The First Greenland Ice Core Record of Methanesulfonate and Sulfate Over

GEOPHYSICALRN•BARCH LETTERS, VOL. 20, NO. 12, PAGES 1163-1166,/UNE 18, 1993

THE FIRSTGREENLAND ICE CORERECORD OF METHANESULFONATE AND SULFATE OVER A FULL GLACIAL CYCLE

MargaretaE. Hansson

DepartmentofMeteorology, Stockholm University

Eric S. Saltzman

RosenstielSchool of Marine and Atmospheric Science, University ofMiami

Abstract.Methanesulfonate (MSA) in ice coreshas Greenlandice sheet.The altitudeof 2,340 m a.s.1.minimizes attractedattention as a possibletracer of pastoceanic the local marineinfluence. The Renlandice coreis only 324 emissionsof dimethylsu!fide(DMS). After sulfateMSA is m long.The record of theglacial period and the previous thesecond most prevalent aerosol oxidation product of interglacialis compressedinto the deepest20 m, but is well DMS,but in contrastto sulfate,DMS oxidationis theonly preserved[Johnsen et al., 1992b]. knownsource of MSA. The hypothesisby Charlsonet al., The ice core was cut with a stainless steel microtome knife [1987]of a climatefeedback mechanism with sulfur underclean room (class 100) conditionsinto 5 cm samples emissionsf¾om marine phytoplankton influencing the cloud asfollows: 55 continuoussamples were cut between86 and albedoadds to the interestin establishinglong records of 89 m depthrepresenting the time period^.D. 1812-1820and MSAand non-seasalt sulfate spanning large climatic 374 continuoussamples were cut in the deepest20 m of the changes.Records of MSA andnon-seasalt sulfate covering ice corerepresenting approximately 10-145 ka B.P.[Johnsen timeperiods from a few yearsto thousandsof yearhave andDansgaard, 1992]. The sampleswere analyzed by beenextracted from antarcticice cores[Ivey et al., 1986; chemicallysuppressed ion chromatography.Major anions Saigneand Legrand, 1987; Legrand and Feniet-Saigne, 1991' (CI',NO3', SO42') and cations (Na +, NH4+, K+, Mg2+, Ca 2+) Mulvaneyet al., 1992] but onlythe recordfrom the Vostok weredetermined on an integratedDionex (4000i/2000i) icecore [Legrand et al., 1991] coversa fhll glacialcycle. systemusing AGSA/AS5ASg and CationfastsepVII The concentrations of MSA and non-seasalt sulfate in columns,respectively. MSA wasdetermined in the same Antarcticahave been found to increaseunder glacial samplesbut on an othersystem using AG4/AS4 columns. conditions.Here we presentthe first NorthernHemisphere The uncertaintyin the analyses(! sigma)are estimatedat recordof MSA, and the first continuousrecord of non- lessthan +_10% for all majorions and +_30% for MSA. The seasaltsulfate, both extractedfrom the Renlandice core, seasaltcomponent of the sulfate(based on sodium)is on EastGreenland. The