waters, Mn ieveis decrease due to the sce~nging charader of ihe elment Bekw 5OOm de@, Mn concenbations wre bdaw detediori Iimit,
Co concentmtion (ppb)
Co Standard Deviation: 0.022 ppb Co Detection Limits: 0,010 ppb
Fe concentration (ppb)
O 2 4 6 8 10
Fe Standard Deviation: 0.590 ppb Co Detection Limits: 0.094 ppb
parameters. As a result, the information derived fmm their profiles shauld be
looked upon with caution. 60th elements demonstrate a small depletion with
depth. Bwen et al. (1982) and Fumess and Rainbow (1990) indicate the
scavenging character of these two elements.
Pb and Al profiles are presented in Appendix III. Their average
concentrations in surface (0-200m) and intemediate waters (200-991 m) in the
area of study are presented in Table 5.5. The analytical results for these two
elements demonstrated poor precision. Therefore, it is not possible to detemine
with any accuracy their behaviour within the GA0 marine environment.
6.f 1 Description of All Stations 007457 - Correlation with
Recycled and Scavenging metals
This section discusses the oceanographical characteristics of stations
007-057 in the area of research. A general description of the main water masses
and their circulation in the Eastern GAB area is presented in Figure 6.47. The
distributions of two trace elements of interest (Ba and Mn) are presented for each
station in order to examine the influence of the oceanography of the region on
the elemental concentrations. These two elements belong in diffwent groups: Ba
is a recyded element and Mn is a scavenging elernent Ba and Mn democistrated
very good analytical -sion in the current study with 1.7% (RSD) and 6S%
(RSD) respedively. Consequentiy, their profiles can provide reliable information
on the behaviour of the recycled metals and the scavenged metals in GAB
manne environment
6.1 i .l Stations OOf 425
Temperature and salinity infwnation fiom station 007 shows that the
surFaœ water (3.7m depth) has high temperature (17.50 O C ) and low salinity at
35.160~1~. At 40.3m depth. the salinity inaeases whereas the temperature
starts ta drop. Deeper water layers (135Sm to 291m) have c a l temperature
(1 1.00-12.00°C), sa6n1ty levels sirnijar or lower than the surface waters and high
concentrations of nutrients (Figure 6.47).
The profile of station 007 regarding temperature, salinity variations and
nutrient levds. is charaderistic of other stations within this locaiii in the area of
research. The high temperature of the surface water is due ta dimatic
parameters. Since the mise took place in the austral fall, the aîr temperatures
were still high (Section 2.2.7). Miing phenomena have possibty caused the
sinking of sur$ce water (mth saünity of 3~.323~im) to 40.3m depth and the
upwelling of oceanic water with loww salinity (35.160 O/@) to the surface. The
deeper water masses (hm 135m to 291 m d m ) have law temperature (around
12 OC) and low saiinity (35.100 to 35.~)0~100), indicating the presence of water
originating from the m e m Ocean Cunent System. Therefore, the nutrient
levek at these depths are much higher than the surface waters (Figures 6 4 ,
6.49 and 6.50).
Station 009 edibits the same charaderistics as -on 007 with respect
to the su- (3.3m) and deeper waters (265.5m). ats described above.
However, no data is a v a i i fix the intermed'iate layes of mis M o n as no
datawasalkctdatthesedepths
3 6 O -.. .
Australian
Figure 6.47 (a) Map of the FR 03 1 98 crulse in the Eastern Great Australian Bight (Transects A, B, C & D)
Figures 6.18 to 6.50 Nutrient concentrations with depth in waters from stations 007 to 016. Phosphate, Nitrate and Silica levels increase with de@. W m at #iastal station 010 show enhanceci nutrient cmtenîs at shallow depths, due to ugwelling. - --
Proceeding northwestwards, station 010 surfa08 water also has high
temperature and intermediate salinity. However. the phenomenon of upwelling
here seems more intense because at depth as shallow as 40m, the temperature
drops at 13-60 O C and the salinity also decreases (Figure 6.47). At this depth,
nutrient levels have already reached a significant concentration (Figures 6.48,
6.49 and 6.50).
