1998 - Sea Salt Aerosol in Coastal Antartic Regions

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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. D9, PAGES 10,961-10,974, MAY 20, 1998

Sea-saltaerosol n coastalAntarctic regions

D. Wagenbach,F. Ducroz, R. Mulvaney, L. Keck,M. Legrand, J. S. Hall, 3 and E. W. Wolff 3

• A. Minikin, TM

Abstract. Continuous ear round recordsof atmospheric ea-saltconcentrations avebeen recoveredat three coastalAntarctic stations Halley, Dumont D'Urville, andNeumayer) at temporalresolutions ypicallybetween 1 day and 2 weeks.The recordswereevaluated n terms of their spatialand seasonal ariabilityas well as with respect ochangs n the relative on compositionf airbornsea-salt articles. nnualmeansea-saltconcentrationsarybetween400ngm 3 at Dumont 'Urville, 50ngm 3 at Neumayer,and200ng m 3 at Halley, espectively.heyare hus onsiderablyower han he meanlevelspreviouslyobservedat the north tip of the Antarctic Peninsulabut are, at theirlower end, comparable o the level previously eported from Mawson.Therepresentativenessf the atmospheric ea-saltdata appears o be weak due to their hightemporalvariability,strong mpactsof site specificaspects suchas site topography)butalso due to the nonuniformsampling echniquesapplied so far. In accordancewith the icecore evidence, he seasonal hange n the atmospheric ea-salt oad is found to be clearly

out of phasewith the seasonal ycle of the open water fraction offshore rom the stationas (with the exceptionof Dumont D'Urville) the lowestconcentrations re generallyobservedduring the local summermonths.Major ion analyses f bulk aerosolandconcurrentlyampledresh now how strong, ystematicepletionf the SO]- to Na+(C1-) ratioswith respect o bulk seawater, which appeared o be confined o the localwinterhalfyear.During hat ime,sea-salt O]- was ound o be depletedypicallyy60-80% alongwith a concurrent a+ deficit,which s in accordanceith the precipitationof mirabilite. o significantractionationf Mg2+, K+, andCa2+ between eawater ndsea-saltarticless observed.aboratoryxperimentsailed o simulatehe SO•-fractionation n airborne seawaterdropletsor in the skin of seawaterbubblesat low airtemperatures.heygave, owever, O]- depletionactors, imilar o the fieldobservationin air and snow, n the remainingbrine of seawaterwhich was partly frozen below -8øCto an artificial sea ice surface. t is suggestedherefore that the mobilization of brine fromthe sea ce surfaceconstitutes n important sea-saltsource n winter which may dominate

the atmosphericsea-salt oad at high latitudes of coastalAntarctica.

1. introduction

Sea-salt particles produced by bubble bursting and wavecrest disruptionsprovide by far the largest flux of primaryaerosolparticles o the marine atmosphere.The supramicronfraction of the marine aerosolbody is controlled therefore by

this oceanic source eading to boundary ayer loads around

2-50 tzgseasaltper m3 which arystrongly s a function fwind speed Fitzgerald, 991]. Interest in atmospheric ea-saltparticleswas recently eneweddue to their potential contribu-tion to the indirect adiative orcing Larhamand Smith,1990],as well as from their role in a series of heterogeneousair

chemicalprocesses s responsibleor large fluxesof HC1 and

1Institutiir Umweltphysik,niversity f Heidelberg, eidelberg,Germany.

2LaboratoireeGlaciologiet Gdophysiquee 'EnvironnementuCentre National de la RechercheScientifique,St. Martin d'Hares,France.

3British ntarcticSurvey, aturalEnvironment esearch ouncil,Cambridge,England.

4Now t AlfredWegenernstituteor PolarandMarineResearch,Bremerhaven,Germany.

Copyright1998 by the American Geophysical nion.

Paper number 97JD01804.0148-0227/98/97JD-01804509.00

HBr [Mclnnes et al., 1994; Mozurkevich,1995], but also ofreactive halogens [Vogt et al., 1996], to the remote marine

troposphere.n the contextof the Antarctic roposphere, ea-salt particlesare the only primary aerosolsproduced n rele-vant quantitieswithin he southpolar cell.They may add there-fore a substantial raction of seawatersulphate o the more

interestingdimethyl sulfid derived sulphate nventory of thisregion. This contribution has to be estimated accuratelyvia

other seawaterspecies.Further interest n Antarctic sea salt

comes about since the Antarctic NHx, level is normally ex-

tremely low [Legrandet al., this issue].Sea salt thus provides

during modern times the only important alkaline counterpartto the otherwisedominating acidic componentsmade up by

non-sea-saltNSS)biogenic O42-,methanesulfonateMSA),and HNO 3. When sea-saltparticlesbecomeexternallymixedwith these species Parungo t al., 1986], additional pathways

mayexist o carrybiogenic ulphur nd nitratedown o the icesheetsurface Moseret al., 1990].

A relatively arge data set on the sea-saltcontentof modern

and pastAntarcticprecipitationhasbeen recovered rom var-ious ce core studies Legrand nd Delmas,1988;Clausen ndLangway,1989;Delmasand Legrand,1989]. The clear ice coreevidence for higher sea-salt levels during glacial times was

generally nterpreted as indicatingan intensifiedsea-saltpro-

ductionassociated ith higher cyclonic ctivity higher storm-

10,961



10,962 WAGENBACH ET AL.: SEA-SALT AEROSOL IN COASTAL ANTARCTIC REGIONS

iness)overcompensatinghe much arger sea ce extentduringthat time [Petitet al., 1981]. Similarly, he sea-salt ariabilityover the last 200 years has been attributedby Peel and Mulv-

aney [1992] to concurrentchange n the regionalsea ce andcirculation pattern. Year-round observations f atmosphericsea-salt concentrations that would be needed to corroborate

these pictures are, however, sparse.Discontinuous ecordsfrom South Pole over the years 1979-1983 are the only suchdata from central Antarctica and were extensivelyused tostudy the episodic ntrusion of maritime air masses o the

plateau [Bodhaine t al., 1986]. At coastalAntarctica,wherethe sea-salt source of the polar ocean is seen much more

strongly, ecords xists ack to 1983 at Neumayer Wagenbachet al., 1988]and back o 1987at Mawson Prosperot al., 1991].They are supplemented y shorter observations t the tip ofthe Antarctic Peninsula Savoieet al., 1993] which are, how-ever, ess epresentativeor the marginal ce sheet egions.Asreviewedby Wagenbach1996], no conclusive icturecouldbederived so far from these records on their link to the annual

sea ce cycle,making he principalsourcearea responsibleorhighly elevated sea-saltconcentrationsduring winter essen-tially unknown.Furthermore, here is still a serious ncertaintyabout he occurrence nd the underlyingprocesseading o theenormousdepletionof sulphate n airborne sea-saltparticlesseen in aerosol and precipitation at almost all coastal sites[Legrandand Delmas, 1985; vey et al., 1986; Gjessing, 989;Mulvaneyand Peel, 1988;Wagenbacht al., 1988;Minikin et al.,

