regional and seasonal variability of particle and element … · 2013. 7. 15. · regional and...

Regional and seasonal variability of particle and element-concentrations from snowpits in Antarctica

M. Kriews, S. Dietrich, D. Dick, I. Stölting, A. Wegner, H. MillerAlfred Wegener Institute for Polar and Marine ResearchAm Handelshafen 12, 27570 Bremerhaven, Germany

email: Michael.Kriews@awi.de

Introduction

Mineral dust measured in Antarctic ice cores is a unique tool

to reconstruct palaeo climate variations, but even the

knowledge about present day dust in Antarctic snow is still

very poor. In this study we analyzed different proxies of

mineral dust (particle concentration, size distribrution,

elemental composition) in snowpits from Berkner Island, a

coastal influenced site, and from Kohnen Station located on

the plateau, in order to investigate differences in the transport

behaviour of dust from the source to its deposition site and

how this might change during the year.

Fig. 1: Sampling in the snowpit at Kohnen-Station

Snowpit Kohnen-Station

75°00'S, 0°04 E, 2890 m a.s.l.

2 m deep, 2 cm resolution

season 2003/2004

mean annual accumulation rate:

62 mm w.eq

Snowpit Berkner Island

79° 34' N, 45° 39' W, 880 m a.s.l.

2 m deep, 2 cm resolution

season 2003/2004

mean annual accumulation rate:

130 mm w.eq

Experimental

Sampling

The samples were taken in polypropylen tubes, which were pressed into the snowpit walls. For the investigation of elemental composition the tubes

were precleaned in 3 different acid baths (1:4 HCl, 1:4 HNO3, 1:10 HNO3) and rinsed with ultrapure water. After sampling, the tubes were packed

into two polyethylene bags and kept frozen until analysis.

11 ppt59Co

0,4 ppt238U0,3 ppt159Tb2 ppt109Ag58 ppt58Ni

1 ppt232Th1 ppt153Eu2 ppt107Ag1,5 ppb57Fe

1 ppt209Bi1 ppt151Eu1 ppt89Y1,4 ppb56Fe

13 ppt208Pb1 ppt149Sm33 ppt88Sr0,1 ppb55Mn

11 ppt207Pb1 ppt147Sm39 ppt86Sr0,1 ppb52Cr

12 ppt206Pb0,8 ppt144Nd4 ppt85Rb15 ppt51V

6 ppt205Tl1 ppt143Nd38 ppt82Se4,0 ppb44Ca

12 ppt204Pb1 ppt142Nd0,4 ppb78Se3,6 ppb43Ca

0,2 ppt175Lu0,4 ppt141Pr11 ppt75As2,8 ppb39K

0,4 ppt174Yb2 ppt140Ce13 ppt69Ga21 ppb27Al

0,2 ppt169Tm1 ppt139La2,8 ppb66Zn1,5 ppb25Mg

0,4 ppt166Er88 ppt138Ba0,2 ppb65Cu1,8 ppb24Mg

0,2 ppt165Ho0,3 ppt115In2,6 ppb64Zn8,0 ppb23Na

0,4 ppt164Dy1 ppt114Cd0,2 ppb63Cu1 ppt9Be

1 ppt160Gd1 ppt111Cd52 ppt60Ni2 ppt8Li

MDLElementMDLElementMDLElementMDLElement

Fig. 2: Laser-sensor-setup, for particle size

and -concentration measurements

Fig. 3: Setup of full acid digestion under

pressure for sample treatment and

enrichment before ICP-MS analysis

Measurements of particle distribution

For the particle concentration and size distribution

the samples were measured within 15 minutes after

melting with a laser-sensor device (λ=670 nm). A

cross-calibration with a Coulter-Counter was made

by using samples from the EPICA deep-drilling-

sites in Dronning Maud Land and on Dome C for

particles <5 µm and samples from Greenland and

spherical particles for particle >5 µm. To determine

blank-levels ultrapure water was measured before

and after the samples. The measuring range of the

laser-sensor is between 1 and 10 µm. Each sample

was measured at least three times using a sample

volume of 4-10 ml.