recordsare extendingfrom the average10% of the totalsulfate. Holoceneto the Eem interglacial!30,000 yearsB.P. The contrastto the SouthernHemisphere records is striking,with Result and discussion a decreasingconcentration of MSA with theadvance of glaciationbut an increasingconcentration of non-seasalt Theprofiles of MSA andnon-seasalt (nss) su!fate for the sulfate.A stronglinear relationship is foundin theRenland period10 to 145ka B.P.are shown in Figure1. Mean values ice core between the ratio of MSA to non-seasalt sulfate and for the climaticstages (i.e. conventionalmarine oxygen thetemperature, with higherratios associated with warmer isotopestages) are presentedin Table l. The MSA climaticstages, while the oppositerelationship to concentrationis a factorof 2.0-2.5 lower duringglacial temperatureis foundin the Vostokice core.A more maximum(stage 2) thanin interglacialperiods (.stage 5e and complicatedpicture is emergingof theuse of MSA in ice stage1, thelatter represented by two limitedsample series in coresas a quantitativetracer which suggests that previous Pre-borealand late Holocene).Preliminary results from the interpretationscan have been overly simplistic. GISP2 ice core (ongoing deep drilling in theGreenland Summitarea) support the glacial/interglacialMSA trend Samplingand measurements observedat Renland,suggesting that it is characteristicof the main Greenland ice sheet. The nss sulfate concentration TheRen!and ice core [Johnsen et al., 1992a]is the third is a factorof 1.9-2.7higher during glacial maximum in the surface-to-bedrockice core drilled on Greenland. It was samecomparison as above. This increasein nsssulfate recoveredfrom a smallisolated ice cap, only a fewhundred concentrationduring the glacialperiod has previously been metersthick on a highelevation plateau in Scoresbysund observedin boththe Dye 3 andCamp Centurydeep ice cores Fjord,East Greenland (71.2øN, 26.4øW), during a joint [Herronand Langway, Jr., 1985]. Nordicproject in 1988,The drill site conditions (e.g.- 18øC The molarratio (R) of MSA to nsssulfate in the Renland inmean annual temperature and 50 cmof iceper year in ice coreis stronglyrelated to the climate.The oxygen meanannual accumulation rate) are similar to thoseon the isotoperatio (•5180) indicates the past climate (by a linear relationshipto the localmean annual temperature Copyright1993 by theAmerican Geophysical Union. [Dansgaardeta!., 1973]) with low 15•80 values associated with low temperatures.When the dataare averaged over Papernumber 93GL00910 differentclimatic stages, them is a stronglinear relationship 0094-8534/93/93GL-00910503.00 (r2=0.99)between R andthe oxygen isotope ratio 3180

