BachelorThesis

VariabilityoftheIsotopicandHydrochemicalComposition

ofLakeBol'shoeToko,SEYakutia,Russia

Presentedtothe

InstituteofEarthandEnvironmentalSciences

UniversityofPotsdam

Inpartialfulfillmentofthe

requirementforthedegree

BachelorofScienceinGeosciences

by

TillHainbach

Supervisedby

Dr.HannoMeyer

apl.Prof.Dr.BernhardDiekmann

Dr.BorisBiskaborn

Potsdam,November2016

I

TableofContents

TableofFigures.................................................................................................................III

ListofTables.....................................................................................................................III

ListofAbbreviations..........................................................................................................IV

Abstract.............................................................................................................................V

Zusammenfassung.............................................................................................................VI

1 Introduction................................................................................................................1

2 StudyArea..................................................................................................................3

2.1 Limnologicalsetting........................................................................................................3

2.2 Geologicalsetting...........................................................................................................5

2.3 Climaticsetting...............................................................................................................5

3 Materials&Methods..................................................................................................7

3.1 Stableisotopegeochemistryinwateranalysis................................................................7

3.1.1 Fundamentalsofstableisotopegeochemistry..................................................................7

3.1.2 Fractionationofstableisotopes........................................................................................8

3.1.3 Effectsonstableisotopeswithinthehydrologicalcycle.................................................11

3.1.4 Stableisotopemeasurements.........................................................................................12

3.2 Analyticalmethodsforhydrochemicalwateranalysis...................................................13

3.2.1 ICPOES............................................................................................................................13

3.2.2 Analysisofbicarbonateinwater.....................................................................................14

3.2.3 Ionexchangechromatography........................................................................................15

3.2.4 pH-valuemeasurementsinwater...................................................................................15

3.2.5 Measurementofdissolvedoxygen(DO).........................................................................16

3.3 Fieldwork......................................................................................................................16

4 Results......................................................................................................................17

4.1 VariabilityoftheisotopiccompositionatLakeBol’shoeToko.......................................17

4.1.1 SpatialvariationoftheisotopiccompositionatBol’shoeToko......................................17

4.1.2 Isotope-depthprofilesfromLakeBol’shoeTokoanditssurroundings...........................20

4.2 HydrochemicalcompositionofBol’shoeToko...............................................................23

5 Discussion.................................................................................................................25

5.1 WaterandprecipitationsourcesforLakeBol’shoeToko...............................................25

II

5.2 TheisotopicsignalofLakeBol’shoeTokoanditsspatialvariations...............................28

5.3 Isotope-depthrelationshipatLakeBolshoeToko..........................................................30

5.4 Discussionofthehydrochemicalcomposition...............................................................32

5.5 LakeBol’shoeTokoinregionalcomparison...................................................................34

6 Conclusions...............................................................................................................36

7 Outlook....................................................................................................................37

References.......................................................................................................................38

Appendix.............................................................................................................................i

Acknowledgments..............................................................................................................v

III

TableofFigures

Figure1:TopographicmapofCentralandEasternSiberia.......................................................3

Figure2:MapofLakeBol'shoeTokoanditslimnologicalandgeologicalsetting.....................4

Figure3:ClimatediagramforTokoRS(afterWalterandLieth(1960))....................................6

Figure4: Fractionationprocessesof stablewater isotopes and their effectson ameteoricwaterline........................................................................................................................10

Figure5:Schemeofamassspectrometer..............................................................................12

Figure6:SchemeofthePerkinElmerOptima8300ICPOES..................................................14

Figure7:δ18O-δD-plotforallwatersamplesandGNIPdatafromYakutsk............................18

Figure8:IsotopiccompositionofsurfacewatersamplesfromLakeBol’shoeToko..............18

Figure9:Isotope-depthandtemperature-depthprofilesatPG2208.....................................20

Figure 10: Isotope-depth and temperature-depth profile at PG2122 “Lagoon”, SE of LakeBol'shoeToko..................................................................................................................22

Figure11:Isotope-depthandtemperature-depthprofileforsitePG2131"BaniaLake".......22

Figure12:Piper(1944)Plotforallwatersamplesofdifferentsamplesites..........................23