1994]. In a collaborative ffort the aerosolchemicalobserva-

tions at Neumayer NM) have been extended o the stationsHalley (HB for Halley Bay) and Dumont D'Urville (DDU) inorder to increase he spatialcoverage f suchobservationsnd

to deducea detailed picture on the link betweenatmospheric

and glacio-chemicalhangesWolffetal., this ssue a)]. In thispaper the atmospheric ea-salt ecords ecoveredat thesesta-tions will be discussedmainly in terms of their spatial and

seasonal ariabilityas well as with respect o the apparentsulphate ractionationobserved etweenairbornesea-salt ar-ticles and seawater.

2. Sampling Sites and Methods

A general overview of the climatologicalsituation at allthree sitesunder investigations given by K6nig-Langlo t al.[this ssue].Sampling echniques nd analyticalmethodsusedby the differentgroups nvolvedare summarized y Wolflet al.

[this ssue a)]. In the followingsection,only a brief outlineoftheseaspectss presented, oncentrating n details elevant orthe sea-saltcomponentof the Antarctic aerosolbody. n Fig-ure i the geographical ocationsof the stationsare shown

togetherwith a zoomedview of their position elative to the(mean) coast ine and the prevailingwind direction.Detailsonthe site specific ampling nd analytical echniquesor sea-saltaerosol are given n Table 1.

NM and HB which are both situated on ice shelves of the

Atlantic sector are subject o a similar surfacewind patterndominatedby zonalwindsmost requently rom easterlydirec-tions. Apart from the lower mean annual wind speed at HB(6.2 m s • versus .9 m s • at NM), the following aindis-tinguishing eaturesmay be relevant or the local atmosphericsea-salt oad as (1) the more southerly ositionof HB (by 5ø)leading o a shorterand delayedopen water season swell as

to a relativelyhigh sea ce fractionduringsummer nd (2) thegenerally larger distance o the ice edge at HB which may

decrease he influence of the very local sea-saltsource. For

example, he ice shelf fetch for the most frequent easterlywindsat NM maybe as ow as 6.5 km, whereasgoingeastwardfrom Halley, no regional ce edge s reached.

DDU differs considerablyrom the situationof the two iceshelf stations n being placed on a small sland 1 km offshorefrom the coastlineand in being subject o strongmeridionaldownslopewinds throughout the year (mean annual wind

speed9.5 m s-•). For a detailed escriptionf the site,seeLegrand t al. [this ssue].Because f its positionat 66øS n thePacificsector,a longer open water season nd a smallermax-

imum sea ce extent s seenat DDU in comparison o HB and

NM. Hence the general conditions or aerosol samplingat

DDU are quite similar to those at Mawson (Indian Oceansector)where aerosol-chemicalecordswere previouslyob-tained by Savoieet al. [1993] over several ears.

Aerosolcollectionwas achieved t HB and DDU by contin-uous ow volume samplingusingopen-face ilter holderspro-

tected by a wind shield. n contrast o NM, no interruptionofthe sampling procedure related to wind direction or wind

speedwas applied here. At NM, aerosol samplingwas per-formed in a specialclean air satellitestation as described yWagenbacht al. [1988]with no major changes xcept hat thestation was moved in 1992 8 km to the southeast and that a

newly constructedclean air station was established here in

1994 essentially pplying he samesampling echnique.On thebasisof the differentsamplingmethods utlined n Table 1, thefollowingsystematic ffectsmay be important n assessinghecomparabilityof the sea-salt oadsobserved t the three sites:

1. Becauseof the relatively large geometric mean massdiameter of locallyproducedsea-salt erosolof the order of 10

•m [O'Odowed t al., 1997], he particlecutoffof the air intakesystems ritically controls the observedsea-salt oad. Sinceisokineticsamplingcould not be applied, sea-saltconcentra-tions are expected o be generallyunderestimated, specially

duringhighwind speeds.At NM (where an actively entilatedhigh volumestackoperates s a kind of virtual impactor) heparticle cutoff diameter is empiricallyestimatedat around 6•m suggestinghat the large sea-saltparticle mode is notcompletelysampled.

2. No such information is available for the HB and DDU

open-face samplingsystems, ut the much lower filter face

velocityappliedhere (if compared o the NM sampling ead)suggestsn even ower cutoff diameter,especially uringhighwind speedevents.At all three sites,aerosolscavengingn thenear-surfaceayerby drifting snowmight further contribute othe underestimation f the ambientsea-salt evel.Beingmainly

dependenton the site specific nowdrift frequency e.g., 40%at NM), this effect is expected o be less mportantat DDU

(island position), especiallyduring summer. On the otherhand, or a givencomparable nowdrift situation,NM data areleast affectedsince he air intake is placedat 7-9 m above hesnow surface instead of 2 m at the other sites and since the

pumpsare automatically witchedoff during heavysnowdriftperiods.This fractionatingsampling t NM provides he mostobvious difference from the otherwise continuous collection

modesat HB and DDU because ituationswith extremelyhighor lowwind speeds swell aswith northerlywinds putting he

samplingsite downwind rom the main station) are a prioriexcluded.

Laboratories n charge of the designof the collectionpro-cedureand sampleanalyses ere the British Antarctic Survey

for HB, the Laboratoire de Glaciologieet G•ophysiquede



WAGENBACH ET AL.: SEA-SALT AEROSOL IN COASTAL ANTARCTIC REGIONS 10,963

HB5

Icehelf

Ice Sheet

Atka Bay

ß

.

