Archival of the water stable isotope signal in East Antarctic ice cores

33 Pages·2016·4.42 MB·English

TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
Archival of the water stable isotope signal in East Antarctic ice cores
MathieuCasado1,2,AmaelleLandais1,GhislainPicard3,ThomasMünch4,5,ThomasLaepple4,
BarbaraStenni6,GiulianoDreossi6,AlexeyEkaykin7,LaurentArnaud3,ChristopheGenthon3,
AlexandraTouzeau1,ValerieMasson-Delmotte1,andJeanJouzel1
1LaboratoiredesSciencesduClimatetdel’Environnement-IPSL,UMR8212,CEA-CNRS-UVSQ,GifsurYvette,France
2UniversitéGrenobleAlpes/CNRS,LIPHY,F-38000Grenoble,France
3UniversitéGrenobleAlpes/CNRS,LGGE,38400Grenoble,France
4AlfredWegenerInstituteHelmholtzCentreforPolarandMarineResearch,TelegrafenbergA43,14473Potsdam,Germany
5InstituteofPhysicsandAstronomy,UniversityofPotsdam,Karl-Liebknecht-Str.24/25,14476Potsdam,Germany
6DAIS,Ca’FoscariUniversityofVenice,Venice,Italy
7ArcticandAntarcticResearchInstitute,St.Petersburg,Russia
Correspondenceto:MathieuCasado([email protected])
Abstract.TheoldesticecorerecordsareobtainedfromtheEastAntarcticplateau.Waterstableisotopesrecordsarekeyfor
reconstructionsofpastclimaticconditionsbothovertheicesheetandattheevaporationsource.Theaccuracyofsuchclimate
reconstructions crucially depends on the knowledge of all the processes affecting the water vapour, precipitation and snow
isotopiccomposition.AtmosphericfractionationprocessesarewellunderstoodandcanbeintegratedinRayleighdistillation
5 andcomplexisotopeenabledclimatemodels.However,acomprehensivequantitativeunderstandingofprocessespotentially
alteringthesnowisotopiccompositionafterthedepositionisstillmissing,especiallyforexchangesbetweenvapourandsnow.
InlowaccumulationsitessuchasfoundontheEastAntarcticPlateau,thesepoorlyconstrainedprocessesareespeciallylikely
toplayasignificantrole.Thislimitstheinterpretationofisotopiccompositionfromicecorerecords,specificallyatshorttime
scales.
10
Here, we combine observations of isotopic composition in the vapour, the precipitation, the surface snow and the buried
snow from various sites of the East Antarctic Plateau. At the seasonal scale, we highlight a significant impact of metamor-
phismonsurfacesnowisotopicsignalcomparedtotheinitialprecipitationisotopicsignal.Inparticular,insummer,exchanges
of water molecules between vapour and snow are driven by the sublimation/condensation cycles at the diurnal scale. Using
15 highlyresolvedisotopiccompositionprofilesfrompitsinfiveEastAntarcticsites,weidentifyacommon20cmcyclewhich
cannotbeattributedtotheseasonalvariabilityofprecipitation.Altogether,thesmallerrangeofisotopiccompositionsobserved
intheburiedandinthesurfacesnowcomparedtotheprecipitation,andalsothereducedslopebetweensurfacesnowisotopic
compositionand temperaturecomparedto precipitation,constituteevidences ofpost-deposition processesaffectingthe vari-
abilityoftheisotopiccompositioninthesnowpack.Toreproducetheseprocessesinsnow-modelsiscrucialtounderstandthe
20 linkbetweensnowisotopiccompositionandclimaticconditionsandtoimprovetheinterpretationofisotopiccompositionasa
paleoclimateproxy.