Measurements of elemental composition

For determination of elemental composition the samples were processed and measured in

cleanroom laboratories at AWI. After melting the initial sample volume was approximately 20

ml. The samples were treated under pressure with a full-acid digestion (HNO3, HF, H2O2) and

enriched by a factor of 10 (fig. 3). Trace and ultrace element analyses were carried out with an

ICP-MS (ELAN 6000-Perkin-Elmer/Sciex) in combination with membran desolvatation

system MCN 6000 (Cetac) and a 100 µl PFA nebulizer. The instruments setups are shown in

table 1 and 2. As internal standard Rh was added to each sample. The method detection limits

(MDL) of the measured elements are given in table 3. The MDL depence on the method of

sample preparation and was calculated as three times the standard deviation of 91 blank

treatments.

Tab. 3: Method detection limits ( 3 σ criteria, n = 91)

Results

Particle concentration

At Berkner Island the particle concentration is low (3.75 ng/ml

without very pronounced particle peaks), we find not a clear

seasonality, but a slightly increase of particle-concentration in

winter. There are very prominent peaks at 122-136 cm depth

(year 2001), as shown in fig.4. This event is also detected in

elemental composition investigations.

At Kohnen the particle concentration is higher (6.7 ng/ml), we

find a clear seasonality in the particle-concentration with a

maximum in winter (Fig.5).

Chemical composition

Additional the concentration for Fe as a tracer for mostly

insoluble mineral dust particles is shown in fig. 4 and 5. For

Kohnen station there is a good agreement obvious in the depth

range from 16-58 and 76-96 cm.

At Berkner Island are only some few peaks for Fe which reflect

the particle distribution. The prominent peaks for particle

concentrations at 122-136 cm correspond very well with the

distribution for sea salt elements like Na, Mg, Ca (fig. 6). This

finding could not be explained yet. It could be an effect of

chemical reactions during atmospheric transport whereby

insoluble particles are produced.

1500 µsSettlingtime

DualDetector mode

10 msDwelltime

on Peakhopping

0,8 l/minAuxillary gas

15 l/minPlasma gas

onAutolens

1450 WPlasma

4,75 VLens voltage 103Rh

0,7 ml/minNebulizer gas

SetupParameter

~ 100 µl/minSample uptake rate

18 ml/minNitrogen flow

1,88 l/minArgon flow

SetupParameter

Tab. 1: MCN 6000 parameters Tab. 2: ELAN 6000 parameters

Depth[cm]

0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 144 152 160 168 176 184

Concentr

ation [ppb]

0

10

20

30

200

Delta 1

8O

[‰

]

-40

-35

-30

-25

-20

-15

2004 2003 2002 2001 2000

Age [a]

Particle concentration [ppb]

Delta 18

O [‰]

Fe [ppb]

23Na

Ko

nz.

[ppb

]

0

400

800

1200

1600

25Mg

Konz.

[pp

b]

0

50

100

150

200

44Ca

Konz.

[pp

b]

0

20

40

140Ce

Ko

nz.

[ppb

]

0,00

0,020,100,120,14

142Nd

Ko

nz.

[ppb

]

0,000

0,005

0,010

208Pb

depth (cm)

0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 144 152 160 168 176 184

Konz. [p

pb]

0,00

0,05

0,10

Concentration with error

Instrument detection limit (aligned)

Method detection limit (aligned)

Fig. 4: Particle and Fe concentration as well as Delta 18O

(temperature proxy) at Berkner Island

Fig. 6: Na, Mg, Ca (sea salt), Ce, Nd (mineral dust) and Pb

(anthropogenic) concentration at Berkner Island

2004 2003 2002 2001 1997 19962000 1999 1998 1995 1994

Age [a]

Depth [cm]

0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 144 152 160 168 176 184 192 200

Con

cen

tration [

ppb]

0

5

10

15

20

25

30

100

Delta

18

O [

‰]

-60

-55

-50

-45

-40

-35

-30

Particle concentration [ppb]

Delta 18O [‰]

Fe [ppb]

24Mg

Con

c. [

ppb

]

0

5

10

15

20

25

70

23Na

Conc. [p

pb]

0

40

80

120

300

44Ca

Co

nc.