GVN ß

NM ©

Ekstrmmce helf •) .• 1'0m

DDU

I

Figure1. Positionf samplingitesn coastal ntarcticaithyear-roundhemicalerosolecords.inesover oceanareas ndicate he 50% sea ce coverage uringwinter (dash-dottedines)and duringsummer(dottedines),espectivelyadoptedromGiovinettondWaters1990]. iteseferringo thiswork reshownin detailwith espectotheir oastlineopographyndmainwinddirectionarrow). VN denoteshe ormerGeorg onNeumayertation, B4 s he1991 ndHB5 s he1992 amplingites t HalleyBay, ndDDUis the Dumont D'Urville station.

l'Environnement or DDU, and the Institut ffir Umweltphysik

for NM. The precision f thesea-salt eterminationalculatedvia onicseawater pecies a+ or C1- aremainly ontrolled tDDU and NM by the analytical ncertainty f the ion chro-

matographyroceduretypicallyess han _+5% at all sites)since the filter blank contributioncould be neglectedhere.

AlthoughocalK+ andCa + contaminationy soilparticlesfrompenguin roppingsccur t DDU, sea-saltoncentrations

Table1. SamplingndAnalysesethodsf Atmosphericea-Saltpeciest theCoastal ntarctic tationsumontd'Urville, Halley, and Neumayer

Dumont d'Urville Halley Bay Neumayer66øS, 40øE 75øS, 6øW 70øS, øW

Observational eriodCollection interval

Sampling ystemAir intake heightAerosol filter

Filter face velocityAnalyzedsea-salt pecies

and methods

Jan. 1991 to Dec. 1995 Feb. 1991 to Feb. 1993

1-7 days 1-2 days

1.8 m above snow level

47 mm •, 0.4/xm teflonopen face0.6 ms -•

Na+, K+, Mg2+,Ca +,SO42-, I-, Br-'ion chromatography

2 m above snow level

37 mm •, 0.8/xm cellulosemembraneopen face0.4 ms -•

Na+, Mg2+b: lameatomic bsorption,so4-:

ion chromatography

March 1983 to Jan. 1996

3-20 days typical2 weeks)

7 m above snow level

240 mm •, double cellulose iltersin line

1.1ms -•a

Na+, K+, Mg2+,Ca +,SO42-, I-, Br-:ion chromatography

aCorrespondso 13% of air intakevelocity.bCations vailable or 1991only.



10,964 WAGENBACH ET AL.' SEA-SALT AEROSOL IN COASTAL ANTARCTIC REGIONS

derivedvia Na + or C1- are shown o be unaffected y suchevents Ducroz,1996].At HB, due to the relatively ow sea-saltlevel and the shortsampling ntervals, he filter blank variabil-ity was found to be substantial, eading to 15% of samples

falling elow he meanC1- detectionimitof about ngm 3C1- (defined as twice the standarddeviationof C1- blanks).For all sites he extractionefficiencyof the filters for seawaterions s very close o 100%; hence no correctionswere applied.

Again, a 100% collectionefficiencywas assumed or HB andDDU membrane filters. At NM the double Whatman filters

arranged ace to face were individuallyanalyzed o correct orparticlepenetrations of the first filter) whichwere found o bearound 10% except or filters occasionally etted by snoworrime.

3. Atmospheric Sea-Salt Records

In view of the very different sampling ntervals anging rom1 day at HE, up to 7 daysat DDU, to typically2 weeksat NM,

the continuous aw data of each site were formally collapsed

into continuousseriesof 10 day meansmaking their temporal

variabilitymore comparable.At HE, C1- wasused o infer thesea-saltconcentrations incecation analyseswere available or

1991 only. At DDU and NM the commonlymore conservative

Na+ (seesection ) wasused nstead. he Na+ andC1- data,respectively, re then expressed s sea-saltconcentration iathe bulk seawater (ESW) content given by Witson [1975].Where possible, ll referencesmade to other Antarctic sea-saltdata are basedon Na+, or alternatively n C1-. To make theatmospheric bservations s comparable spossible o ice coreresults,mean concentration aluesare given n the text gener-ally as arithmetic means.

3.1. Intersite Variability

Atmosphericsea-salt ecordsover the years 1990-1995 aredisplayedat 10 day means for all three stations n Figure 2.Common to all sites s the relatively high sample nterval to

sample nterval variabilityoccurring hroughout he year (for

details,see descriptive tatistics f 10 day meansgiven n sec-tion 3.2). This behaviorof the atmospheric ea-saltsignal sseen also at other Antarctic stations Savoieet at., 1993] in-cludingSouthPole [Bodhaine t al., 1986]. t is expected here-fore that the episodicpropertiesof this signalmay be drivenboth by rapidly changingproductionrates and by varying at-mospheric ransportsituations. he obviousdifferences n thecoastal records are the much lower mean level at HE in com-

parison to the more similar ones of NM and DDU, and theoutstanding ummermaximum only seen at DDU. The latterfinding may be explainedby the unique slandpositionof this

samplingsite, generallynot more than some 100 m downwindfrom open water during December to March. The missing1994/1995 summerpeak supports his view since during thatseason exceptionallysevere sea ice conditionsprevailed atDDU until midsummer.

The relativelyowsea-saltevelat HE of 200ngm 3, fallingbelow the respectivemeansat NM and DDU by a factor 4.4and 7, respectivelysee Table 2), is more difficult to explain,however. In contrast to the other sites, no vast open waterareas exist offshore rom HE during summersuggestinghatthe difference o NM and especially o DDU during that sea-son is due to a reduced local sea-salt source. However, similar

intersite sea-saltgradientsbetween HE and NM or DDU pre-

vail during the whole winter seasonwhen no such arge differ-

lOOO

800600

400

200

0

HB

6OOO

4500

3000

1500

0

I DDUi

I

I

I

I I

I

' I , I, I, I,3OOO

2000 •

1500 • •

oooI I I

500

1991 1992 1993 1994 1995

i NM

1996

Figure 2. Atmosphericsea-salt ecordsdisplayedas 10 daymeans for the overlapping sampling periods at Halley Bay(HE), Dumont D'Urville (DDU), and Neumayer NM).

ences n the local open water fraction are expected.Referringto the site climatologies ivenby K6nig-Langto t at. [this s-sue],NM is subject o a 20% frequencyof blowingsnowdays(i.e., heavysnowdrift aboveeye level), whereasonly 6% arereported for HB, respectively. his might explain part of the

discrepancyompared o the NM sea-saltevel asconnectedoa difference n cyclonic ctivity.On the other hand, the sea-salt

observations t 1-2 day intervalsat HB are not significantly

correlatedwith the localwind speedand show, nstead, hat thevery highestsea-saltconcentrations ccureven during moder-ate winds.As addressedn section2, the much onger ce shelffetch during onshorewinds at HB (confinedhere to westerly

oneswhich are relativelyweak and less requent) may be oneimportantreason or the much ower sea-salt oncentrationsfcompared o NM. However, sinceat both stations irtually hesamesea-salt evels n fresh (surface)snoware observed, lso

differencesn the aerosolsampling ystemsdescribedn sec-tion 2) may be responsibleor the intersitediscrepancy.