Samples at stations 015 and 016 show a similar pattern with station 007,
with respect to temperature and salinity distributions. The presence of warm, high
salinity (-35.800 ' lm) water is observeci, at 60m and 50m depth for stations 015
and 016 respectively (Figure 6.41). due to mixing with saline water that
originates from the Central GAB or the Spencer Gulf. Shallower waters in both
stations have lower salinity. The origin of this wam water mass was previously
discussed, as well, in Section 6.2.
Station 015 exhibits a surface salinity value of 3 2 3 8 0 ~ 1 ~ at 5m depth
(faMe 6.1). This surface, low salinity water mass could possibly be attn'buted to
a local fresh water source, namely the Mumy River, which is the only river in the
area. It has an average annual disdrarge of only 0.89 m3 per semnd, and. in
places, has dried up on at least three occasions (Longhurst, 1998). Furthemore,
its delta is located in a long distance (3ûûkm approximately) from station Of S.
Thereftm, the water discharge fium this river does not affed the rqional manne
chemistry. As well, the fdlowing graphs (Figures 6.51 md 6.52) do not show
any signficant iwease of trace metais ammb'ations in çeawatef samples from
Mn Concentration (ppb)
O 1 2 3 4
Figurus 6.51 to 6.52 Ba and Mn contents with d m in waters at stations 007 to 016. Ba shows a sligM inmase with depai. Mn elevated ~mmtratïons in waters at station ûû7 (291 rn depai) are due to metal release frwn sheif sediments-
station 015, at 5m depth. This is the only station in the entire area of research
that had such low surface salinity.
Ba appears to have uniforni concentrations with depth in seawater
samples from station 007 (Figure 6.51). Although the nutrient levels increase
significantly below 65m depth ,Ba levels remain relatively the same. However, Ba
shows a slight depletion near the surface in waters colteded from station 016.
Scavenged metals distributions in the area enwmpassing stations 007 to
016 are represented by the prafiles of Mn (Figure 6.52)- As reported in Section
3.3.4, the scavenged metals are expeded to show a decrease in concentration
with depth. Due to mixing of waters in this area, however, Mn contents appear to
reach a middepth maxima at -300m depth. This increase in concentration is due
to metal release from the shelf sediments because the water sarnple cdlected at
291 m was close to the bottom of the water wlumn (Figure 6.1 and Figure 6.47).
The next stations of the mise were 017 to 023 (Figure 6.1). Station 017
is further from the coast. The temperature and salinity data from this station show
a gradua1 decrease with depth. Station 018, at 204m depth, has comparable
information with station 017 at similar depth (198111). The nutrientnch, cold
Flinders Current can be traced at these depths (Figure 6.47).
Station 022 exhibits high surface temperatures (A8.48'C) and salinity at
35.678 O h . . Information for both stations 022 and 023, from intermediate depths,
shows a decrease in temperature and salinity and an increase in nment levels
(Figurrw 6.48, 6.49 and 6.a). Interesüngly, the nutnents concerrtratioris
reported for station 022, at 7Om depth, are higher than the -ents ievel at
deeper waters at station 018. This obmaüon irnplies ttiat coastal stations 02.2
and 023 are more infiuenœd by upwelling than station 01 8.
Proceeding westwards in the area of çtudy, next is station 025.
Information fmm this station shows that the temperature and salinity gradually
decrease with depth and there is no evidence of upwelling in the surface and
intermediate water layers. At a depth of 439m, the lm-salinity, cold and nutrient-
flch gyral cuvent (i.e. Flinders Current) a n be traced. At the surface (3.7m
depth), Vie temperature reaches 20.33OC and the salinity level is at 35.839 Oloo.
This high-temperature, high-saiinity water signature is simiiar to the surface
waters at station 017 (Figure 6.47). This indicates the presence of the GA6
Plume in the area, as it moves eastwards, during the austral fa11 (Sections
2.2.6.1 and 2.2.7).
Ba distribution for these stations is presented in Figure 6.53. This graph
shows that Ba concentrations are relatively constant with depth 4 t h a slight
depletion at the surface water- for station 017. However, data for station 022
show mat Ba surface concentrations are higher than for station 018 at the same
depth. Consequently, the coastal upwelling is chamcterized by enhanced metal
values. Ba distributions for the -on 025 are presented in Figure 6.53.
Comparing the Ba concentrations in surface (3.7m depth) and deep water (439rn
depth) samples, it is obvious mat Ba exhbits a surface depletion- As depth and
nutn-ent levels increase, Ba increases as well.