1
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
1 Introduction
Ice is a natural archive of past climate variations. The chemical and physical compositions of the ice and of the air bubbles
trappedinsideareusedaspaleoclimateproxies(JouzelandMasson-Delmotte,2010).InGreenland,icecoresproviderecon-
structionsofpasttemperaturefromgreenhousegasconcentrationsandwaterisotopesbacktothelastinterglacialperiod,120
5 000yearsago(NorthGreenlandIceCoreProjectmembers,2004;NEEMcommunitymembers,2013).InAntarctica,lowac-
cumulationratesenablethereconstructionofpastclimateoverseveralinterglacialperiods,e.g.420000yearsatVostok(Petit
etal.,1999)and800000yearsatDomeC(EPICA,2004,2006).EventhoughreconstructionsfromicecoresfromGreenland
donotextendasfarbackasfromAntarctic’sicecores,highresolutionanalysesofthecoresfromGreenlandprovideveryfine
temporalresolutionandcanevenresolvetheseasonalcycle(Vintheretal.,2010).Seasonalvariationsarealsoimprintedinthe
10 snowisotopiccompositionofhighaccumulationsitesofcoastalareasofAntarctica(Morgan,1985;Masson-Delmotteetal.,
2003; Küttel et al., 2012). For low accumulation sites as found on the East Antarctic Plateau, there is no consensus whether
icecorerecordscanrevealtheclimaticsignalatresolutionsfinerthanmultidecadal(Baronietal.,2011)ornot(Ekaykinetal.,
2002;Poletal.,2014).Ekaykinetal.(2002)analysedmultiplepitsfromVostokandidentifiedlargespatio-temporalvariations
caused by post-deposition associated with surface topography and wind interactions. These non-climatic phenomena creates
15 highfrequencysignalinsinglecores,whichcallsforstackingisotopiccompositionprofilesfromseveralsnowpitstodistin-
guish the common climatic signal from this post-deposition noise. Still, on the East Antarctic Plateau, a significant seasonal
cycleisdepictedintheisotopiccompositionoftheprecipitation(FujitaandAbe,2006;Landaisetal.,2012;Stennietal.,2016)
andofthesurfacesnow(Touzeauetal.,2016).Sofar,whetherthisseasonalcycleisarchivedornotinburiedsnow,andthus,
whetherstackinganarrayofsnowpitspermitstoincreasethesignaltonoiseratioanddepictaclimaticrecordattheseasonal
20 scalefromwaterisotopicsignalremainunclear(Ekaykinetal.,2014;Altnauetal.,2015;Münchetal.,2016).
Severalstudieshavefocusedonunderstandinghowistheclimaticsignalarchivedintheisotopiccompositionofsnowand
iceontheEastAntarcticPlateau.SincetheearlyworksofDansgaard(1964)andLoriusetal.(1969),therelationshipbetween
iceisotopiccompositionandlocaltemperaturehasbeenattributedtothedistillationassociatedwiththesuccessivecondensa-
25 tioneventsonthepathfromtheinitialevaporationsitetothedepositionsite.Nevertheless,therelationshipbetweenisotopic
composition and surface temperature is not constant through time and space, due notably to processes within the boundary
layer (Krinner et al., 1997), the seasonality of the precipitation between glacial and interglacial periods (Sime et al., 2009),
variations in the air masses transport trajectories (Delaygue et al., 2000; Schlosser et al., 2004) and evaporation conditions
(Vimeuxetal.,1999).ForCentralEastAntarctica,theglacial-interglacialisotope-temperaturerelationshipappearsquiteclose
30 tothespatialgradient(Werneretal.,inprep),butitsvalidityforinter-annualvariations(Schmidtetal.,2007)andwarmerthan
present-dayconditions(Simeetal.,2009)ischallenged.
In addition, under the exceptionally cold and dry conditions of the East Antarctic drilling sites, the contribution of post-
deposition processes to the isotopic composition of the surface snow cannot be neglected (Town et al., 2008; Sokratov and
2
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
Golubev, 2009). It has been recently evidenced that summer exchanges between snow and water vapour at the surface sig-
nificantlyaffecttheisotopiccompositionofthesnowbothinGreenland(Steen-Larsenetal.,2014)andontheEastAntarctic
Plateau(Ritteretal.,2016).Inthefirsttopmetresofthesnowpack,isotopeexchangesinvolvedduringthesnowmetamorphism
andthediffusionwithintheporousmatrixadditionallyaffecttheisotopiccompositionofthesnow(Langway,1970;Johnsen,
5 1977;WhillansandGrootes,1985).Thediffusionlengthassociatedwiththeseprocessesdependsonthefirnventilation,the
snow density and the exchange rate between the atmospheric water vapour and the surface snow (Waddington et al., 2002;
SchneebeliandSokratov,2004;SokratovandGolubev,2009).Thiswiderangeofprocesseshamperstheinterpretationofthe
isotopicsignal,inparticularitisnotclearhowmuchoftheoriginalsignalacquiredduringtheformationoftheprecipitationis
conservedduringtheburialofthesnow.