Figure13:AnnualmeanδDandδ18Oinprecipitationpatterns(Isoscapes)forNorthAsia....26

Figure 14: HYSPLIT back trajectory frequencies prior to both 6-day precipitation events inAugust2012(06-08.08.2012(A),17.-22.08.2012(B))andtotheprecipitationevent1-3April2013(C)...................................................................................................................27

Figure15:Isotope-depthprofilesforbothwater(red)andlakeice(turquoise)atsitePG2208,LakeBol’shoeToko..........................................................................................................30

ListofTables

Table1:Terrestrialabundancesofstableoxygenandhydrogenisotopes...............................7

Table2:meanisotopiccompositionofsnow,lakeice,andwatersamplesfromtherespectivelakebasinorwaterprofile..............................................................................................19

Table3:IsotopiccompositionofsnowandicesamplestakenatLakeBol’shoeToko..............i

Table4:IsotopeandhydrochemistrydataforallwatersamplestakeninMarch2013...........ii

Table5:HydrochemistrydataforallwatersamplestakeninMarch2013.............................iii

Table6:IsotopedataforwatersamplestakeninAugust2012...............................................iv

IV

ListofAbbreviations

a.s.l. abovesealevel

BP beforePresent(before1950)

BT Bol’shoeToko

d-excess Deuteriumexcess

DIC DissolvedInorganicCarbon

GMWL GlobalMeteoricWaterLine

GNIP GlobalNetworkofIsotopesinPrecipitation

HDW2 MixedstandardwaterfromthePotsdamregion

HTM Holocenethermalmaximum

IC IonExchangeChromatograph

ICPOES Inductive-CoupledPlasmaOpticEmissionSpectroscopy

IRMS IsotopeRatioMassSpectrometer

KARA KaraSeaWater(standard)

LMWL LocalMeteoricWaterLine

NGT NorthGreenlandTraverse(standard)

OIPC OnlineIsotopesinPrecipitationCalculator

Precip. Precipitation

SEZ SevernajaZemljawater(standard)

Temp. Temperature

V

Abstract

High latitudes of the northern hemisphere are most vulnerable to climate warming, but

imposeagreatthreatduetopositivefeedbackmechanism,suchasenhancedgreenhouse-

gasemissionsasaconsequenceofpermafrostdegradation.IntheRussianFar-East,however,

predictions arebiaseddue to large researchgaps.Hence, further investigationson recent

climatepatternsareessentialtoachievebetterestimatesforfutureenvironmentalchangein

borealRussia.

In this context, open surface waters, such as lakes, provide valuable information about

precipitationsourcesandseasonalvariabilityinremoteareasofSiberia.Stablewaterisotopes

are good climateproxiesdue to temperaturedependent fractionationprocess. Therefore,

water,iceandsnowsamplesweretakenatalake(Bol’shoeToko,BT)inalittleexploredregion

inSouthernYakutiain2012and2013.Analysesoftheisotopicandhydrochemicalcomposition

werecarriedouttoobtainaprofoundknowledgeofthepresenthydrologicalregime.

WaterisotopeanalysesatLakeBol’shoeTokoshowonlylittlevariationsspatiallyaswellas

throughoutthewatercolumn.Themeanisotopiccompositionofδ18O=-18.2±0.2‰andδD

=-137±1‰shownosignificantseasonalvariationscomparingasummerandwinterprofile.

There is no indication for evaporationenrichment foundat LakeBol’shoeToko.However,

fractionationalterstheisotopiccompositionofsurfacewatersduringice-coverformation.In

contrast,waterofthesidelake“BaniaLake”(EastofLakeBol’shoeToko)isenrichedinheavy

isotopes, indicating evaporative enrichment during summer, whereas water in a lagoon

(South-EastofLakeBol’shoeToko)haveaslightlylowerisotopiccomposition.Watersfromall

three lakes are of Ca-Mg-HCO3-type and show unpolluted freshwater conditionswith low

conductivity. However, nitrate concentration in the lagoon are at a critical level for algae

growth.

All inall,LakeBol’shoeTokoisanoligotrophic,well-mixed,openthrough-flowlakesystem

withnopronouncedseasonalvariability.Changesinisotopicandhydrochemicalcomposition

ofthelagoonandBaniaLakearedirectlylinktothegeologicalandgeomorphologicalsetting

of Lake Bol’shoe Toko, as precipitation and substantially surface run-off control the

hydrologicalregime.