Mn profiles for the above-mentioned stations are presented in Figure
6.54- Surfaœ water concentrations in station 022 are lower wrnpared to Mn
contents in station 025 where a slight deerease with depth ocairs. This indiCates
Mn COIICllltnUon (ppb) O 1 2 3 4
the influence of the oxygen rich Flinders Cuvent that flows in the area of study,
occupying the intermediate depth layers.
6.1 1.2 Stations 032453
GAB Plume is traced at the surface of station 032, where the water has
temperatures as high as 20.87'C and salinity of 36.1 32Olo0 (F igun 6.47). High
salinity waters (35.938 'la) accun even at 124m depth, although the
temperature decreases significantly and the nutrient levels rises (Figures 6.55,
6.56 and 6.57). This is possibly due to mixing of the Plume with waters
originating from the Flinders Current.
Surface seawater at station 037 exhibits warm temperatures (at 19.79 OC)
and relative1 y low salinity (at 35.79$100). These water characteristics continue ta
appear at intermediate depth (75.8rn), with a decrease in temperature, due to
mixing with colder waters. Low salinity (35.541-35.632~1m) shallow waters
combined with warm surfaœ temperatures at the stations 039 and 041 indicate
the existence of upwelling and mixing phenornena near the coast (Figure 6.47).
Ba distributions for the above-mentioned stations are presented in Figure
6.58. This Ba profile shows a sligM depletion at the surface waters but the
concentration remains relatively constant 476m depth. Mn behaviwr at the
stations d e m i above shows a scavenging character, as the elemental
comentration reduces with depth (Figure 8.59).
The next transed of the eruise line indudes statioris 044 to 052 (Figure
6.1)- The surface waters uf these exhibit very high temperatures (20.75
to 20-91 OC) and salinities hïgher than & I ~ ~ These water charaderistics indicate
1 Figure 6.55 1
1 Figure 6.58 1
Mn Concentration (ppb) O I 2 3 4
Figum 6.58 to 6.59 Ba and Mn contents with depth in waters frwn stations 032 to 039. Ba increase with depth, fMlowing the nutrient trends. In coastal stations (039) Ba mtents are ehted. Mn ooncentrations decrease witfi depth, due to oxidation that affeds the solubilï of the element
the presence of the GA6 Plume in the area. Lower temperatures and salinities in
surface waters collected from stations doser to the coast imply the influence of
the LeeuWin Current water body that is introduced in the region of study during
the FR03198 mise in March-Aprili998 (Figure 6.47).
.Ba distributions for these stations are presented in Figure 6.60. At station
049, Ba shows a nutrient-like charader, as it increases with depth. The same
pattern is depicted in samples from station 044. Stations 052 and 051, which are
close to the coast, gave very high Ba concentrations at intemediate depth. It is
questioned, though, whether these values refiect local sources or contamination
during laboratory sample treatment. Mn profiles for these stations are presented
in Figure 6.61. Although the available data are not sufkient to describe cleariy
the distribution of this element, Mn values for station 044 show a decrease with
depth.
Station 053 is the only station in the available data set from cmise FR
03/98 that a depth of 991m is reached (Figure 6.47). At this depth, the nutrient
concentrations are very high, where as the temperature and the salinity levels
are significantly low (3.95OC and 34.437Plm). This water mass has its source in
the Southern Ocean system. At the surface of station 053 (at 5m depth), the
influence of the GAB Plume is tracecl, as it is indicated by the high temperature
and salinity of the waters (20.53 OC and 36.002@100, re~pe~vely).
The behaviour of Ba at 053 is presented in Figwe 6.62. In this
graph, Ba has definitely a nuûîent-iike charaaer. as the concentrations increase
Mn Concentration (ppb) O 0.5 1 1.5 2 2.5 3 3.5 4
Figures 6.60 to 6.61 Ba and Mn contents with depth in waters fm stations 044 to 049. Ba kvek increase with deph, infiuenced by n-nt rich waters that Ikw in the Eastern GA6 at intemred'ie depths- Mn kveîs
- -7
1 Figure 6.63 1 Fium 6.62 to 6.63 Ba and Mn contents with de@h in waters h m stations 050 to 053. Ba ievels increase with depth, influenced by nutrient rich waters that originate from the Ssouthem Ocean. Mn bels decrease, afïècted by o ~ p r o e e s s e s -
with depth. Figure 6.63 shows the Mn distribution for station 053. The available
data, wtiich do not exceed the 2Wm depth, indicate Mat the Mn conceritrations
remain relativety constant until this depth.