10
Due to the extreme conditions on the East Antarctic Plateau, the general understanding of the processes involved in the
hydrological cycle (out of any isotopic consideration) is not straightforward, and there remains open questions such as the
definitionoftheaccumulation,theestimationofthemassbalanceortheimpactofsnowmetamorphismonthealbedofeed-
backloop.Inthecaseofaccumulation,thelowamountofprecipitation(Petitetal.,1982;Frezzottietal.,2007;Genthonetal.,
15 2015)andtheimportantcontributionofblowingsnowinthetotaldeposition(GrootZwaaftinketal.,2013;Picardetal.,2016a)
createspatchinessintheaccumulation,resultinginlargeuncertaintiesinthedeterminationoftherealprecipitationamounts.
Snowmetamorphismisdifficulttoquantifyduetothelargenoisecreatedbythespatialvariability,requiringalargenumber
ofsampleseveryday.Usingpassivemicrowavesatellitedata,Picardetal.(2012)arguethatthegrainindexisanindicatorof
thecoarseningofsnowgrainsandshowitsincreaseinsummertobeanti-correlatedwiththeintegratedsummerprecipitation
20 amount.Supersaturationisestimatedfromthecombinedmeasurementsofhumidityandtemperature,bothofwhicharecom-
plexified by the extreme conditions in Antarctica (Genthon et al., 2016). Including water isotopic composition as a tracer of
theinteractionsbetweenthesnowpackandtheatmosphericboundarylayercouldhelprefineourknowledgeoftheprocesses
involvedinthehydrologicalcycleintheseregions.
25 Recent studies have focused either on the monitoring of the isotopic composition of the snow pack on the East Antarctic
Plateau (Touzeau et al., 2016), of the precipitation (Fujita and Abe, 2006; Landais et al., 2012; Stenni et al., 2016), or of
the atmospheric water vapour (Casado et al., 2016b; Ritter et al., 2016); exploring their links to climatic parameters and the
implicationsforpost-depositionprocessesduringthearchivaloftheclimaticsignalbythesnowisotopiccomposition.Here,
westudytheisotopiccompositionofthecontinuumbetweenatmosphericvapour,precipitation,surfaceandburiedsnow.To
30 doso,wecombinedifferentdatasetsfromtheEastAntarcticPlateau,basedonpublishedstudiesandnewresults,inorderto
qualitativelycharacterisethedifferentprocessesaffectingsurfacesnowisotopecompositionatdifferenttimescales.Wefirst
reportandcomparethedifferentmethodologiesappliedforsamplingsurfacesnow,snowpits,precipitationandwatervapour
intheatmosphere(Section2).Then,wepresenttheresultsfromthesedifferentstudiesincludingsurfacesnowmeasurements
overseveralyears,precipitationmeasurements,vapourandsnowmeasurementsandsnowpitssampling(Section3).Finally,
3
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
wediscusstheimpactofpost-depositionprocessesatthesnowsurfacethroughtheexchangesbetweenthesnowandthevapour
andwithinthefirn(Section4)beforesummarisingourkeyconclusions.
2 Sites,materialandmethods
2.1 Sites
5 The East Antarctic Plateau is a high elevation area, over 2500 metres above sea level (ma.s.l.) covered with snow and ice
spreadingonmostoftheeasterncontinentalpartofAntarctica(Fig.1).TheEastAntarcticPlateauischaracterisedbymean
annualtemperaturesbelow 30 Candaccumulationbelow80kg.m 2.yr 1,asillustratedinFig.1.
◦ − −
−
Annual mean surface Samples available
air temperature (°C) 0o Kohnen
-5 3 0o W 30oE 2S usmnomwepri t2s0 14 /15
-10
Vapour monitoring
Summer 2013/14
-15
oW 6 Vostok
60 Kohnen 0o 7 snowpits
E
-20 from 1999 to 2012
Precipitation samples
in 2000
-25 S2
oW South Pole 90 1 snowpit
0 o Summer 2012/13
9 E
-30 Vostok
S2 Dome C
Dome C 5 snowpits
80oS from 1977 to 2015
-35 Precipitation samples
1 oE from 2008 to 2011
-40 20Wo 120 Sfroumrfa 2c0e1 s1n otow 2 015
70oS Vapour monitoring
Summer 2014/15
-45
-50 150oW 1 5 0o E S1o suntohw Ppiot ilne 1978
180oW 1 snow pit in 1989
Figure1.MapofAntarcticahighlightingtheEastAntarcticPlateau(greyline=contourof2500ma.s.l.elevation)indicatingthelocation
ofthesamplingsites(solidsquares)includedinthiswork.Coloursindicatetheannualmeansurfaceairtemperatureat2mmodifiedfrom
theERA-interimdatasetfrom1979to2009(NicolasandBromwich,2014).