VI

Zusammenfassung

DiehohenBreitendernördlichenHemisphäresindvomKlimawandelammeistenbetroffen,

aberstellenaufgrundvonpositivenRückkopplungsmechanismenaucheinegroßeGefahrdar,

wiezumBeispielerhöhteTreibhausgasemissionaufgrundvonPermafrostdegradation.Jedoch

sindVorhersagenfürdasfernöstlicheRusslanddurchgroßeForschungslückenverzerrt.Um

zukünftige Umweltveränderungen im borealen Russland besser vorhersagen zu können,

benötigt es weiterer Studien über die rezenten Klimamuster. In diesem Zusammenhang

können offene Oberflächengewässer, wie Seen, wertvolle Information über

Niederschlagsquellen und saisonale Schwankungen in den abgelegenenGebieten Sibiriens

liefern.WegenihrertemperaturabhängigenFractionierungsindstabileWasserisotopengute

Klimaproxies.Daherwurden2012und2013Wasser-,Eis-undSchneeprobenauseinemSee

(Bol’shoeToko,BT)ineinerwenigerforschtenRegioninSüd-Yakutienentnommen.Analysen

der Isotopen- und hydrochemischen Zusammensetzung wurde durchgeführt, um so ein

tiefgründigesVerständnisderrezentenHydrologiezuerhalten.DieIsotopenanalysenzeigen

nur geringe Schwankung, sowohl in der Fläche als auch in der Wassersäule. Die

durchschnittlicheIsotopenzusammensetzungvonδ18O=-18.2±0.2‰undδD=-137±1‰

zeigtekeinesignifikantensaisonalenVeränderungenzwischenSommer-undWinterprofil.Es

gab keine Anzeichen für evaporativen Anreicherungen im Bol’shoe Toko See. Jedoch

verändern Fraktionierungsprozesse die Isotopenzusammensetzung von Oberflächenwässer

währendderAusbildungderSeeeisschicht.ImGegensatzdazuwarenWasserprobenausdem

Nebensee „Bania See“ (im Osten des Bol’shoe Toko Sees) mit schwereren Isotopen

angereichert,wasaufevaporativeAnreicherungindenSummermonatenhindeutet.Indessen

hattenWasserprobenausderLaguneimSüdostendesBol’shoeTokoSeeseineleichtleichtere

Isotopenzusammensetzung.GewässerprobenderdreiuntersuchtenSeenwarenvomCa-Mg-

HCO3-Type und zeigten nicht verschmutzte Frischwasserbedingungen mit geringer

Leitfähigkeit. Jedoch waren die Nitratkonzentrationen in der Lagune auf einem kritischen

NiveaufürdasAlgenwachstum.

AllesimallemistderBol’shoeTokoSeeeinoligotropher,gutgemischter,offenerDurchfluss-

SeemitkeinerausgeprägtensaisonalenSchwankung.Veränderungen inder Isotopen-und

hydrochemischenZusammensetzungderLaguneunddesBaniaSeessinddirektverknüpftmit

dem geologischen und geomorphologischen Hintergrund des Bol’shoe Toko Sees, da

NiederschlagundvorallemOberflächenablaufdieHydrologiebeeinflussen.

1

1 Introduction

Highlatitudesofthenorthernhemispherearemostvulnerabletoclimatewarming(Zhanget

al.,2000,ACIA,2004).InborealRussia,modelspredictanincreaseofannualmeansurface

temperatureofup to+11°C (Giorgetta,2012). Increasing surface temperaturesenhanced

permafrostthawingandsnowcovermelting,thusleadingtofurtheremissionofgreenhouse

gases (e.g. methane) from soils and albedo reduction, respectively. Therefore, ongoing

warming of high latitudes results in further global warming due to positive feedback

mechanisms (Schuur and Abbott, 2011). Accurate estimates on environmental impact,

however,arebiasedduetolargeresearchgapsinunderstandingthesub-recentpaleoclimate

intheRussianFar-East(Milleretal.,2010).

Here,stablewaterisotopescanprovidevaluableinformationtoimprovetheunderstanding

oftherecentclimatesystem.Sincethemid1950s,stablewaterisotopeshavebeenusedto

investigate the hydrological cycle and climate patterns (Craig, 1961a, Dansgaard, 1964,

Rozanskietal.,1993,Araguás-Araguásetal.,1998).Nonetheless,mostofthesestudiesare

basedonlongtermobservationoftheisotopiccompositioninprecipitation.