6.1 1.3 Stations 054457
Four stations in the Spencer Gulf were inciudd in the FR03198 mise
(Figure 6.1). Information on station 054 shows that the surface waters have high
temperatures (19.02 O C ) combined with low salinities (at 35.662 'lm). These
waters are underlined by d d , low-salinity water layers (Figure 6.47).
Consequently, station 054 is infiuenced by the upwelling that occurs in this part
of the area of the GAB.
Water masses at stations 055, 056 and 057, though, experience very high
temperatures and salinities (19.84OC - 2O.5l0C and 36.797O/m to 37.178Olm
respectively). These water masses are sumunded by land (Figure 6.1). As
discussed in Section 6.2, the surface water temperature at these stations is
infiuenced primarily by the coastal dimatic conditions, which are charaderized by
warm air temperatures. The elevated suface salinity values possibly result h m
excessive evapmtion. Nutrient concentrations in waters at the Spencer Gulf are
low, with the exception of the seawater at station 054, which shaws an increase
in nutrient Ievels with depth (Figureû 6.64,6.65 and 6.66)
Recycled rnetai information for these stations (Figure 6.67) shows a slight
surface depletion in station 054. HOW~VQT, scawnged metal information (Figure
6.68) for these stations is not sufficient to illustrate dear distributions.
1 Figure 6.64 1
1 Figure 6.66 1
-1000 - Rgum 6.64 to 6.66 NWent contents with depth in waters from the Spencer Guü. These watersmverybwin n idr ier i tsmintheexee9oor idthe~ni lnr fedat~054, wh i i is bcated outside of the Guîf and is intkienced - - by ipweling-
Mn Concontration (ppb)
Figure 6.67 to 6.68 Ba and Mn CO(ICeRtrBtions with depth in waters from -ans 054 to 057. The elenieritaI profles show no depth related pattern in the S~ericer Gulf waters.
PART 2
6.12 Cornparison of the Eastern GAB with the
Mediterranean Sea and the N.Atlantic Ocean.
6.12.1 Oceanic and Mediterranean Sea Residence Times
Mediterranean Sea is a deep-water formation area with intense vertical
mixing (Boyle et al., 1985). The dynamics of the vertical water circulation in this
region affects the residence times of the seawater constituents. Compared to an
oceanic environment such as the North Atfantic Oœan, the Mediterranean Sea
trace elements residence times are much shorter (Boyle et al., 1985; Saager et
al., 1993). Laumond et a[. (1984) have conciuded that Pb residence time in the
western basin of the Mediterranean Sea is only 15 yeaw, and in the eastem
basin is estimated to be 60 yeaw. These estimations are very short compared to
the 100 years oceanic residence time that it is reported for Pb in Section 3.3.1.
Measures and Edmond (1988) report that the Al residenœ time in Western
Mediterranean Deep Water may be in the order of 30 years. Compared to the Al
oceanic residence time, which is 620 years (Table 3.1), the above-mentioned
estimation is short. As well, Tankere and Statham (1996) have reported that Cd
residenœ time in the Adriatic basin of the Meditenanean Sea in only 4 years, As
stated in the Iiterature review (TaMe 3.1), though, the oceanic residence time for
Cd is estimated to be 104 years (Wong et al., 1981). Consequently, the
hydrological characteristics of the Meditenanean Sea influences the trace
element chernical kinetics in the region.
The Great Australian Bight marine environment is characterized by vertical
mixing in surface and intermediate waters, as show previously. Therefore, the
elemental behaviour in the GAB environment could resemble the Mediterranean
Sea water chemistry, with respect to trace element residence times. However,
the Great Australian Bight deep water originates from the west wind drift of the
Southem Ocean current system (Section 22.6.4). As discussed previwsly, this
gyral current intnides the GA0 marine environment and infiuences the chernical
kinetics of the regional marine environment. As a result, GA6 elemental deep
water residence times are expected to be closer to oceanic residence times.