4
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
ThisstudymainlyfocusesonDomeC,thesiteoftheConcordiaoverwinteringstation,enablingyear-longoperationsand
thusgivingtherareopportunitytostudytheentireseasonalcycleofisotopiccomposition.Weextendtheresultstotheentire
East Antarctic Plateau by comparing the data from Dome C to observations from the Kohnen, Vostok and Amundsen-Scott
South-PolestationsandfromthepointS2whichisoneofthedrillingsitesofthecampaignExplore-VanishjoiningDomeC
5 andVostok(seeFig.1).TheselocationsspanalargerangeofclimaticconditionsoftheEastAntarcticPlateauasillustratedon
Table1.
Table1.Climaticconditionsatthedifferentsitesusedinthisstudy(Alley,1980;Petitetal.,1982;WendlerandKodama,1984;Oerteretal.,
2000;Ekaykinetal.,2002;vanAsetal.,2007;Lazzaraetal.,2012;Caseyetal.,2014;Genthonetal.,2015;Touzeauetal.,2016;Laepple
etal.,2016)
Altitude AWSmean 10mfirn Accumulation Meanwind
Site Location
(ma.s.l.) temperature( C) temperature( C) (kg.m 2.yr 1) speed(m.s 1)
◦ ◦ − − −
Kohnen 75.0 S-0.1 E 2892 -42.2 -44.5 62-73 4.5
◦ ◦
Vostok 78.5 S-106.8 E 3488 -55.2 -57 21 5.1
◦ ◦
S2 76.3 S-120 E 3229 NA -55.1 21 NA
◦ ◦
DomeC 75.1 S-123.3 E 3233 -52.4 -54.3 27 3.3
◦ ◦
SouthPole 90 S-0 E 2835 -49.3 -50.8 80 4.1
◦ ◦
2.2 Surfacesnowandprecipitationsampling
Precipitation and surface snow have been sampled at Dome C regularly by different teams since 2008. Here, we report new
measurementsofprecipitationandsurfacesnowtogetherwithpreviouslypublisheddatafromStennietal.(2016)andTouzeau
10 et al. (2016) (see Table 2). Because different teams were in charge of the different sampling activities, the protocols differ
betweentheyears.
Thesamplingprotocolofthe2011campaign(SUNITEDC)hasbeenpreciselydescribedbyTouzeauetal.(2016):theupper
first millimetres of snow (1 to 5mm) were gathered every 1-2 weeks using a metallic blade over a surface of 20 per 20cm.
15 Thisleadstosamplesofapproximately20mL.Thesamplingareaswererandomlypickedprovidedthesurfacewasflat.
DuringtheNIVOproject(from2013to2015),thesurfacesnowwasgatheredbysamplingroughly15mmofsnowwitha
corningflaskoverasurfaceof20per10cm.Thisledtosamplesofapproximately50mL.Thesamplingareasof2013/14were
chosenrandomlyina100per100m"cleanarea"neartheAtmosphericShelterinparallelwithdensityandspecificsurfacearea
20 (SSA)measurements(seesection2.4).Twosampleswerecollectedduringeachcollectandwepresentheretheaveragevalue
ofthetwosamples.Inaddition,duringsummer2013/14,regularsamplingsofsurfaceandsub-surfacesnowwereperformed
foralmost2months.Thesurfacesamplesweregatheredusingacorningflaskfrom0to3cmdepth.Thesub-surfacesamples
weregatheredbythesametoolfrom3to6cmdepth.In2014/15,anadditionalsamplingtookplacewithintheGLACIOproject
5
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
twiceadayfromDecember2014toJanuary2015nearthelocationoftheinletusedforwatervapourmonitoring(Seesection
2.4andCasadoetal.(2016b))followingthesameprotocol.