Inspectionof the geographical istributionof the mean at-mospheric ea-salt evel in Antarcticasummarized n Table 2

(in comparisonwith relevant ce core data) revealsa ratherlarge spatialvariabilityamongcoastalsitescoveringa rangeof200 ng m 3 at HB to 10,000ng m 3 at MarshStation. helatter value is difficult to assess,however, since no details on

the sampling ite and collectionprocedureare givenby Savoieet at. [1993]. t wouldbe hard to predicta typicalatmospheric



WAGENBACH ET AL.' SEA-SALT AEROSOL IN COASTAL ANTARCTIC REGIONS 10,965

Table 2. GeographicalDistribution of Mean Sea-Salt Concentrations n Coastal AntarcticAir and Snow

Site, Elevation, Distance to Coast, Air,-3

øS m asl km ngm

Snow, g g- •

Surface Snow Firn Cores

Weddell Sea sector

Halley (75ø) 10 15 200

Ronne Ice Shelve 77ø-81 ) -80 50-200 -..Berkner sland (79ø) 700-900 50-150 .-.Atlantic sector

Neumayer70 ) <42 10 850Ekstr0m ce Shelve -71 ø) <100 30-100 .-.RitscherHochland -79 ø) -1,000 200-300 ...

Pacific sector

Dumont d'Urville (66ø) 5 <1 1,400D10 (66ø) 270 4 ...

Other stations

Mawson68ø) <1 330Palmer65 ) coastal ite 3,900Marsh 62ø) coastal ite 10,000SouthPole (90ø) 2,800 >1,500 62g

1.4 a 1.7 a

ß . 1.6_0.7bß . 1.9_1.0 c

1.7 40 e

ß . 2.0 e

ß . 0.5_0.2 e

90 ...

. . . 0.8 g

ß . 0.03

Surfacesnow denotes resh snow sampledconcurrently o atmosphericobservation.aWolffet al. [this ssue b)].bMinikin t al. [1994].CWagenbacht al. [1994].dRefers to 1983-1995.

eMoser 1991].fDucroz1996] sampled uringwinterseasonsnly).gLegrand t al. [this ssue].hSavoiet al. [1993].iTuncelt al. [1989].

sea-salt oncentration or each specific ite from their positionrelative o the relevant arge scalephenomenaalone (suchassea ice edge, main storm tracks,or regional wind systems) fthe very ocal situationhas he major control on the occurrence

of high sea-saltevents.There are several examples or suchlocal impacts:DDU and Mawson, althoughexperiencing im-

ilar downslopewinds, differ by a factor of 4 in their meanwinter sea-saltevel seealso he discrepancyetweenNM andHB addressed bove). Similarly, concurrentsamplingsper-formed on the DDU archipelago km apart by Ducroz [1996]showsystematic ea-salt oncentration ifferences n the range

of a factor 2 over a 6 week period in January.There are also

doubtson the spatial and temporal representativenessf theatmosphericobservations iven the extremely high sea-saltconcentrationsn the snowpack at NM (reflectingsalty drift

snow advection rom the upwind Atka Bay) and in surfacesnowat DDU aswell as the high temporal variability ndicated

in Table 3 by the arithmetic mean to median ratio. The geo-metric standard deviation of the raw sea-salt data are 2.5 at

NM and DDU and 3.5 at HB which translates o a rather high

episodicity, howing hat roughly 10% of the highestconcen-

trationsexplainas much as 30% of the total sampledsea-saltatNM and DDU and even 50% at HB. There is no surprisetherefore that generalcirculationmodels ailed to simulate he

present mean sea-salt concentration and its seasonalcyclewithin the coastalAntarctic boundary ayer [Genthon,1992].At least, where sea-salt ecords are available n daily resolu-

tion, local and large scale effects might be disentangled

throughsynoptic nalyses. he comparability etweensiteswillremain weak, however, until the sampling procedures are

Table 3. DescriptiveStatisticsof 10 Day Mean AtmosphericSea-Salt Concentrations

Dumont d'Urville a

Jan. 1991 to Dec. 1995HalleyBay

Feb. 1991 to Feb. 1993Neumayera

March 1983 to Jan. 1996

Annual Annual Annual

Mean Summer Winter Mean Summer Winter Mean Summer Winter

n 146 36 33 71 16 18 431 100 112

Arithmetic mean 1360 2100 1060 200 160 330 860 580 910

s.d. 1000 1570 440 180 140 240 780 570 660

25%quartile 790 900 810 70 40 150 340 230 470Median 1060 1750 990 140 70 240 630 350 690

75%quartile 1600 2730 1300 260 290 490 1100 700 720Mean/Median 1.28 1.20 1.07 1.43 2.29 1.38 1.37 1.66 1.32

Sea-saltoncentrationsre n ngm 3. Summerefers o November-April, inter efers o May-October, denotes umber f datavalues,and s.d. is arithmetic standard deviation.

aCalculated from Na+.

bCalculated from C1-.




IO

Firn Core

HB

o 1.0-_

0.5-_

0.0

I

DDU

NM

Jan Apr Jul Okt Jan Apr

Mean annual sea-saltcycle at Halley Bay (HB),igure 3.Dumont D'Urville (DDU), and Neumayer NM) displayed smonthly means and normalized to grand averageconcentra-tionsover the observational eriodsshown n Figure 2 (exceptfor Neumayer epresentinghe period 1983-1995). n the toppanel he normalizedmeansea-salt ycleobserved ver he ast25 years n the firn core D 235 of the easternRonne Ice Shelf[Minikin, 1994] s shown or comparison.

clearlycharacterized nd homogenized.n this context,a well-defined dissectionnto a large and small sea-saltparticle frac-

tion by cyclon or (virtual) impactor stagesmay be recom-mended n future campaigns.Quantificationof the large sea-salt fraction during snow drift episodes will remaintroublesome,however,due to its size distributionpartly over-

lappingwith the size of blowingsnowcrystals.