6.1 2.2 Temperature Profiles in the three Regions
Table 6.2 presents temperature information for Northwest Atlantic,
Western Mediterranean Sea and Eastern GA0 from surface waters to 1000m
depth. The temperature data set for Northwest Atlantic were published by Yeats
and Campbell (1983). The Western Mediterranean Sea data set is from the
hydrological data reported by Bafiï et al. (1997). Temperature infomation for
Eastem GAB region describe the seawater collected at station Q53 (Figure 6.1).
The infamation from this station was seleded because it provides information for
al1 water layers, between 0-1000m depth approximately.
Table 6.2 Tempetahite and depth infomiatim from Norlhwestem Atlantic, Western Mediterranean and Eastem Great Australian W i t t The data sets for aie first two regions were published by Yeats and Campbell (1983) and Baifi et al. (1997), respectively. The Eastern GA6 data is taken from station 053.
Eastern GA6
The Eastern GA0 surface waters have higher temperature levels than the
other two regions (Figure 6.69). Until the 2Wm depth, the temperature profile in
the region of study is comparable to the Mediimnean Sea one. This
observation can result from the similar ciimatic characteristics between the two
areas, such as the high evaporation processes that ~ x u r in both regions (also
diswssed in Sections 2.4.4 and 2.27). The Mediterranean environment is
characterized by low precipitation, hi* temperature and enhanced salinity Ievels.
The Eastem GAB region has similar dimatic charaderistics and is influenced by
wam, saline surface currents (Le. the GAB Plume and the Leeuwin Curent).
However, below the 400m depth, the GAB water temperature decreases and
resembles to the North Atlantic Vitemiediate water temgerature, which ranges
between 3 O C and 5 OC. This is due to ttie intrusintrusion of col4 water from the
Southem Oœan in the Eastem GAB.
6.12.3 Salinity Profiles in the three Regions
Table 6.3 shows the salinity profiles of the same published data sets that
were used in the previous section.
Table 6.3 Salinity and depth information from Noraiwestern Atlantic, Western Mediterranean and Eastern Great Australian BiiM The data sets for the two former regions were published by Yeats and Campbell (1983) and Baffi et al. (1997), respeaively. Eastern GAB data describe the station 053.
Norüiwestern Western Atlantic Ocean I Eastern GAB
Depth (rn) Salinity cl,) Salinity ("1, ) Depth (m) Salinity cf, 12 34.9 36.7 5 36.002
47 34.9 37.1 100 35.418
191 34.78 37.8 190 35.505
495 34.9 38.05 - *
682 34.89 38 699 34.51 1
908 34.88 37.9 991 34.437
The salinity profile of the Eastern GA0 is doser to the N. Atlantic one. At
the surface, the Eastern GA0 salinity levels are higher than the N. Atlantic
oceanic surface salinity but they are l m r than the Meditenanean surface
salinity (Figum 6.70). This observation can be attributed to the fact that the
Eastern GAB hydrology is charaderized by vertical mwng behiveen wann, saline
surface water and cold, deep water from the Southem Ocean. Therefore, the
Eastem GAB salinity profile combines the characteristics of a m, highly
evaporated Mediianean-type water mass at the surface with an m i c . lm-
salinity water in greater depüt.
In deeper water masses, the Eastern GAB salinity drops even lower than
the North Atlantic levels. This may be a result of the influence that the
Mediterranean Outfiow has on the salinity distribution in the Northwestern
Atlantic. The Mediterranean Outfiow is a dense, high salinity water mass that
mixes with the North Atlantic Deep Water and causes an increase in salinity at
ca.100m depth (previously discussed in Section 2.5.4.2 As a result, the
salinities in this area of the Atlantic Ocean may appear higher than in other
oceanic regions.
6.12.4 Nutrients Profiles in the three Regions
Table 6.4 present the distributions of phosphate, nitrate and silicate in the
three regions discussed above. The same data set was used for the Northwest
Atlantic region and the Eastem GAB, as mentioned in Section 6.12.3. However,
the nutrient profiles for Eastem Meditmanean Sea, that are utilized hem, were
published previously by Boyle et al. (1985).
The nutrient distributions p m t e d in Figures 6.71, 6.72 and 6.73 show
that the surface waters in the Eastem GA8 have a nutrient depleted character
and resemble the Mediterranean surface water profile. However, below the 200m
depth, the Eastem GA6 waters exhibit higher phosphate, nitrate and silica
ammbaüons. These concentrations are comparable to the N. Atlantic values.