Suchobservations,however,areinsufficientforlargepartsoftheremoteareasofSiberia,but

informationcanbederivedfromopensurfacewaters.Firststudiesofstableisotopebehavior

in lake water hydrology were carried out by Craig and Gordon (1965) and subsequently

improved(e.g.Dincer,1968,Zuber,1983,Gat,1995).Withthebeginningofthenewmillennia,

isotopic studies were conducted investigating the linkage between surface waters and

precipitationonabroaderregionalscale(Gibsonetal.,2002,Ichiyanagietal.,2003,Mayret

al.,2007,GibsonandReid,2010).

Additionally,hydrochemicalanalysishasbeenwidelyusedtoobtainkeyinformationonthe

hydrology controlsof lake systems,e.g. in identifying sourcewateranddifferentdrainage

regions as well as acquiring knowledge about the geogenic background and limitation of

aquaticbiota(e.g.ParnachevandDegermendzhy,2002,Rogoraetal.,2003).Furthermore,

information aboutwater hydrochemistry is essential for assessing possible anthropogenic

influencesonlimnologicalecosystems(e.g.Reimannetal.,1999).

Consequently, the combination of stable isotope and hydrochemical analyses leads to a

profoundknowledgeaboutthehydrologicalregimeofsurfacewatersystems.Thisincludes

informationsuchasrecentlaketemperature,isotopiccomposition,precipitationandwater

2

sourcesandtheirrespectiveseasonalchangesaswellaspossiblechangesofwaterlakelevel

andinputsignalsovertime.

On thisbasis,multi-proxy studiesof lake sediments cores canprovidehigh resolutionand

continuous information on environmental and climatic change (Leng and Barker, 2006),

hence,allowingpaleoclimatereconstructionfromaterrestrialperspective.

At the Alfred-Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI),

bioindicators,sedimentologicalandgeochemicaldataoflakesedimentcoresfromdifferent

lake systems through Central and Eastern Siberiawere investigated (e.g. Biskaborn et al.,

2012,Biskabornetal.,2013,Nazarovaetal.,2013,Schleusneretal.,2015)withintheSibLake

Program (Eastern Siberian Lakes (SibLake Programme)). Two transects of north-south and

west-eastorientationaimtodistinguishdifferentclimaticinfluencesonpaleoenvironmental

changes,e.g. thetemporaldelayoftheHolocenethermalmaximum(HTM)fromnorthto

southYakutia(Biskabornetal.,2016).

Inthiscontext,theinvestigationofLakeBol’shoeTokoaimstoextendtheunderstandingof

recentclimatevariabilityinsouthwarddirection.Previouslyconductedresearchindicateda

pristinenaturalenvironment,thoughKonstantinov(2000)reportedpossibleanthropogenic

influencesduetoenhancedcoalminingactivityinsouthernYakutiaadjacenttoLakeBol’shoe

Toko.

SeveralwatersamplesandsedimentcoreswereretrievedduringajointexpeditionofAWI

andtheNorth-EasternFederalUniversityofYakutsk(NEFU)in2013.Thisthesisispartofa

seriesofthesesonLakeBol’shoeTokothatarebasedonsamplestakenduringtheMarch2013

expedition.Firstassessmentsonsedimentology(Löffler,2016)andtaxonomyofchironomids

(Weniger, 2016) and diatoms (Dreßler, 2016) have already been carried out. A thesis on

oxygenisotopesinsubsurfacediatomsisinprogress(Wollenweber,2017,inprep.).Inthis

context, the presented study aims to provide import background information about the

hydrological regime at Lake Bol’shoe Toko. For this, the isotopic and hydrochemical

composition of the lake water, as well as in snow and ice samples were analysed and

interpretedregardingthelocalgeomorphologicalandgeologicalsettinganditscontribution

tolakewatervariability.Thefindingsarethendiscussedwithintheregionalcontext.

3

2 StudyArea

TheRepublicofSakhaorYakutiacoversmostofthecentralpartofSiberia.Itextendsfrom

theGulfofKhatangaeastwardoverthenortheastSiberianLowlandtotheKolymaGulf.From

thereitsbordertrendssouth-westwardstotheAldanUpland,crossingtheNortheastSiberian

Highlands.TheSouthernborderismarkedbythesouthernedgeoftheAldanUplandandthe

Tokinsky-StanvoimountainrangeswhichalsoformthefrontieroftheNerjungricoaldeposits.