3.2. Seasonal Cycle

As shown n Figure 3, the mean annualsea-salt ycleseenatall three stations s relativelyweak, if the distinctsummerpeak

at DDU arising rom local seaspray s disregarded. he annual

sea-saltmaximumat HB and NM occursduring he winter half

year which is also observed n the atmospheric ecords atMawson Prosperot al., 1991] and SouthPole [Bodhaine t al.,

1986], as well as in almost all seasonally esolved irn cores[Mulvaney nd Peel, 1988;Mosley-Thompsont al., 1991;Mini-kin et al., 1994; Wagenbach t al., 1994]. No seasonalcycleswere reported,however, or Palmer and Marsh [Savoie t al.,

1993] ying ar north close o the tip of the Antarctic Peninsula.For the mid to high latitude southernhemisphere, ricksonetal., [1986] predict from analyses f wind speed distributionsalso a rather low winter to summer ratio in the sea-saltpro-

ductionrate (less han two between he midwinter and mid-summerperiods). The seasonalpattern at HB and NM ismainly driven by the low concentration evelsduring the sum-

mer monthswhich may be underestimated n the HB data by

roughlya factor of 1.4 sinceseasaltwascalculated ia C1- (seeC1- losses iscussedn section4). Comparing he mean arith-

metic sea-salt oncentration f the midsummer D, J, F) withthe midwinter months (J, J, A) given in Table 3, winter tosummer atiosof 1.6 at NM and up to 2 at HB are obtained.Afurther difference between the midsummer and midwinter sea-

salt situation s clearly seen at all three stations n the higher

variability of the 10 day means (expressed s the mean to

medianratio in Table 3) duringsummer.This seasonal iffer-ence may reflect the proximity of open water during summermaking it easier to produce extreme sea-salt peaks duringfavorablehighwind speedepisodes. n the basisof the stationclimatologies escribed y K6nig-Langlo t al. [this ssue] hereis no substantialchange n the surfacewind regime over the

year at all three stationsand only a slight tendency or lower

meanwind speeds o occurat HB and NM betweenDecemberand February. Such a weak decrease n the storm activity

during these months may not explain, however, the relativesea-saltminimum n the annualcycle egularlyappearingdur-ing the open water seasonat NM, HB, and Mawson. Hence,except for the peculiar situation of DDU, the proximity ofopen seawaterareasduring summer s not seen n the atmo-

spheric sea-salt ecordsnor in firn cores of coastalregions.This posesquestionsabout the sea-saltsource,responsibleduring he winter seasonsor short erm (1-2 day) peaks eg-

--3

ularly seen at HB and DDU in the range of some •g malthough he sea ce coverageswell developed. hesesources,finally leading to winter sea-salt maximum concentrations,

would have o overcompensatehe reducedoffshoreopenwa-ter area,aswell asparticle emovalduring ongrange ransportover he sea ce. The followingpotentialsourcesor the wintersea salt may be considered:

1. Coastalpolynyasransiently penedby strongwindsandocean currentsmay provide a local source,which, however,

cannotexplain he hugepeaksseen n winter snow ayerseven500 km southor at elevations round 1000 m asl (seeTable 2

and references herein).2. Leads responsible or an open water fraction in the

winter sea ice cover n the range of up to some 10% should

show a much weaker specificparticle productionrate due tothe reduced wind fetch over water. On the other hand, an

increasedproduction of spume drops may be expected romthe surf zones prevailing at the rim of leads and ice floes

alreadyunder moderatewind speeds.3. Putting he major sea-saltsourceduringwinter north of

the sea ce edgewould require a much more efficientmeridi-onal transport in the surface layer or an unrealistically n-

creasedproduction ate by bubble bursting.The scale ength




for sea-salt article emovaldetermined yMinikin et al. [1994]over 600 km on the Ronne ce shelf s around30% per 100 km

(same or winter and summer)which can be regardedas alower limit, due to much lower precipitation here. Accord-ingly, the depletion n the atmospheric ea-salt oad during a1000 km transportover (source ree) sea ce would be largerthan a factor of 20.

In anycase,a dominating ea-salt ourcenorth of the actual

sea ice edge would suggest hat the observedsea-salt evelshould ary broadly n antiphasewith the sea ce extentwhichis clearly n contradiction o what is observed n aerosolsam-plesand ce corerecords. n conclusion,t appears hat noneofthe openwater sea-salt ources ddressed ere may explain hemagnitudeand seasonal ariability n the winter sea-salt oadseen at the higher atitudesof coastalAntarctica.

4. Chemical Sea-Salt Fractionation

Enrichmentsf SO42- r depletionsf halogensith espectto seawater n marine bulk aerosolare common phenomenaarisingat remote marine sites rom additional biogenicnon-

sea-saltNSS)SO24contributionsnd rom eaction f otheracidicspecies MSA, HNO3, N205) with the alkaline sea-saltpattioleg re. nectivelvParun•nat al__1986] During summermonths hugeSO42- urplusnda clearC1- deficitwas ndeedobservedat all three stationsdue to the relatively high atmo-

spheric oad of biogenicsulphur Minikin et al., this ssue]andNO•- [Wagenbach t al., this issue]during that season.How-ever,duringwintera significantO42- eficit as previouslyreported from NM [Wagenbach t al., 1988] and a slight C1-

surplusrelative o Na+) wasevident t all threestations. osuch ystematicepletion f SO42-n bulkaerosol amplesasreported from remote marine sitesoutside he Antarctic re-gion. In the following section, he emphasiswill be on the

SO42- epletion henomenonnd tsunderlyingrocesses.

4.1. Chloride Depletion

Acid-induced C1- mobilization may occur from airborne

sea-saltparticlesor (as a samplingartifact) from sea-saltal-readyaccumulated n the filter surface.During the major C1-depletionperiod December to February the typical depletionof the C1- to Na+ ratioswith respecto BSW are a factorof 2.3at NM, 1.1-1.5 at DDU and ---1.4 at HB. The relatively high

NM valuepossibly rises rom the much ongercollection ime

(1-2 weeks),whereasat DDU, C1- mobilization s much esslikely (although eflon iltersare used)due to the highsummersea-salt evel and the occurrenceof summer NH 3 concentra-

tionsof up to 5/zg m 3 observedyLegrand t al. [this ssue]via (double)mistchamber amplings.he C1- depletionat HB

is highly ncertain ue o the ackof sufficient a + data.Sincegenerallyno major problem arises n calculating he sea-saltcontributionn coastal reasvia Na+, C1- depletions re notfurther discussed here.