The high nutrient levels in the Eastern GAB intermediate and deep waters is due
ta the presence of the Flinders Curent and the upwelling processes mat ocair in
the region (Section 22.7).
Table 6.4 Nutrients and depth information from Northwestem Atlantic, Western Mediterranean and Eastern Great Australian Bight. The data sets for the two former regions were published by Yeats and Campbell (1983) and Boyle et al. (1 985), respedively. Eastern GAB data describe the station 053.
Northwesfern Atlantic Eastern GA8
Dspth Phosphate N i i e S l h bepth Phosphate N i e Silica
(m) 1 @nlOK) I I Ouno#) QunoK) (m) (Iim~tfL) 1 1 ()unoVL) ()unaVL)
6.1 2.5 Trace Metals Levels in the t h m Regions
figures 6.74, 6.75, 8.76, and 6.n present m e of the elements of
interest in the üme regions, at surface (0-200m depth) and at deeper water
layers (200-1000m depth), Mn, Cu, Ni, Cd and Cr are the rrost well doarmented
in previous publications abwt Meaderronean Saa and North Aüanüc Ocean
Figun 6.71.6.72, and 6.73 Nutnwit 4b the Norannihst Atlantic Oosan, ths Wmtm WLmnean Sem and the B s k m GAB mgion. Nubient kvels in the GA6 su- seawater sesmbbeawnparabkwiü i thenmmmtnsw-ofa ie -n Ssa, In dmper GA0 waters, nitrabs, silica and pb6pbb ooricsntrations am snhanesd, ~ r s d t o t h e h n i o ~ ~ . . . .
O 0.2 0.4 0.6 0.8 1 1.2 1 -4
N. Atlantic values (ppb)
N. Atiantic values (ppb)
muni 6.74 and 6-76 ùeîwen Eastern GA0 and Norütwest Atlantic trace skrrisrits ieveh in su- (&2Wm - Figure 6.74) and dmp Wers (201F10aQm - Figura 6.76). GAB trace derne& values, in gmrai, are ekvateâ m p a d to the o p e r i o e e a n ~ s .
O ' O 1 2 3 4 5
Meditenanean Sea Concentration (ppb)
Mediterranean Sea Concecitration (ppb)
Figw8sLldrd6.77 Tracsekment~fromthearsad~rcharecompared to Wcsecm M a d b m m n %a vahm at 0-200m and 200-1000m depths (Fiuns 6.78 and 6-ï9 mpdWy)- Recycied met& (Cu, Ni and Cr) show a generai trend for surfaeb d@&m in bdh marine environ- whereas m i n 9 metais (Mn) exhibits a~behaubur(enhanced~SavslP,rkcroaeclwSthckpth).
(Laumond et al., 1984; Copin-Montegut et al., 1986; Saager et al., 1993; Baffi et
al., 1997; Rivaro et al., 1998). Therefore, these elements were chosen for
comparison with GAB manne envitonment. Except for Cr and Mn, the trace
elements values that are plotted in these graphs were detemined with lower
precision (Table 5.3) and their interpretation should be viewed with caution.
Cu and Cd Mediterranean Sea values, utilized in these graphs, were
reported by Laumond et al. (1 984) in a study for the Western Mediterranean Sea.
Mn and Cr concentrations were reported by Emelyanov and Shimcus (1986) as
average concentrations in Mediterranean Sea. Ni values were reported by
Tankere and Statham (1996) for Eastern Mediterranean Sea. The North Atlantic
values for Mn, Cu, Ni, Cd and Cr that were used in this were previously reported
in Sections 3.3.2 and 3.3.3.
The Mediterranean Sea and Eastern GAB levels appear to be generally
higher than the trace metal concentrations in the North Atlantic Ocean. The
comparison beîween Eastern GAB and Mediterranean trace metal values shows
that until the 1000m depth there is na signifiant difference between the trace
metal distributions of the two marine environments. It should be noted, as well,
that the Mediterranean concentrations (-ally for Cd, Mn and Ni) seem to be
fairly un i fm throughout the water colurnn, According to Boyle et al. (1985) and
Tankere and Statham (1996), the high surface trace metal levels in the
Mediterranean Sea may be a result of inMedive bidogical adivity. Specifically,
the inefficient removal of trace metais by organisrns and the low degree of
n~tfieflt re~cl ing within the Medit- iead to erihanced metal
concentrations.