1163 1164 Hanssonand Saltzman: MSA and sulfate in Greenland ice

fromlaboratory oxidation studies [Hynes et al., 1986]of the reactionof DMS with OH. This lattertemperature dependenceis thought to be responsiblefor theobserved [Bateset al., 1992a]latitudinal gradient of R, w/thhigher R- valuesfound at higherlatitudes. The existenceof other factorscontrolling R apartfrom temperature.(e.g. seasonal transportdifferences, additional sources of nsssulfate) is indicatedby theannual cycle of R measured[Ayers et al., 1991]at CapeGrim, Tasmania, where R decreasesduring winter.Undoubtedly, the R for differentglacial stages obtainedat a singlesite of depositioncan be influenced by severalprocesses. In an interglacialclimate, the marinebiogenic sulfur compoundsin Greenlandprecipitation can come from either regionalsources (i.e. Greenlandcoastal waters) or more distant,lower latitude sources. Trajectory analyses of air massesinfluencing the South Greenland ice sheet[Davidson • 100 et al., 1993a]indicate that the influenceof differentsource areasvaries with season,favouring the regional sources duringsummer. In contrast,the regionalsources are closed off in a glacialclimate due to the seaice cover.

50i,. Palaeooceanographicreconstructions [Ruddiman and 01 , Mcintyre,1981 ] placethe winter sea ice extentas far south 0' ' 20' ' 4'0'' '6'0'' '8'0'' '100'' '120'' '•40 as45'•N during the most advanced glacial stage. Time(ka B.P.) The interglacialR-values (Table 1) foundat Renlandare Figure1. Top:The Renland 15180 profile as 10 point running lowerthan R expectedfor the regionalmarine boundary averagesof 2.5 cm samples.The differentclimatic stages are layer.Recent time seriesmeasurements in Mace Head, indicated.The arrowindicates the positionof the boudinage Ireland,show summertime R-values of 0.30 (D. Savoieet al., layer.Mid section:Methanesulfonate (MSA) as 5 point manuscriptin preparation)suggesting that pre-industrialR runningaverages of 5 cm samplesin an envelopeof for the marineboundary layer around Greenland should be at calculated standard error of mean. The mean value over leastas high. The glacial R-values are lower than R presently sevenfull yearsof accumulation(^,D, 1813-1819)is measured,on average0.065 [Savoieand Prospero, 1989], in indicatedby a cross(+_ s.c.). Bottom: non-seasalt (nss) sulfate low andmid latitudes.This may indicate the importance of presentedas for MSA. The seasaltcontribution has not been sulfateof otherorigin in the Renlandprecipitation, such as extractedbeyond 120 kyr B.P.(dashed line) because of volcanicor othercontinentally derived sulfate. extremelyhigh sodium concentrations in some melt layers. Apportioningdifferent natural sources of non-seasalt sulfatein the precipitationof todayis difficult,and more so of thepast. At present,volcanic sulfur emissions from (Figure2), with higherR-values associated with warmer eruptiveand non-eruptive degassing volcanoes in the stages.R rangesfrom 0.077 in stage5e to 0.014in stage2. NorthernHemisphere (NH) haverecently been estimated Thisrelationship to temperatureis inverseto thetemperature [Bateset al., 1992b]to be of the sameorder as the biogenic dependenceof MSA productioninferred [Berresheim, 1987] emissions.Other significant non-anthropogenic sources of

TABLE 1. Mean concentrationsand standarddeviations of MSA and nsssulfate in the Renland ice core .... Stage DePth Time Numberof /5180 MSA nssSO4 2- Molar m ka B.P samples %0 ng/g ng/g ratio R

1' LateHolocene 86.60- 89.05 (A.D.1813-1819) 49 -27.5 3.0 + 1.5 50 _+331 0.060 1' Pre-boreal 305.80 - 306.55 10.0 - 10.5 15 -28.0 2.4 + 1.2 48 + 14 0.051 YoungerDryas - 307.30 - 11.8 15 -30.6 1.5+ 0.9 77 + 29 0.022 Aller6d-B611ing - 308.35 - 14.4 21 -29.0 1.7 + 0.9 50 + 15 0.036 2 - 311.75 - 30.2 67 -31.3 1.2 + 0.7 97 + 32 0.014 3 - 315.15 - 57.6 64 -30.2 1.5 + 0.8 61 + 24 0.026 4 - 319.85 - 70.0 16 -30.9 1.6 + 1.2 95 + 43 0.020 5a-d - 321.35 - 110.2 30 -29.0 2.0 + 1.3 54 + 21 0.040 5e - 323.05 - 121.6 33 -25.8 2.5 +_1.3 36 + 9 0.077 5e(melt layers) - 324.35 - 144.7 26 -24.4 3.7+ 1.6 (68+ 43)2

Boudinagelayer 3 315.65- 319.55 63.5- 64.5 77 -32.2 0.8 + 0.6 137 + 27 0.006 1. fivesamples influenced bythe volcano Tambora eruption excluded 2. sea salt contribution not extracted 3. dueto a pinch-and-swellinstability [Staffelbach et al., !988] Hanssonand Saltzman: MSA andsulfate in Greenlandice 1165

0.08- relationships[Legrand et al., 1992]are found in bothice coresbetween R andisotopic temperature but with opposite 0.07' signs.It showsthat R in polarprecipitation can not simply 0.06- bea functionof atmospherictemperatures. However, it ./•) LateHolocene wouldalso be remarkableif thestrong linear relationship to 0.05' temperatureinthe Renland ice core is causedby changing (l)Pre-boreal source strengths of two, or more, independent sources of 0.04' sulfur.