ThewesternfrontieroftherepublicofSakhatrendsfromtheKhatangaGulfsouthwardtothe

Baikalianranges.

2.1 Limnologicalsetting

TheLakeBol’shoeTokoislocatedat56°15’N,130°30’EinSouth-EastYakutiaattheborderof

theRepublicofSakhaandtheRegionKhabarovsk.Itis300kminlandtotheeastfromtheSea

ofOkhotskandliesat903ma.s.l.Thelakeis15kminlengthand7kminwidthandcoversa

surfaceofapproximately82.6km2(Konstantinov,2000).Ithasamaximumwaterdepthof80

matthewesternmarginofthelake,whereasthenorthernmarginisrelativelyshallow(20-10

mdeep).

Figure1:TopographicmapofCentralandEasternSiberia.

4

Figure2:MapofLakeBol'shoeTokoanditslimnologicalandgeologicalsetting.Redpointsindicate

watersamplesites.Originalmapwasmeasuredat1kmgridandthereforecontainsuncertaintiesin

water depths. Compiled by B. Biskaborn combining the data from Konstantinov (2000) and

Kornilov(1962),bothRussianliterature.

5

TheUtukriverbringswaterfromthesouthernigneouscatchment,additionallyfedbytherun

offofLakeMaloeToko(asmallerlakeoftectonicoriginapproximately3kmsouthoftheLake

Bol’shoeToko)and formsdeltaicsediments.Asecondunnamedtributary river runs intoa

shallower (<20m) lagoonat theeasternpartof LakeBol’shoeToko.The lagoon isnearly

separatedfromtheBol’shoeTokobasinandhasjustanarrowandshallowconnectionofless

than80minwidth.LakeBol’shoeTokohasonemainoutflowcalledMulamriverwhichruns

northwardalongthesoutheasternborderofYakutiaintoUzur,AldanandultimatelyintoLena

River(Konstantinov,2000).

2.2 Geologicalsetting

TheLakeBol’shoeTokoisoftectonicandglacialorigin.Itliesinadepressionformedbytwo

NW-trending right-lateral strike-slip faults (Imaevaetal., 2009) reshapedbyat least three

glacialsub-periods.Thebasin isdammedinthenorthbythemorainesoftheseglaciations

(Kornilov,1962).

AlongthesouthernmarginofthelakerunstheSouthTokinthrustfault,oneofthemostactive

faultsintheregion(earthquakesrecordedin1977and1979),wherehighlymaficgranulites

andotherhigh-pressuremetamorphicrocksoftheTokinStanovoiorogenarethrustedover

coal-richJurassicandCretaceousdeposits.Thepotentialcoalresourceswereestimateto40

billiontonsin1981beingthemostpromisingcoalbasinoftheBaikal-Amur-Mainline(Jensen

etal.,1983).Thegeodynamicactivityisalsoshowninitshighheatflow(Imaevaetal.,2009).

2.3 Climaticsetting

TheRepublicofSakhacoversthreeclimaticzones.ThecoastoftheLaptevSealieswithinthe

arctictundrazone.FurtherSouth,wherethetundravegetationgiveswaytothevasttaiga

forest,asmallstripofsubarcticclimateregimeisattached.TheSouthofYakutialieswithin

the climate regime of temperate continental climate (Shahgedanova, 2002). The Siberian

anticyclone,aregionalhighpressuresystempredominantlyactivebetweenNovemberand

March, ismainly responsible forverycoldwinters,withclearskyand lowprecipitation. In

Summer, due to the landlocked position of Central Siberia,maximum temperatures often

exceed+30°C.AstheatmosphereisdepletedinmoistureandcentralSiberiaitselfisshielded

by several orogens, precipitation ranges between 200-600 mm per year. Yakutsk’s long

weatherrecordreportsameanannualprecipitationofabout250mm/yearandameanannual

6

temperatureof-10.2°Cwithaforcontinentalsitescharacteristichightemperatureamplitude

(Januarymean,Julymean)of55K(Gavrilova,1993).

