the hcl-soluble iron, manganese, and copper contents of recent indian ocean sediments off the...

Mineralium Deposita 2, 54-61 (1967)

Short Notes

The HCl-soluble Iron, Manganese, and Copper Contents of Recent Indian Ocean Sediments off the Eastern Coast of Somalia::"

GERMAN MULLER

Labora tor ium ftir Sedimentforschung, Mineralogisch-Petrographisches Inst i tut der Universit~it Heide lberg

The HCl-soluble Fe, Mn, and Cu contents of Recent Indian Ocean Sediments off the eastern Coast of Somalia increases progressively away from the coast with decreasing grain size and carbonate content. The average Mn and Cn contents of the Indian Ocean deep-sea clay (0.56 % Mn, 0.025 % Cu, recalculated on a carbonate-free base) are between those of the Atlantic (0.40% Mn, 0.013% Cu) and the Pacific Ocean (0.94% Mn, 0.040% Cu).

In den rezenten Sedimenten des Indischen Ozeans vor der Ostktiste Somalias nehmen die salzs/iurel6sliehen Eisen-, Mangan- und Kupfergehalte vom Kiistenbereich zur Tiefsee hin bei abnehmendem Karbonatgehalt und geringer werdender Korngr6Be kontinnierlich zu. Die dnrchsehnittlichen Mn- und Cu-Konzentrationen des Tiefsee- tons aus dem Indisehen Ozean (bezogen auf karbonaffreies Material) liegen mit 0,56 bzw. 0,025 % zwischen denjenigen des Atlantischen (0,40 % Mn, 0,013 % Cu) und des Pazifischen (0,94% Mn, 0,040% Cu) Ozeans.

In troduc t ion

Recently, data on grain size, carbonate content and carbonate mineralogy of Indian Ocean sediments (channel samples of the uppermost 10 cm of the sediment cover) were publ ished (MOLLER, 1966). Prel iminary geochemical in- vest igations of Fe, Mn, and Cu on the same samples are presented below.

The concentrat ion of these elements was de- termined by atomic absorpt ion spect rophoto- metry (Perkin Elmer 303). The samples were treated with hot 2 N-HC1. Thus, all absorbed cations as well as the iron, manganese, and copper of defined authigenic iron, manganese or ferromanganese compounds and of the col-

loidal fraction of the sediment, as well as the carbonates with their typical trace elements were dissolved.

I ron in detrital silicate minerals and in oxides (hematite, magneti te) remains practically un- dissolved.

Table 1 compares the values resulting f rom HCl- t rea tment with the total concentrations obtained f rom standard silicate analysis of the whole sediment.

Table 1. Differences between add-soluble (a) and total (b) amounts of Fe, Mn, and Cu in sediments of slaliom 129 and 130 (Figures in %)

Station Fe Mn Cu No. (a) (b) (a) (b) (a) (b)

* Advanced report to "Meteor-Forschungsergebnisse, Indian Ocean Expedition 1964/65," to be published 129 in 1967/68 130

1.56 3.20 0.500 0.514 0.016 0.016 1.10 2 .29 0.078 0.084 0.007 0.008

G. M~dLLt~It., The HCI-soluble Iron, Manganese, and Copper Contents of Recent Indian Ocean Sediments 55

4z,, ° 460 A 8 0 500 5~ ° . 5~ "° , % 60

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INDIA

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le ~

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~ 40

440 460 :,8 o 500 52 ° 5 / , °

Fig. t. Sand-silt-cLay ratio of Recent Indian Ocean sediments off the eastern coast of Somalia (For exact positions of sampling stations see DIETRmH, G., et al., 1966)

560

T h e values obtained, by us ing ei ther m e t h o d for h o w e v e r , is, as to be expected, m u c h h ighe r M n and Cu are similar. T h e to ta l i ron content , than that f ound in acid- t reated samples.

56 G. MOLLER

4 4 ° 4 6 ~ 4.8 o 5 0 0 52 o 54 o

x t-.___,-~.%EN I

~ - ~ ~ ,J HHJ'.- ~ \ ' < \ , +- -

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. / . ~ ~.~'~.\~\~\~&\\ : Carbonate content(%)

N~.~ ~, ~ ~ _- ~E~ 90"75

5 6 "

440 460 480 50 ° 52 ° 540 560

12

lo 0

8 o

6 o

4 o

Fig. 2. T h e to ta l c a rbona t e c on t e n t o f the sed imen t s

Grain S ize and Carbonate Content Fig. 1 and 2 show the areal distribution of grain size and carbonate content. The sediments de-

crease progressively in grain size and carbonate content away from the coast and form zones