SamplingofsurfacesnowandprecipitationisotopiccompositionwerecarriedoutinparallelbytheItalianwinterovercrews
5 (programPRE-REC).Precipitationsampleshavebeencollectedallyearroundona80per120cmwoodentablestanding1m
abovethegroundlevel800mfromConcordiaStationfrom2008to2011.Thesampleswerecollectedat1a.m.everydayif
theamountwassufficient.Thesurfacesnowsamplesweregatheredfromanadjacentwoodenplateof80per120cmatground
level.Iftheamountofsnowonthissecondtablewassufficient,snowsampleswerecollected.Bothprecipitationandsurface
snowsamplesweresealedintodate-labelledplasticbagsandpreservedinfrozenstateuntildeliveryandmeasurementinItaly.
10 Fortheprecipitationsamples,theprotocolisdetailedbyStennietal.(2016).Itisimportanttonotethattheprotocolofsurface
snowsamplingfromthePRE-RECcampaigndiffergreatlyfromtheprotocolsfromtheNIVOandSUNITEDCprogramsdue
tothepresenceofthewoodplate.
Table2.Summaryofthedifferentcampaignsofsurfacesnowandprecipitationsamplingspresentedhere.
Resolution
Project Location Years Reference
(days)
SUNITEDC(French) Surfacesnow 2011 7 (Touzeauetal.,2016)
Precipitation 2008to2011 1 Partiallyin(Stennietal.,2016)
PRE-REC(Italian)
Surfacesnow 2012and2014 7 Thisstudy
Surfacesnow 2013to2016 3
NIVO(French) Thisstudy
Sub-surface 11/2013to01/2014 1
GLACIO(French) Surfacesnow 12/2014to01/2015 1 Thisstudy
2.3 Snowpitssampling
15 We present profiles of isotopic composition sampled in snow pits at Dome C : two unpublished profiles from the first pre-
liminary campaigns at Dome C in 1978 and two new snow pit profiles obtained in 2014/15, dug 50m apart in parallel with
surfacesnowsamplingandvapourmonitoring.Foroneofthem,snowtemperatureanddensityprofileswereestablished.The
samples were taken in plastic flasks and analysed later on in the laboratory. To extend the results to other sites of the East
AntarcticPlateau,weadditionallypresentsnowpitsamplingsperformedthroughseveralcampaignsoverdifferentsitesofEast
20 Antarcticawhichwererealisedandanalysedbydifferentteams.
6
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
Table3.Summaryofthedifferentsnowpitspresentedinthisstudy.
Resolution Number
Station Years Reference
(cm) ofpits
2001to2015 2to5 6 Ekaykinetal.(2002,2004,2009)
Vostok
2012/13 3 1 Touzeauetal.(2016)
Kohnen 2014/15 3 2 Thisstudy
1977/78 1to3 2 Thisstudy
DomeC 2012/13 3 1 Touzeauetal.(2016)
2014/15 1.5to5 2 Thisstudy
S2 2012/13 3 1 Touzeauetal.(2016)
1978 2 1 Jouzeletal.(1983)
SouthPole
1989/90 1.1 1 Whitlowetal.(1992)
Two new isotopic composition profiles from Kohnen are extracted from trenches, following the methodology reported in
Münchetal.(2016)butdownto3.6mdepthsampledata3cmverticalresolution.Thetwoprofilesareseparatedbyapprox-
imately 500m. A large number of snow pits from Vostok station are presented here, they have been previously described in
Ekaykinetal.(2002,2004)andEkaykinandLipenkov(2009).Wecombinetheresultsfromsixsnowpitswithdepthsvarying
5 from2.5mto12mandaminimumresolutionof5cm.Inaddition,snowpitsfromtheExplore-Vanishcampaignareincluded
comprisingone3.5mdeepsnowpitfromVostok,one2.6mdeepfromS2andone2mdeepfromDomeC,alloftheminclud-
ing triple isotopic compositions (δ18O, δ17O and δD) published in Touzeau et al. (2016). Finally, we include two snow pits
fromSouthPole(Jouzeletal.,1983;Whitlowetal.,1992).
2.4 Atmosphericandsnowsurfacemonitoring
10 Water vapour isotopic composition has been measured at Kohnen station in 2013/14 (Ritter et al., 2016) and at Dome C in
2014/15 (Casado et al., 2016b). In both cases, to reduce the noise, the dataset were averaged to hourly resolution and cover
approximately one month. In parallel to water vapour isotopic composition monitoring, surface snow was sampled once to
twiceaday.Foraperiodfrom27hoursto72hours,thesurfacesnowwassampledeveryhourtoevaluatethediurnalcycleof
boththevapourandthesnowisotopiccomposition(seesection2.2).