Interestingly, the recycled metal b e l s in the area of research (Eastern
GAB) are higher than the North Atlantic concentrations at the same depth, even
at deep waters. This observation is consistent with the nutrient patterns
discussed previously, in Sedon 6.124, where the Eastem GA6 intemediate
water phosphate, nitrate and silicate IeveIs appeared to be enhanced cornpareci
to the N. Atlantic nutrient profiles in similar depths. As discussed previously, this
is a result of the efFect that the Southem Ocean nutrient-rich water has on the
marine chemistfy of the Eastern GAB area. This cold, dense water mas
influences the nutrient distributions and the tram element contents in the waters
of the Eastern GAB.
6.12.6 Major Elements Levels in the thme Regions
Mediterranean major element values for this companson were reported by
Emelyanov and Shimcus (1 986) as average concentrations in Mediterranean
Sea. Eastern GAB major elernent concentrations represent the mean value of the
analytical results obtained for these dements in the wnent study. North Atlantic
Ocean major element values were previwsly reported as average oceanic
values in Section 3.2. The amparison between major element average
concentrations in seawater fram the three regions (i.e. Eastern GAB,
Mediterranean Sea and North Atlantic Ocean) shows that the Eastem GAB major
element levels (especiatly Na) are only slightiy higher (Figures 6.78 and 6.79).
This observation wuld imply the intense erapcratiori processes in the swface
seawater in the Eastsm GA8 area. Haiiruiever? t f # îMee regions have similat
major element average coriceritratioris, which muid indicate that their average
12000 -
$lm-
O 2000 4000 6004 rn 1 O o o o 12000 14wo
G m t Austmlh BfgM [CI (ppm) Figure 6.18 Major Eiements in the Eastern GA0 ana are paralleied Mediterranean Sea ieveis. Na appears sîiihîly ekvated in the GAB. Generally, there is an agreement between the tm, ngioris regarding Na, Mg, Ca and S concentrations.
Figun 6.79 Major Uements in the Eastbrn GA0 a m are paralleid with Nortti Atlantic ûœan IeveIs. Na appeam rlightly ahated in the GAB. Generaüy, thetre W an agreement bdween the two rsgions ragaidirig Na, Mg, Ca and S concsntrations.
seawater salinity values are comparable, as well. In fact, the average salinity of
the seawater in the area of research is at the 35.47O0Io0 level, which is
comparable to the average oceanic salinity for the North Atlantic region (at
35.500 '1,). Further, the Meditenanean Sea waters mix with the low-salinity
North Atlantic Water, as the latter flows in aie Mediterranean basin through the
Straits of Gibraltar. In Figure 6.78, major element average concentrations in
Mediterranean waters appear to be in agreement with the average salt content in
the Eastern GAB. However, the Mediterranean waters have a uniformly high
salinity, at the 38 '1, level, according to Boyie et al. (1985), Baffi et al, (1997),
Tankere and Statham (1998). Further research could be employed in order to
define the infiuence of the Norai Atlantic Water intrusion on the average salinity
levels of the Mediterranean seawater.
CHAPTER 7
Conclusions
7.1 General
This Chapter presents the conclusions of the curent thesis project, based
on the discussion of the results.
7.2 Conclusions
1. The method used for the direct detemination of 4 major elements (Na, Mg,
Ca and S) and 17 trace elements (Mo, Pb, U, V, Cr, Mn, Fe, Co, Ni, Cd, AI,
Cs, Ba, Cu, Zn, Rb and Li) in seawater samples from the Eastern Great
Australian Bight region demonstrates good precision and accuracy for Na,
Mg, Ca, S, Mo, U, Cs, Rb, Ba, VI Cr and Mn. The results obtained for these
elements indicate that:
No pretreatment of the samples other than addification, dilution and
addition of an intemal standard is necesséuy for the double-focusing
HR-ICP-MS seawater analysis.
One element, indium (In), used as intemal standard, is sufficient to
account for instrumental drift and matrDt suppression-
Quantification by matrbcadjusted extemal calibration can effecüvely
minimize matrix interferenœs.
Although the measured values for Na, Mg, Ca, S, Mo, U, Cs, Rb, Ba,
VI Cr and Mn show good agreement with certified values, those for Pb,
Fe, Co, Ni, Cd, AI, Cu, Zn and Li were less satisfactory. Consequently,
white demonstrating the potential for direct, rapid, multi-element
seawater analysis, the method used wuld be further optimized in order
to be applicable as a routine seawater analysis for a larger suite of
analytes.