0.03' Conclusion

0.02- TheRen!and ice coredata suggests a glacial Arctic 0.01 atmosphericsulfur cycle influenced by low latitude oceanic •••in2age=, layer emissions,possibly decreased, and non-biogenic sources in 0 , f , -33 -32 -•1..... -•0 ..•O -l•8 '•.7 ' -"26 '25 contrastto Antarctica which appears dominated by increased 8480(%0) highlatitude oceanic emissions. The isotopictemperature profilessuggest a roughly parallel climatic development Figure2. Plotof themolar ratio (R) of methanesulfonateto [Johnsenetal., 1992a]in Greenlandand Antarctica which non-seasaltsulfate against 8180 as mean values for the callsin questionthe role of marinebiogenic sulfate in indicatedperiods (r2=0.99). climateforcing, or otherwiseits exclusivity among the atmosphericsulfate aerosols. However, it hasto bestressed sulfatehave yet to be found.Model studies [Langner, 1991] thatit isthe composition and size distribution of the total ofthe distribution of troposphericsulfate indicate the aerosolin theatmosphere that affects the direct radiation increasingimportance of volcanicsulfate with altitude, and balanceand the cloud albedo, why records of non-seasalt suggestthat volcanic sulfate may dominate the mid sulfatealone demand cautious use when discussing climate troposphereatmid and high latitudes in theNH undernon- forcing.The nss sulfate represents less than 5% of thetotal anthropogenicconditions. In theglacial period, the exposure aerosolmass in the Renlandice coreduring full glacial of continentalshelves due to the se.alevel dropand the conditions.In addition,the apparent influence from enhancedaridity on the continents may have added a changingclimatic conditions on the ratio R hasto bemore terrestrialsource of non-biogenicsulfate. High understoodbefore using MSA as a quantitativetracer over concentrations[Johnsen et al., 1992a]of calciumand longtime-scales with major climatic changes, either as insolubledust indicate an increasedtransport of continental indicatorof therelative strengths of biogenicversus non- materialto the Greenland ice sheet. The difference in nss biogenicsulfur sources or indicativeof changesin the calciumconcentration between interglacial and full glacial principlesource region. Further studies are necessary. totake conditionsis one order of magnitude.The correlation is high thefull advantageof thedetailed records that will be (r2=0.88)between nss sulf3.te and nss calcium in theglacial availablefrom the two deep ice coresdrilled on the period.This does not necessarily infer a commonsource Greenland Summit. sincea highcorrelation applies to severalions, but mayas wellindicate the importance of transformation,transport and depositionalprocesses. Acknowledgements.M.E.H. thanksthe colleagues at Thefactors controlling the distribution of sulfur GeophysicalInstitute, University of Copenhagen,for compoundsin polar ice are complex and can not be excellentco-operation and support within the Nordic unambiguouslyinterpreted in terms of sourceemissions or RenlandProject. Nordic Council of Ministersand Swedish atmosphericconcentrations. The relative contribution from NaturalScience Research Council are acknowledgedfor differentsources to theair massesinfluencing Greenland financialsupport. E.S.S. acknowledges National Science mayhave changed as a resultof differentatmospheric Foundationgrant DPP8822600. circulationpatterns [COHMAP members, 1988] in the glacialperiod. The precipitation rates at Renland during glacialstages decreased markedly (to a fifthof the present References valuein stage 2, 3 and4 [Johnsenand Dansgaard, 1992]) suchthat the contribution from dry deposition (presently Ayers,G.P., J.P. Ivey, and R.W. Gillett, Coherence between negligible[Davidson etal., 1993b])may have been seasonalcycles of d/methylsulphide, methanesuiphonate significantand at least in part responsible forthe increa, seof andsulphate in marineair, Nat. ure, 3..49, 404-406, 1991. nsssulfhte. However, the decrease of MSA andR can Bates,T.S., J.A. Calhoun, and P.K. Quinn,Variations in the perhapsbeexplained inthe context of three hypotheses: 1) methanesulfonateto sulfate molar ratio in submicrometer decreasinginput from oceanic DMS emissions, 2)a shift of marineaerosol particles over the SouthPacific Ocean, themarine biogenic sulfur source to regions where the J. Ge0Phvs.Res., 97, 9859-9865,1992a. conditionsgive lower initial R-values, and/or 3) changesin therelative removal rates of MSA andnss sulfate in the Bates,T.S., B.K. Lamb,A. Guenther,J. Dignon,and R.E. Stoiber,Sulfur emissions to the atmospherefrom natural glacialatmosphere. sources,J. Atmos.Che .m..., 1_.•4, 315-337, 1992b. 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