15
Dome C hosts a large set of instruments probing the troposphere and the firn justifying to focus this study on this site.
Here, we make use of temperature, wind speed and humidity measurements from the 45m meteorological profiling system
described by Genthon et al. (2013). The temperature and humidity observations are performed using ventilated thermohy-
grometersHMP155andarethereforefreeofradiationbiases(Genthonetal.,2011).Thetemperaturereanalysisproduct(ERA
20 interim) has been compared to ventilated automatic weather station data (AWS) from Genthon et al. (2013) and we found
7
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
a good agreement at the seasonal scale and fairly good agreement at the event scale (not shown here). Depending on data
availability(astheventilatedAWSwereinstalledatDomeCin2009),wewilluseeitherERA-interimormeasurementsfrom
AWS. An intercomparison when the two datasets are overlapping reveals that most of the variability from the day-to-day to
the seasonal and inter-annual scales in captured by ERA-interim and major differences appear only for the evaluation of the
5 diurnal cycle (not shown). Wind speed and direction are measured using Young 05103 and 05106 aerovanes. Snow surface
temperatureismeasuredwithaCampbellscientificIR120infraredprobelocated2mabovegroundlevel.
Finally, we include grain index observations (Picard et al., 2012) obtained by satellite measurements. The grain index is
used as an indicator of the evolution of the size of the snow grains, and provides a qualitative evaluation of metamorphism.
10 Whenavailable,weincludeSurfaceSensitiveArea(SSA)measurementsalsoasanindicatorofmetamorphism(Liboisetal.,
2015).Theseopticalmethodsarecompletedwithsnowsurfaceobservations.Frostdepositionwasmonitoredwithatimelapse
ofthegrowthofhoaratthesurface(seethevideoathttps://vimeo.com/170463778).Animageprocessingscriptwasusedto
characterisethegrowthofafewcrystalsatthesurfaceofthesastruga.
2.5 Modellingapproaches
15 To highlight the impact of post-deposition processes, it is necessary to present how the surface snow isotopic composition
differs from the initial precipitation signal formed during the Rayleigh distillation. Here, we make use of the Rayleigh-type
Mixed Cloud Isotope Model (MCIM) developed by Ciais and Jouzel (1994) which computes the Rayleigh distillation along
theairmassestrajectories.Themodelincludesmicrophysicalpropertiesofcloudsandinparticulartakesintoaccountmixed
phaseconditions.ItistunedwithtriplesnowisotopiccompositionmeasuredalongatransectfromTerraNovaBaytoDomeC
20 (Landaisetal.,2008).ThistuninghasbeenprovensuitabletoevaluatethevariationsofisotopiccompositionatDomeC(Win-
kler,2012).Thiswillprovideacomparisonbetweenthespatialandthetemporalslopeofprecipitationisotopiccompositionat
theseasonalscale.
3 Results
Inthissection,wereviewtheresultsfromthedifferentdatasets,illustratingthedifferentstepsofthearchivalofclimaticsignal
25 bythesnowisotopiccomposition,fromtheprecipitationtotheburiedsnow(seeFig.2).
WefirstpresentprecipitationisotopiccompositionvariationsbasedondatafromStennietal.(2016)andadditionalnewdata.
Wethenpresentournewdataofsurfacesnowisotopiccompositioncomparedtothevariationsin2msurfaceairtemperature,
thegrainsizeindexandtheprecipitationisotopiccomposition,inordertoevaluateattheday-to-dayandattheseasonalscales
30 thedifferencebetweensurfacesnowandprecipitationisotopicsignals.Wethenreportshorttimescaleparallelmeasurements
ofvapourandsurfacesnowisotopiccomposition,providinginputsononeofthemajorcomponentofsummermetamorphism
onsurfacesnowisotopiccomposition:thediurnalcyclesofsublimation/condensation.Wefinallycomparetheisotopiccom-
8
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
Temperature
Free gradient
atmosphere
Eddy
diffusion
Precipitation input
Atmospheric Sublimation
condensation
boundary Ri P
layer v v
Exchange Snow
Ri with the precipitation
P
vapour
Molecular
Surface Ri P diffusion
snow 0 sat
Interstitial
vapour Ri
S
Molecular diffusion
in the interstitial air
Deeper Ri
snow N
Figure2.Schematicofthedifferentcontributionstothesnowisotopiccomposition(Ri standsforthecompositionofisotopeiinthephase
X
X)inremotePolarRegions:abovethesurface,boththeprecipitationandthesublimation/condensationcyclescancontributetothesurface
composition; in the open-porous firn below the surface, the snow can exchange with the air below the surface, enhanced or not by wind
pumping.Deeperinthefirn,moleculardiffusionintheinterstitialairaffectsthesnowisotopiccomposition.
position of the surface, sub-surface and buried snow to evaluate the processes involved during the archival of the isotopic
compositionsignal.