The HCl-soluble Iron, Manganese, and Copper Contents of Recent Indian Ocean Sediments 57

44 ° 46 ° 48 ° 500 52 ° 540 560

ARABIA

G u l f ! o f A d e n I... y .~ ' ' ~l~n

GUARDAFUI

I N D I A

A _~_ ,i ~o

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80

I N D I A N O C E A N

OBBIA

],140

MOGAD ISCHO ~ 0,890._~

Fe - c o n t e n t (%)

- - 0930---~1

44 ° 46 ° 48 ~

Fig. 3. The HCl-solublc iron content of the sediments

~ [ ] <0,5

~ 0,5-1,2

~ > 1,2

52 ° • 5.4 ° 56 °

6 °

40

2 o

0 °

2 °

(more or less parallel to the coast) of various sediment types based on different sand-silt-clay ratios and a different carbonate content.

The zone with less than 50 ~o carbonate content corresponds to the deep-sea clay facies. The areas with a silt q- clay content of more than

58 C-. Mf3LLER

4 4 o 4 6 ° 4 8 ° 5 0 ° 52 ° 5 4 ° 5 6 °

G u l f I o f A d e n

A R A B I A

AFRICA


t N D I A

OBBI,~

GUARDAFUI

8 °

6 °

~ 4 °

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Mn-conten~(p,p,m.)

~ 0-200

[ • 200-1000

~ 1000-2000

~ > 2000

2 °

2 °

4 4 ~ 4 6 ~ 4 8 ~ 5 0 ~

Fig. 4. The HCl-soluble manganese content of the sediments ~.4~ • ~6~

50% comprise the deep-sea clay and foramini- fera ooze facies; the nearshore areas with a high sand content represent the foraminiferal sand-,

the olive grey mud-, and the biogenic calcareous sand facies delineated by SC~OTT and V, STAGKELBERG (1965),


T h e Iron, Manganese, and Copper Contents of t h e Sediments

a) The Iron Content

The HCl-soluble i ron o f the sediments shows a s t rong relationship to the carbonate content: with decreasing carbonate content the i ron content increases progressively (exception: station 141). The zone with an i ron content of more than 1.2 % is practically identical with the deep- sea clay (carbonate content less than 50 %) ; the zone with Fe = 0 . 5 - 1 . 2 % corresponds to the region with a carbonate content of 50-75 % , and the zone with the lowest i ron content (less than 0 .5% can be compared with the region showing carbonate contents of more than 75 %).

c) The Copper Content

The pat tern of the copper dis tr ibut ion (values ranging f rom < 3 0 p . p . m . to 190 p.p.m.) is similar to that of the manganese content. This again shows that carbonate content and grain size are the factors control l ing the copper distr ibution.

Discussion of Results

The dis tr ibut ion of iron, manganese, and copper in the area studied follows a general geochemical dis tr ibut ion pat tern: the amounts of Fe, Mn, and Cu increase away from the coast with decreasing grain size and carbonate content.

Table 2. Average Mn and Cu contents of Indian Ocean deep-sea clays

Mn (p.p.m.) Station Carbonate Total Carbonate-free No. content [%] Sediment Sediment

Cn (p.p.m.) Total Carbonate-free Sediment Sediment

109 47.6 3510 6600 111 20.8 2150 2715 112 31.3 3070 4614 129 38.1 5000 8077 132 35.4 5100 7894 150 44.6 2000 3628

160 305 160 202 130 189 160 258 130 201 190 345

o 36.3 3472 5621 155 250

b) The Manganese Content

The manganese content increases progressively away from the coast; having its highest values in the deep-sea clay.

A comparison with Fig. 1 and 2 clearly indicates that the manganese content depends on the carbonate content and the sediment type: in the southernmost profile (stations 141-150) which shows almost no variat ion in carbonate content there is a distinct separation into different sediment types based on grain sizes with median diameters ranging f rom about 0 .1-0 ,2 mm to 0.002-0.004 m m (Mi)~Lm:, 1966). Thus, the manganese content in a coarse sediment in the southern part of the area wi th a carbonate content of only 5 0 - 6 0 % can be compared with that in a coarse calcareous sand in the north. Coarse fragments of quartz, feldspars, and other silicates have similar characteristics wi th regard to their contents of acid-soluble manganese and copper.

The very high i ron contents of station 141 (1.77%) and also - to a lesser extent - those of the neighbouring station 143 (1.15 %) probably indicates an addit ional source of the HCl-soluble i ron: A t these stations the copper content is "normal" whereas the manganese content is higher than normal, but it does not increase propor t ional ly wi th the i ron content.