[pp

b]

0

20

40

60

140Ce

Co

nc. [p

pb]

0,00

0,01

0,02

0,03

0,04

0,05

142Nd

Co

nc. [p

pb]

0,00

0,01

0,02

0,04

208Pb

Depth (cm)

0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 144 152 160 168 176 184 192 200

Con

c. [

ppb

]

0,0

0,1

0,2

0,6

Concentration with error

Instrument detection limit (aligned)

Method detection limit (aligned)

Fig. 5: Particle and Fe concentration as well as Delta 18O

(temperature proxy) at Kohnen station

Fig. 7: Na, Mg, Ca (sea salt), Ce, Nd (mineral dust) and Pb

(anthropogenic) concentration at Kohnen station

Tab. 4: Mean element concentrations with standard deviation as well as min. and max.

values for snowpits as well as the deposition rate at Kohnen station and Berkner Island

From tab. 4 it is obvious that the mean con-

centrations for sea salt elements are higher at

Berkner Island, while the mineral dust tracer

show higher values at Kohnen. Anthropogenic

tracer elements show slightly higher concentrations at Kohnen. All elements show a high variability.

This strong variabilty is also

shown for some selected ele-

ments in fig. 4-7. There is a

clear seasonality in the sea-salt

elements at Berkner Island.

At Kohnen sea salt-aerosol is

not the dominating source,

but shows also a seasonality with

maxima in winter.

Mineral dust aerosol is the dominat

source at Kohnen and shows a clear

seasonality with maxima in winter.

Taking into account the yearly

accumulation rate it can be seen

from tab. 4 that the flux for sea salt

aerosol is by a factor of 8-15 higher

at Berkner Island than on the plateau

at Kohnen. For mineral dust as well

as for anthropogenic elements the

deposition rate at both stations is

nearly similar whereas there is a

slightly higher amount at Kohnen.