3.1 Precipitationisotopiccomposition
Inthissection,wepresentprecipitationisotopiccompositiondataatDomeCfromStennietal.(2016)depicting3complete
5 annualcyclesfrom2008to2010,completedbynew,unpublisheddatafrom2011(Fig.3).
AtDomeC,theprecipitationisotopiccompositionpresentsalargevariabilityattheday-to-dayscaleandaregularseasonal
cycle.Attheseasonalscale,precipitationisotopiccompositionisrelativelywellcorrelatedtolocaltemperaturewithaslopeof
0.46‰ C 1,thisslopeissimilartotheoneobtainedbyStennietal.(2016)fortheyears2008to2010of0.49 0.02‰ C 1
◦ − ◦ −
±
10 (R2=0.63,n=500).Noapparentlagbetweentemperatureandisotopiccompositionvariationsisobserved.
Comparedtootheryear-longprecipitationsamplingontheEastAntarcticPlateau,thisslopeislowerthanatDomeF(0.78
‰/ C withR2=0.78(FujitaandAbe,2006))andhigherthanatVostok(0.26‰/ C withR2=0.58(Touzeauetal.,2016)).
◦ ◦
Insummer,wesystematicallyobserveprecipitationδ18Oabove-40‰atDomeC,whereasinwinter,δ18Ovaluesbelow-65
15 ‰aresystematicallyobserved.
9
TheCryosphereDiscuss.,doi:10.5194/tc-2016-263,2016
ManuscriptunderreviewforjournalTheCryosphere
Published:17November2016
c Author(s)2016.CC-BY3.0License.
(cid:13)
‰)-40
n (
o-50
ati
pit
ci-60 600
e
pr
O 500
8 -70 G
1δ ra
400in
In
300d
e
x
200 (A
-20 .U
.)
100
C)-30
e (°-40 0
ur
at-50
er
p
m-60
Te 0.8(mS
-70 mn
0.4 wow
-80 0.0.efa
.)ll
1/2008 7/2008 1/2009 7/2009 1/2010 7/2010 1/2011 7/2011
Figure3.Fouryears(2008to2011)ofmonitoringatDomeCofthevariationsofprecipitationisotopiccompositionfromthePRE-REC
campaign(Stennietal.,2016)(δ18O,green,dots:rawdata,line:monthlyaverage)insurfaceairtemperaturefromthereanalysisERA-interim
(redline),grainindexfromsatelliteobservations(blackline)andsnowfallamountcalculatedfromthereanalysisERA-interim(blackbars).
3.2 Surfacesnowisotopiccomposition
Here,wepresentmeasurementsofsurfacesnowisotopiccompositionatDomeCfromDecember2010toJanuary2016(Fig.
4) combining results from Touzeau et al. (2016) with new data presented for the first time in this study from the PRE-REC,
NIVOandGLACIOprojects.Thedatasetincludesthreecompleteannualcyclesofsurfacesnowisotopiccomposition(in2011,
5 2014and2015)andpartofthe2012cycle,withtherespectivetemperaturevariationsfromAWS(Genthonetal.,2013)and
theprecipitationevents(fromreanalysisproducts).NoteherethatweusetheavailabledatafromAWSinthissectionandnot
reanalysisproductsasinsection3.1(seesection2.4).
First,wefocusonthespatialvariabilityimpactonthemeasurements.Todisentanglethelocal(below1km)spatialvariabil-
10 ity from the temporal variations of the surface snow isotopic composition (Fig. 4), we compare the duplicate measurements
realisedduringtheyear2014(Fig.5).Indeed,forthisyear,severalsetsofmeasurementsareavailable:onesampledatafixed
locationonawoodsurface(PRE-REC,bluedots)andonesampledrandomlyfromthesnowsurfaceinalargefield(NIVO,
10