The values of the Mn and Cu contents of the deep-sea d a y samples of the Indian Ocean were

Table 3. Average Mn and Cu contents (in %) of pelagic clays; comparison of the average Mn and Cu contents of 6 Indian Ocean deep-sea clays (recalculated on a carbonate-free bare) with the average content of the same trace elements in pelagic clays of the Atlantic and Pacific Ocean

Atlantic Ocean Indian Ocean Pacific Ocean (WEDEPOHL, Off Somalia (WEDEPOHL, 1960) 1960)

Mn 0.40 0.56 0.94 Cn 0.013 0.025 0.040

60 G. MOLLER

4 4 ° 4 6 ° 4 8 ° 50 ° 520 540 56 o

G u l f I o f A d e n

A R A B I A

I N D I A

GUARDAFUI

•

12

8 o


O B B I A

6 °

4 °

MOGADISCHO .,,4" I I I ' --100,~

_ _ 7 0 , , ' [ '

C u - c o n t e n t ( l : ;

[ ~ ] < 5 0

• 50-100

~ > 100

2 °

0 °

2 o

4 4 ~ 4 6 ~ 4 8 ~

Fig. 5. TheI-ICl-solublecopper content o f the sediments

recalculated on a carbonate-free base (Table 2) in order to compare these values with those of the Atlantic and Pacific Ocean (Table 3).

B2 o • 5.4 o . 56 °

"~rEDEPOHL (1960) found that some trace elements (Ni, Pb, Cu, Co, Mn and N[o) show an ap- proximately three-fold greater concentration


in t he Pacific t h a n in t he A t l a n t i c Ocean . T h i s c o u l d b e due to d i f fe ren t ra tes o f clay accu- m u l a t i o n s in b o t h oceans . ( F o r a d i scuss ion see WEDEPOHL, 1960; TUREKIAN, 1964; TUREKIAN a n d SCHUTZ, 1965; a n d o thers . )

T h e ave rage M n a n d Cu va lues o f t he I n d i a n O c e a n deep-sea clay are i n t e r m e d i a t e b e t w e e n those o f t he Pacific a n d t he A t l a n t i c Ocean . T h i s seems to i nd i ca t e t ha t a c c u m u l a t i o n o f m a n g a n e s e a n d c o p p e r in the deep-sea o f t he

w e s t e r n I n d i a n O c e a n differs f r o m t h a t in the Pacific a n d the A t l a n t i c Ocean . I n v i e w o f the smal l n u m b e r o f samples , h o w e v e r , n o final conc lus ions can b e g i v e n yet.

A c k n o w l e d g e m e n t s

The author wishes to express his sincerest thanks to the Deutsche Forschungsgemeinschaft and to Dr. H. E. RmNECK, Wilhelmshaven, for providing sample material.

R e f e r e n c e s

DIETRICH, G., K. KRAUSE, E. SEIBOLD U. K. VOLL- BRECHT: Reisebericht der Indischen Ozean Expedi- tion mit dem Forschungsschiff "Meteor" 1964-- 1965. -- "Meteor"-Forschungsergebnisse, Reihe A -- No. 1, 1--58 (1966).

MfJLLER, G. : Grain Size, Carbonate Content, and Car- bonate Mineralogy of Recent Sediments of the Indian Ocean off the Eastern Coast of Somalia. Natur- wissenschaften 53, 547--550 (1966).

SCHOTT, W., u. U. v. STACKELBERG: iJber rezente Sedi: mentation im Indischen Ozcan, ihre Bedeutung fiir die Entstehung kohlenwasserstoffhaltiger Sedimente. Erd61 and Kohle 18, 945--950 (1965).

TURE~IAN, K. K. : The geochemistry of the Atlantic Ocean Basin. Trans. N.Y. Acad. Sci. 26, 3 1 2 4 3 0 (1964).

TUREKIAN, K. K., and D. F. SCHUTZ: Trace Element Economy in the Oceans. - Sympos. on Marine Geo- chemistry, Graduate School of Oceanography, University of Rhode Island, Occ. Publ. No. 3 - 1965, 41--89 (1965).

WE~EVOHL, K. H. : Spurenanalytische Untersnchungen an Tiefseetonen aus dem Atlantik. Geochim. et Cos- mochim. Acta 18, 200-231 (1960).

Prof. Dr. G~maaN MOLLER, Laboratorium fiir Sediment- forschung, Mineralog.-Petrograph. Inst. d. Univ., 69 Heidelberg, Berliner Str. 19

the hcl-soluble iron, manganese, and copper contents of recent indian ocean sediments off the...

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