4.2. Sulphate Depletion

A significant O42-depletion, ecognizedrom negativeNSS-SO42- oncentrations, as first reportedby Gjessing[1984] or firn samples rom near the ice edge and by Wagen-bachet al. [1988] at NM for winter bulk aerosol.As illustrated

in Figure4, the negative SS-SO42-alues ound n winteraerosol at NM, HB, and DDU cannot be explainedby theoverall nalyticalncertaintyn the calculationf NSS-SO42-:the sea-salt O42-raction s not so highas to precludehe

100

2O

i

'

:

- :::

-

,

•///,4d,'• DDU

• NM

• HB

I I I IIIIIJ I I I IllIll I I I IllIll I I I IIIIII I I l iillj I f I l itlij I ] I [Jill I [ I [ l iill

I 10 100 1000 10000

seasalt ng n-3

Figure 4. Expected elationshipbetween he relative uncer-taintyR (lo9 in theNSS-SO24calculationf Antarctic interaerosol samplesas a function of sea-saltconcentration.Pureanalyticaluncertainties f 10% (solid line) and 5% (dashedline) are assumedwhich are taken independentof the concen-tration evels nd denticalor SO42- ndNa+ (C1-) analyses.The realNSS-SO42-interbackgroundevelwas ixed t 20 ngm -3. The observed raw winter sea-salt data at Dumont

d'Urville (DDU), Neumayer NM), and Halley (HB) are dis-played n the lower panelby bars:25% quartile left margin),median (centralmark), and 75% quartile (right margin).Al-most all data are well below the 100% uncertainty limit inquantifying SS-SO42-interaerosol oncentrations.

calculationof a meaningfuldifferencebetween total and sea-salt SO42-f a realisticower imit of the background SS-SO42-evelaround 0 ng m 3 [Minikin t al., this ssue]s

assumed.Such analytical imitations are commonlyencoun-tered, however,duringwinter at islandpositions n the south-ern midlatitudes Ayers nd Ramsdale,1988],but possibly lso

--3

at Marsh Stationwhere seasalt may be higher han 20/•g m[Savoieet al., 1993].

As illustrated n Figure 5, dependingon the individualsea-saltcontribution,henegative SS-SO42- ay each alues pto 200ngm-3 in NM aerosol ndup to some 00ngg- • in afirn core from the Ronne Ice Shelf. Similar figures are ob-tained from DDU and HB aerosol samplesas well as from

fresh snowat HB and NM. This "apparent fractionation"of

sea-salt O42- etween eawaterndairborne articleseadsoa systematic nderestimation f the mean annualatmosphericNSS-SO42-enerally ot much arger han 10%. t may ead,

however, ven o negative rand verage SS-SO24valuesnice coresdrilled relativelynear the coast e.g., Berkner sland,North Dome [Wagenbach t al., 1994]). Furthermore, seriousmisinterpretationf theMSA to NSS-SO42-atio Wagenbach,1996;Legrandand Pasteur, his ssue]aswell as of an eventualanticorrelationetweenNSS-SO42-ndseasalt n coastalcecore records Wagenbach t al., 1994] may be expectedby thisphenomenon.or example, O42- epletionwasnot consid-ered by Savoieet al. [1993] in evaluating heir aerosol data,whiched o erroneouslyighMSA to NSS-SO42-atios uringwinter. Peeland Mulvaney 1992] nterpreted he clear negativecorrelationhey foundbetweenNSS-SO42-nd C1- in theDollemancecore n terms f climatic hangeslthough O42-depletionmight havecontributedsubstantiallyo the observed



10,968 WAGENBACH ET AL.' SEA-SALT AEROSOL IN COASTAL ANTARCTIC REGIONS

a)

3O0

ß

.****

-300

-600

0.00

ß

ß

ß ß

ß

o ß

ß ß

ß ß ß ß Summer aerosol

ß o Winter aerosol

'..o

, I

! , , , , i , , , , i , , , , ! ,

0.50 1.00 1.50 2.00

Na+ IJgm'3

b)

600

300

-300

ß Summer snow

o Winter snow

ßß

ß ß

ßß

ß

ß .... ß ................................................................

ßß

-600

O.O0 O.50 1. O0 1.50 2. O0 2.50 3. O0 3.50 4.00 4.50

cr [pgg-•]

Figure5. (a) Scatterplotf NSS-SO42-calculatedia the BSW atio)versus a+ for the complete,awaerosoldata set at Neumayer. b) Sameas Figure5a, but for shallow irn core data used n Figure3 and C1-as BSW referencespecies. inear regressionines refer to winter data (associated ith the May-Septemberperiod for the aerosoldate and with approximatelyhe midwinterseasonor the firn core date).

coupling. An attempt is needed therefore to get at least afirst-order orrectionor NSS-SO42-hich s normally alcu-lated via:

[NSS - SO4-]: [SO42-]total-[x]

with x denoting he ionic seawater eference species e.g.,

Na+) andk = [SO42-]/[x] enotingherespectiveulksea-water (BSW) ratio. As alreadyapplied or firn coresof the

Weddell SearegionbyMinikin et al. [1994]and or NM aerosol




data by Wagenbach1996], a formal downwardcorrectionof k

maybe achievedy inear egressionf the winterNSS-SO42-dataversus a+ (alternatively 1-) or, lesssimple ndgivingthe maximum orrection, y determining he lower envelopeof

the wholedata set.Adding he obtained negative) lope o theconventionalvalue i.e.,0.25 n the case = Na+) giveshecorrectedmeank valuek' (k' -< k) associated ith airborne

sea-salt articles.For the NM aerosolexampleshown n Figure5 the slope is -0.175, and the mass ratio k' becomes0.075

(instead f 0.25)whichcorrespondso a dramatic O42- e-pletion actorf (definedasf - k/k') betweensea-salt articles

and bulk seawaterof 3.3. In the caseof the firn core example(basedon C1-) of Figure 5, f is found to be 5.5.