0.0780,2 ppt15 ppt0,01 ppt0,6 ppt0.0500,2 ppt19 pptn.d.0,8 ppt238U

0.210,2 ppt15 ppt0,09 ppt1,6 ppt0.0810,2 ppt27 pptn.d.1,3 ppt232Th

0.0260,2 ppt11 pptn.d.0,2 ppt0.130,3 ppt27 pptn.d.2,1 ppt209Bi

2.10,9 ppt0,2 ppb0,1 ppt16 ppt3.21,2 ppt0,6 ppbn.d.51 ppt208Pb

0.290,3 ppt10 pptn.d.2,2 ppt0.440,8 ppt30 pptn.d.7,1 ppt205Tl

0.0260,2 ppt2,8 pptn.d.0,2 ppt0.0430,1 ppt18 pptn.d.0,7 ppt175Lu

0.0390,2 ppt2,9 ppt0,04 ppt0,3 ppt0.0560,2 ppt19 pptn.d.0,9 ppt174Yb

0.0260,2 ppt2,8 pptn.d.0,2 ppt0.0370,1 ppt17 pptn.d.0,6 ppt169Tm

0.0390,2 ppt2,9 pptn.d.0,3 ppt0.0560,1 ppt19 pptn.d.0,9 ppt166Er

0.0260,2 ppt2,8 pptn.d.0,2 ppt0.0430,1 ppt17 pptn.d.0,7 ppt165Ho

0.0390,2 ppt3,6 pptn.d.0,3 ppt0.0560,1 ppt20 pptn.d.0,9 ppt164Dy

0.0390,2 ppt3,1 pptn.d.0,3 ppt0.0560,1 ppt19 pptn.d.0,9 ppt160Gd

0.0260,2 ppt2,9 pptn.d.0,2 ppt0.0370,1 ppt17 pptn.d.0,6 ppt159Tb

0.0390,2 ppt3,1 pptn.d.0,3 ppt0.0370,1 ppt17 pptn.d.0,6 ppt151Eu

0.0650,2 ppt3,2 pptn.d.0,5 ppt0.0560,2 ppt18 pptn.d.0,9 ppt147Sm

0.180,3 ppt18 ppt0,2 ppt1,4 ppt0.180,2 ppt39 ppt0,1 ppt2,9 ppt143Nd

0.0650,2 ppt5,5 ppt0,02 ppt0,5 ppt0.0810,1 ppt20 pptn.d.1,3 ppt141Pr

0.830,3 ppt0,1 ppb0,6 ppt6,4 ppt0.930,3 ppt0,6 ppb0,5 ppt15 ppt140Ce

0.390,3 ppt63 ppt0,2 ppt3,0 ppt0.420,2 ppt0,3 ppb0,2 ppt6,8 ppt139La

26.04,8 ppt5,8 ppbn.d.0,2 ppb24.86,6 ppt14 ppb3,7 ppt0,4 ppb138Ba

0.0390,2 ppt15 pptn.d.0,3 ppt0.0500,1 ppt17 pptn.d.0,8 ppt115In

0.520,6 ppt20 pptn.d.4,0 ppt0.811,8 ppt0,1 ppbn.d.13 ppt114Cd

0.360,2 ppt13 pptn.d.2,8 ppt0.510,2 ppt0,1 ppb0,5 ppt8,2 ppt109Ag

0.210,2 ppt25 ppt0,1 ppt1,6 ppt0.180,1 ppt29 ppt0,05 ppt2,9 ppt89Y

265,4 ppt1,3 ppb14 ppt0,2 ppb3.11,2 ppt0,3 ppb0,4 ppt50 ppt86Sr

1.20,7 ppt35 ppt1,8 ppt9,1 ppt5.20,3 ppt48 ppt1,3 ppt84 ppt85Rb

2.50,7 ppt0,5 ppbn.d.19 ppt2.30,6 ppt1,2 ppbn.d.37 ppt69Ga

6.84,3 ppt1,3 ppbn.d.52 ppt6.25,4 ppt1,4 ppbn.d.0,1 ppb65Cu

5330,1 ppb12 ppb1,2 ppb4,1 ppb86810 ppb105 ppb2,7 ppb14 ppb64Zn

0.950,5 ppt85 pptn.d.7,3 ppt0.870,3 ppt0,1 ppbn.d.14 ppt59Co

8.21,6 ppt0,8 ppbn.d.63 ppt6.22,5 ppt1,4 ppb2,8 ppt0,1 ppb58Ni

37757 ppt50 ppbn.d.2,9 ppb2540,1 ppb52 ppb0,6 ppb4,1 ppb56Fe

3.41,8 ppt0,4 ppbn.d.26 ppt6.24,3 ppt1,7 ppbn.d.0,1 ppb55Mn

8.54,5 ppt0,8 ppbn.d.65 ppt12.48,2 ppt1,9 ppbn.d.0,2 ppb52Cr

3.33,9 ppt0,9 ppbn.d.25 ppt2.52,8 ppt0,8 ppbn.d.41 ppt51V

14300,3 ppb53 ppb1,0 ppb11 ppb4840,2 ppb94 ppb0,7 ppb7,8 ppb44Ca

14300,3 ppb66 ppb0,6 ppb11 ppb17470 ppt10 ppbn.d.2,8 ppb39K

7410,2 ppb459 ppbn.d.5,7 ppb26048,8 ppb1015 ppbn.d.42 ppb27Al

37701,0 ppb176 ppb1,1 ppb29 ppb4900,2 ppb65 ppb1,4 ppb7,9 ppb24Mg

276907,6 ppb1491 ppb8,2 ppb213 ppb16740,7 ppb327 ppb68 ppt27 ppb23Na

0.0330,2 ppt9,5 pptn.d.0,25 ppt0.0430,2 ppt18 pptn.d.0,7 ppt9Be

0.730,5 ppt63 pptn.d.5,6 ppt0.400,4 ppt44 ppt0,5 ppt6,4 ppt8Li

Flux (µg m-2 a-1)Std. dev.Max.Min.AverageFlux (µg m-2 a-1)Std. dev.Max.Min.AverageElement

Berkner IslandKohnen

In contrast to Berkner Island we found at Kohnen

only a good correlation for Na and Mg. For all

shown elements the seawater ratio could not be

found. The reason might be fractionation effects

during atmospheric transport or there are other

sources.