2. The Eastern Great Australian Bight marine environment is occupied by two
main water bodies at the time of the FR 03/98 Cruise in March-April 1998:
A warrn, saline surface seawater mass that occurs primarily in the
Central Great Australian BigM area and flows eastward. This water
mass extends further fmm the shore, ocarpying the surface waters
from the wast to approximately 250km distance ftom the shore. The
temperature, salinity and nutrietnt information from the seawater
samples indicate that this water body have resulted from evaporation
of a water mass that fmed from the interadion of the GA0 Plume and
a remnant comportent of the Leeuw*n Current water mass
Cold, nutrient 4ch waters that oeair below the 150m depth across the
area of research, reach the surface in coastal areas, due to upwelling
phenomena. lncrease in nutrient contents is more pronounced in
surface water samples collecteci from the eastem part of the area of
research. This cold current is also detected in subsurface layers along
the coast of Eastem Great Australian Bight. Its temperature and
salinity levels resemble the Flinders Current signature.
The correlation between the manographiwl parameters and the
analytical results for the major and trace elements of interest in the seawater
samples from the Eastem GAB condudes that:
The major element of interest profiles show that there is a positive
relationship between the increase in salinity and the concentrations of
Na, Mg, Ca and S in tfm Eastern GA6 waters. Further, these profiles
indicate a vertical mixing that occurs between the surface seawater
and deeper layers.
Recycled element conœntfatims refled the occurrence of difïerent
water masses in the region. Ba, primarily, has a pronounced nutrient - like profile that is enhanced by the presence of the nutrientn'ch
Southem Ocean water that intnides the Eastern GAB shelf.
Scavenged metal information shows that Mn concentrations have a
slight decrease with depth in rnost stations in the area of study. The
low content of dissolved Mn in the seawater samples may result from
the oxidation of the element to a less soluble Mn species, due to the
presence of highly oxygenated waters, originating Rom the Southern
Ocean, in the Eastem GAB.
The comparison between the Eastern GAB, the Mediterranean Sea
western Mediterranean) and the North Atlantic Oœan (Northwestem
Atlantic) shows that the surface waters in the Eastern GAB have
similar temperature, salinity and nutrient characteristics with the
Meditenanean environment. However, the deeper water information
ftom the area of study resembles ta the open oœan profiles
(Northwestem Atlantic).
Some trac8 element concentrations in the Eastem GAB are generally
higher than in the open ocean. Further, compared to the
Mediterranean Sea levels, the trace element contents in the area of
study show more pronounced variations with depth, whereas the
waters in the Mediterranean Sea seem to have uniform trace element
contents with depth due to intense mixing.
7.3 Recommendations
1. The results obtained for trace elernents with low concentrations in seawater
(such as Pb and Cd) could be further improved by using a preconcentration
procedure in conjunction with double focusing HR-ICP-MS. This could provide
a better understanding of their geochemical characteristics in seawater.
2. Optimization of the sample introduction system of the double-focusing HR-
ICP-MS could enhance the sensitivity of the analytical method and minimize
waterderived interferences. For example, the redudion of molybdenum oxide
interferences would improve the results obtained for Cd in direct seawater
analysis.
3. Further examination of hydrolagical data collected in dierent periods of the
year in the GAB. Combined with the findings of this thesis, such research
could allow for an overall description of the circulation of diierent water
masses in the GAB, throughout the year.
4. Comparison of the trace element levels, as detemined by the seawater
analysis in this thesis projed, with demental conœnîrations in nearshore and
offshore sediments and carbonates. This wauld provide more camplete
knowfedge of the marine geochemist~~ in oie Eastm GAB.
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Ni concentration (ppb) 0.5 1 1,s 2 2.5 3 3.5 4
Station 007, 201 m +
Typtcal Emr
Ni Standard Deviailon : 0.41 1 ppb Ni Oaedlon LimHs : 0.110 ppb
including alt stations. Due to low analytlcal precision, Ni behaviour in the GAB marine environment 1s not clear.
APPENDIX III
Pb concentration (ppb) O 0,2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Typical Error
H
Pb Standard Deviation: 0.224 ppb Pb Detection Lirnlts: 0.006 ppb