Alternatively, ' may be obtainedby requiring hat the cor-relationbetweenwinterNSS-SO andNa+ (or C1-) becomesa minimumwhich s a reasonable ssumption t coastalsitesatleast for high sea-saltconcentrations. his procedure clearlyillustratinghe artificial oupling etween SS-SO42-ndsea-salt species) an be applied even to more scattereddata setsand may be used o check he regressionesults. n the caseofthe aerosoland firn core data alreadyprocessed bove, be-

comes4.1 and 5.3, respectivelysee Figure 6). Regarding herelatively arge scatter or low concentration alues,both meth-

odsare very sensitiveo the mostnegativeNSS-SO4- datapoints generallyassociatedwith high sea-saltconcentrationsand tend to give an overestimated ractionation actor. Also,

further shortcomingsde-emphasizinghe need for a formallyhighaccuracy f k') are that the procedures till rely on a moreor lesssubjectivedata dissectionnto summer and winter val-

uesand that it is a priori unknown or what seasonshe derivedk' are truly representative. ome hints on the seasonal ccur-

renceof artificiallyeduced SS-SO42-aluesconservativelydefined sbeing ower han10ngm 3) at each tationmaybedrawn from Figure 7, however.At all stations,maximum fre-

quenciesn the occurrencef underestimatedSS-SO42-on-

sistentlyemerge during midwinter.As illustrated n Figure 7,the levelingoff of depletion requency oward the equinox sambiguous ue to a steady ncrease f biogenicNSS-SO42-during that period.

To provide common ase n calculating SS-SO4- con-centration within this special JGR section, he most simpleregressionmethod was individually applied for each year'saerosol data sets, defining the winter subsamples s June toAugustor, instead,June to September.Surfacesnowsamplestaken at HB and DDU in high temporal resolutionare pro-cesseddentically.Excluding he September1991 data already

affected y volcanic O4- from Mount CerroHudson M.Legrand,personal ommunication, 997) and 2 yearswith cor-

relationcoefficients elow0.5, the grandaverage ' (referring

to Na+) for aerosol nd reshsnow ecomes lose o 0.07.Noattemptswere made at this stage o define seasonally djustedk' values, ence ' = 0.07 correspondingo thesea-salt O4-to Na+ mass atio in bulk referencesea-saltparticleswasnormallyapplied n the respective apers or aerosolaswell asfor snowsamples hroughoutall seasons.

The SO4- depletionactor derived y heabove rocedureappears o be almost ndependentof the site specific ea-saltlevel. The value of f is virtually the same for NM and HB

aerosolsamples 4.1 and 3.6, respectively) ut is significantlylower at DDU (2.6): there is also no obviousdifference n fbetween aerosoland fresh snow at each site which suggeststhat f is not very sensitive o the particle size fraction consid-

ered. Available values rom 11 highresolution irn cores rom

0.80

0.40

0.00

0.00 I O.0 0.20 025k' k (S042'/N•1) ISW

b) r 1.00•

0.50

0.00/ , , ] , ,, .....0.00 I 0.05

!

k' k S042'/01) 0.10 014SW

Figure 6. Correlation oefficient betweenNSS-SO4- andthe seawater eference speciesconcentrationversus he sea-water eferenceatiok used o calculatehe NSS-SO42-alues

with k' indicating he absoluteminimum of r: (a) for Neu-mayer winter aerosoldata shown n Figure 5 with Na + asseawater eference species nd (b) for firn core winter datashown n Figure 5 with C1- as reference species.

the Weddell Sea sector angebetween6.7 and 3.8 (mean 5 ___0.9) in the region up to 600 km inland on the easternRonneIce Shelf [Minikin, 1994] with no obvious elation to the ice

edge distances nd with similar valuesalso at higher eleva-tionsof Berkner sland. nterestingly, irn coresanalyzedsouthof NM showa decreasingrend with f close o 3 and 2.5 at 70and 160 km distance rom NM, respectively, own to 1.4 at theRitscherHochland 1000 m asl,distance 00 km) [Moser,1991;

Trefzer,1992].The reason or this pattern is not clear yet, butmight be connected o the difference n the sea ce cycleat this

sector f compared o the Weddell Sea region (see followingsection).

4.3. Sulphate Fractionation Process

Gjessing 1989] suggestedeemissionof (NH4)2SO4, rac-tionationduring og formation., swell as ractionation uringfreezing of airborne seawaterdroplets as possible easons or

the extremely egative SS-SO42-oncentrationse found ncoastal firn. The clear evidence that bulk aerosol is also de-

pleted n seawater O4- makes nlyhis attersuggestionikely.Indeed,SO4- fractionationuringreezing f seawaterice) sa well known process Richardson, 976] which is basically




a)

(D

O"

(D

.>

(D

60

40

20

0

Jan

--o--eumayer /=\ /q\.-o- HalleyBay , , /,•,

- • Dumont'Urville•,,/ V• "•,?' o" ,' ',\

/ ,! ',ß

, /

'\

Feb Mar Apr Mai Jun Jul Aug Sep Oct Nov Dec

b)

3.0

2.5

m 2.0

Eo

o

i

03 1.0

Z

0.5

0.0

\ / \ • Neumayer\ / ,

c:!X\' \, - '•-' Halleyay

,/•_ \,\ - -•-Dumont'Urville

Jan Feb Mar Apr Mai Jun Jul Aug Sep Oct Nov Dec

Figure . (a)Relativerequencyor hemonthlyccurrencefseawaterO42-epletionsnaerosolamplesversus easons.or all three stations, SS-SO42-alues alculatedia the BSW ratio are assumedo beaffectedy sea-saltO•- depletionf theyare owerhan10 ngm 3. (b) Annual yclesf NSS-SO42-calculatedia the corrected O42-o Na+ mass atio n bulk eference easaltof 0.07andnormalizedo therespectiverand verageshowno indicateheNSS-SO42-ncreaseoward quinox).

drivenby the crystallizationf Na2SO ß 10H20 (mirabilite)already ccurring t temperatureselow 8.2øC. Since he saltcrystals re associatedith the ce attice, he remaining rinestarts o get ncreasinglyepletedn SO42-and o a muchlesser xtent n Na+) on progressiveooling elow hiscriticaltemperature.ome onnectionf theSO42-ractionationithcold air temperaturess to be expectedrom the missing e-

pletioneffectat temperatemarinesites.Again, n the coastalhighArcticwhich s subjecto hugecontaminationy anthro-pogenicO42- uring interBartie,986], ea-saltO42- ef-icitswould not be immediately ecognized.