To identify possible other sources e.g. for Na and Ca the non sea salt Na and Ca-

concentration (nss-Na, Ca) was calculated. Fig. 8 c shows the results. At Kohnen

most of the Ca is not from a marine source, while for Na except some few depths

more than 90% is from sea salt. At Berkner Island except some few depths more

than 90% of the total Ca and nearly 100% of Na is from an oceanic source.

Fig. 8a: Correlation of Na versus , Mg, Ca,

Sr at Berkner Island

Na/K

Concentration K [ppb]

0 10 20 30 40 50 60 70

Co

nce

ntr

ati

on N

a [

pp

b]

0

200

400

600

800

1000

1200

1400

1600

r ²=0,9843

Na/Sr

Concentration Sr [ppb]

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

Concen

tration

Na [p

pb

]

0

200

400

600

800

1000

1200

1400

1600

r ²=0,9547

Na/Mg

Concentration Mg [ppb]

0 50 100 150 200

Concen

tration

Na [p

pb

]

0

200

400

600

800

1000

1200

1400

1600

r ²=0,9537

Na/Ca

Concentration Ca [ppb]

0 10 20 30 40 50 60

Co

ncen

tration N

a [p

pb]

0

200

400

600

800

1000

1200

1400

1600

r ²=0,7874

0 25 50 75 100 125 150 175

Co

nc

. [

ppb

]

0

10

20

30

40 nss-Ca

total-Ca

depth [cm] depth [cm]

0 50 100 150 200

Con

c. [p

pb]

0

20

40

80

total-Ca

nss-Ca

depth [cm]

Berkner Island

0 25 50 75 100 125 150 175

Co

nc.

[p

pb

]

0

200

400

600

800

1000

1200

1400

nss-Na

total-Na

Kohnen

depth [cm]

0 50 100 150 200

Conc. [p

pb

]

0

50

100

350

total-Na

nss-Na

Na/K

Concentration K [ppb]

0 2 4 6 8 10 12

Con

centr

atio

n N

a [p

pb

]

0

50

100

150

200

250

300

350Na/Sr

Concentration Sr [ppb]

0,00 0,05 0,10 0,15 0,20 0,25 0,30

Conce

ntr

atio

n N

a [p

pb]

0

50

100

150

200

250

300

350

Na/Mg

Concentration Mg [ppb]

0 20 40 60

Co

ncentr

ation

Na [

pp

b]

0

100

200

300

Na/Ca

Concentration Ca [ppb]

0 10 20 30 40 50

Con

centr

ation N

a [

ppb

]

0

50

100

150

200

250

Ocean water ratioOcean water ratio

Fig. 8b: Correlation of Na versus

Mg, Ca, Sr at Kohnen station

From fig. 6 it can bee seen that at Berkner Island is a good

agreement in the depth profile for the sea salt elements Na, Mg

and Ca. At Kohnen station (fig. 7) the profile for Ca is often

different. In fig. 8 a and b the Na concentration is plotted

versus typical other sea salt elements (Mg, Sr, Ca). For

Berkner Island it can be seen that there is a good correlation

between these elements and Na and the element ratios (marked

by a red cross) in open ocean water agree very well.

Fig. 8c: Total and non sea salt (nss) Na and Ca

Conclusions and Outlook

The plateau position at Kohnen

Station has a clear seasonality in

dust concentration. The chemical

composition shows that mineral dust

is dominating. At Berkner Island the

particle concentration and size

distribution is dominated by single

events, that might have a local

source. A strong influence from the

ocean could be observed when

looking to typical sea salt tracer

elements.

For future investigations of

deep ice cores it is necessary

to take into account at which

position the drilling will be

carried out. In ice core

studies up to now Ca is used

as a tracer for mineral dust in

contnious flow analyses. This

contribution shows that

depending on the sampling

location Ca has at least two

different sources.

In further steps analyses will be carried out for samples from potential sources in the southern

hemisphere to identify sources and possible changes during the year. For this analyses the Rare

earth element distribution patterns will be used.

Acknowledgement

This work is a contribution to the “European Project for Ice

Coring in Antarctica” (EPICA), a joint European Science

Foundation/European Commission (EC) scientific program,

funded by the EC under the Environment and Climate Program.