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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]
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