In a seriesof laboratory xperiments,ea-salt articleswereproduced,herefore fromclean,deepAtlantic)seawater am-ples,under air temperature onditions own o -28øC at-




1.70

1.60 - o

o1.50 - o o

o

1.40 - ½oo oo o

o

1.30 o o' 0 0 _,,., O0 0 0O O(7• '"O O 0'• oO

1.20 oøo,,•_•n• • • o _ o oo• •n•- o 0• • O• o o o•o _o•-• o•Ooo•o•• • a o- eø o

BSW--1.00oo• •• • o c

0.90+ o

o i ooo.70 .... o I .... / .... I ....0.00 0.50 1.00 1.50 2.00

I f-1S042-)SW

Figure 8. Theoreticalinear elationshipetweenhe Na+ depletionactor (Na+) (withrespecto C1-)and he eciprocalO42- epletionactor- • (SO42-)with especto Na+) n seawaterf mirabiliteNa2SOß10H20 ) is progressivelyrecipitated nd nstantaneouslyemoved straight ine). For definitionof depletionfactors see ext. Data points efer to raw winter aerosolvalues rom Halley Bay (HB), Dumont D'Urville(DDU), andNeumayerNM) with Na+ > 300 ng m 3 (in order o minimizehe effect romunknownNSS-SO42-ontributionsot consideredere) and o C1- to Na+ mass atiosbetween and0.5 to takeaccountof analyticaloutlyers.

annual sea ice and air temperature cycles s thus expected oconfine he most probableoccurrenceof surfacebrine forma-

tions o the winter half year (see alsoFigure 7). It is expectedthereforehat the SO42- epletionactors erived bove re

not commonly pplicable or the open water season i.e., midto late summerdepending n the positionof the station).ThismayexplainherelativelyowSO42- epletionactor in aero-sol and surfacesnowat DDU where the openwater seasonslongerand the mean sea ce coverage s smaller f compared o

the otherstations. pplyinghe SO42-o Na+ referenceatioof 0.07 also or DDU midsummer amplesgenerally nhancedin seasalt) was ound by Minikin et al. [this ssue] o lead to a20% overestimationf NSS-SO42-.hey assumedhereforethat no significantO42-raction ccurs t DDU during hatseason.As addressedabove, also values n ice cores of the

Weddell Sea sectorwhere ice coverage s more persistentap-pear to be enhancedover their counterparts rom the more

easterly ositionn theAtlantic ector. o SO42- erosol ataare presented y Savoie t al. [1993] rom Marsh (62øS),whichamong he sites n question s least influencedby sea ce andwhere extremely high sea-salt concentrationsprevail year-

round.nspectionf theNSS-SO42-atapointsheypresentedfor Palmer (65øS) evealed,however,only relatively ew neg-ative alues espite ratherhighsea-saltevel 3900ngm-3).Accordingly, or a givensite at the coast,seasonally djustedvaluesneed to be established,or example,by consideringhesitespecific emperatureand sea ce climatology f the summer

half year. The assumption,ot confirmed et, that sea ce brineprovideshe SO42-ractionatedarticles uggestshat sea ceconstitutes he major sea-saltsource or high latitude coastalAntarctica. This is because n that region almost all aerosolsamplesor ice core horizons esponsibleor the regularlyoc-

curring annual sea-saltmaximum n winter appear to be sig-nificantly epletedn sea-salt O42-.

5. ConclusionsAtmosphericsea-salt oads at coastalAntarctic sites are

characterized y an extremely arge short ime variabilityoverall seasons nd significantlyower concentrations t the Wed-dell Sea coast.The mean annual concentrations ppear o bestrongly nfluencedby site specificaspects. his includes hesampling ite positionwith respect o the coastline nd surfacewind pattern, but also nonuniform samplingstrategiesandtechniques.More effort is certainlyneeded here to achieveabetter defined arge particle sampling n order to improve hecomparabilityof the results. Consequently, he site specificobservations vailableare generallyof questionable alidity n

givinga representative icture or a generaluse (e.g., n gen-eral circulationmodel (GCM) validations).

The main featurescommon o all recordsat higher coastalAntarctic latitudes include, first, no echo of the seasonalsea ce

cycle e.g.,of the respective ffshoreopenwater raction).Thisis shownby the fact that (with one peculiarexception)at allsites he lowest sea-salt evel occursduring summer. Conse-quently, he major source ssociated ith strongwinter sea-saltpeaksappears o be not simply elated to the commonbubbleburstingprocess peratingat openwater areas.A second om-

mon eatures a systematic,trong, epletion f sea-salt O42-in aerosoland snowsamples f the winter seasons ompared obulk seawater.Here major unknowns till existwith respect othe seasonal s well as to the spatial occurrence f this phe-nomenon.

The latter finding,persistentlygnored n most of the previ-




ousglacio-chemical tudies n coastal egions,deservesurtherattentionn order o obtain eliablewinterNSS-SO42-alues.Thusevaluationsf biogenic O42-ce core ecordsmaybesignificantlymproved: n particularconcerningheir quantita-tive relationship o MSA as well as their (possible) ntimateconnectiono sea-salt ecords hrough he spatio-temporal eaice variability.

Although irst aboratoryexperiments uggesthat brine su-perimposedn sea ce is depletedn SO42- nd thusmayconstitute the hidden source for winter sea-salt aerosol, field

experiments re still urgentlyneeded o identify he controllingmobilizationprocesso get the brine airborne.Confirmationofthe proposedole of sea ce brine n the observed O42-rac-tionationwould make the sea ce cover he dominatingsea-saltsource at least) with respect o coastalAntarctic snow ields

with far reaching implications or the interpretation of the

respectiveong term ice core records.

Acknowledgments.We thank the overwintering rewsat DumontD'Urville, Halley, and Neumayer or carefulsamplecollections swellas U. Trefzer and E. Lehrer for analyzingpart of the Neumayersamples nd for their encouragementn data editing, and E. Pasteurand N. Holman for analyzing omeof the Halley snowsamples. hework was partly funded by the German ScienceFoundation DFG)and by specialgrantsof the Alfred-Wegener Institute for Polar andMarine Research Bremerhaven) o the Institut ffir Umweltphysik swell asby the EuropeanCommunitySTEP programwithin the project,Polar AtmosphericChemistry.

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(ReceivedMarch 24, 1997; evised une 12, 1997;accepted une 18, 1997.)

1998 - Sea Salt Aerosol in Coastal Antartic Regions

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