Theclosestweatherstationtothestudysiteis“TokoRS”.Itislocated10kmnortheastoflake

Bol’shoeTokoandhasalowermeanannualtemperature(-11.2°C)buthigherprecipitation

(276-579mm/year)thanYakutsk(Konstantinov,2000).Mostoftheprecipitation(50%)occurs

in the Summer months (223 mm in June-August) as rainfall whereas precipitation from

November toMarch does not exceed 30mm/month (see Figure 3).Winter precipitation

(DecembertoFebruary)justamountsto7%oftheannualprecipitation.Mostoftheyear,

meansurfaceairtemperaturesarebelowthefreezingpoint(October-April)butexceed0°Cin

earlytolatesummer(MaytoSeptember).

AtLakeBol’shoeToko,Konstantinov(2000)reportslowertemperaturemeasurementsasa

resultofcoldwaterdischargefromthemountainsandhighvolumeoficeduringwinter.

Figure3:ClimatediagramforTokoRS(afterWalterandLieth(1960)).Climatedatarecordtakenfrom

NOAA.Darkbluebarsindicateprobablefreezing;lightbluebarsindicatepossiblefreezing.Thewater

saturationisgiventhroughouttheyear.

7

3 Materials&Methods

3.1 Stableisotopegeochemistryinwateranalysis

3.1.1 Fundamentalsofstableisotopegeochemistry

Isotopesaredefinedasnuclideswhichhavethesamenumberofprotonsbutdiffer inthe

numberofneutrons.Hence,thesenuclidesbelongtothesameelementbutaredifferentiated

bytheiratomicweightdefinedbythesumofprotonsandneutrons.Dependingonthenumber

of neutrons an isotope can be stable or unstable. Unstable (radioactive) isotopes can

spontaneouslydisintegrateintootherisotopes(ofthesameoranotherelement)bydifferent

modesofdecaywhilststableisotopesdonotdecaywithindetectionlimits(ClarkandFritz,

1997,Hoefs,2015).About300stable isotopesexistworldwide(Hoefs,2015),thisresearch

howeverfocusesonwiththestablehydrogen(H),andoxygen(O)isotopesonly,whichare

alsocalledstablewaterisotopes.

There are two stable hydrogen isotopes, 1H and 2H (the latter also called deuterium, D),

whereasoxygenhasthreestableisotopes(16O,17O,18O),whichdifferintheiratomicmassand

theirterrestrialabundances(seeTable1).

Asdifferentratiosofhydrogenandoxygenisotopesexist,watermoleculesmayhavedifferent

molecularweights.Thesedifferencesinmassleadtodifferentreactionrateswhichthencause

isotopicfractionationi.e.duringwaterphasetransitions(ClarkandFritz,1997).

Table1:Terrestrialabundancesofstableoxygenandhydrogenisotopes(afterKloss,2008).

element isotope atomicmass naturalabundance[%]

hydrogen 1 H 1 99.985D 2 0.015

oxygen 16 O 16 99.7617 O 17 0.0418 O 18 0.2

Asdifferencesinisotopiccompositionsofvariouswatersarerelativelysmall,anisotopicratio

ofasampleisexpressedastherelativepermildeviationfromastandardisotoperatio.This

deviationisgivenasthesocalledδ-valuegiveninpermil(‰).

Ingeneral,theδ-valueiscalculatedas:

8

Equation1: !"#$%&' =)*+,-./

)*0+12+32− 1 ∗ 1000‰

Forwater isotopes, Craig (1961b) defined the StandardMeanOceanWater (SMOW) as a

reference.Accordingtotheassumptionthattheoceans,asuniformandverylargereservoirs,

are the basis of themeteorological cycle, its δ-value was defined as 0‰.When SMOW

standard,calibratedfromanoldUS-referencewater,wasexhausted,theInternationalAtomic

Energy Agency (IAEA) prepared a new standardwaterwhose isotopic composition nearly

matchestheSMOW.Thisstandard,calledVSMOW(ViennaStandardMeanOceanWater),is

theinternationallyacceptedreferencefor18Oand2Hinwaters(ClarkandFritz,1997).

Consequently,Equation1isadaptedto:

Equation2: !:;<"#$%&' = =>?

=>@ *+,-./=>?

=>@ ABCDE

− 1 ∗ 1000‰

Equation3: !F"#$%&' = GH *+,-./

GH ABCDE

− 1 ∗ 1000‰

foroxygenandhydrogen,respectively.

3.1.2 FractionationofstableisotopesIn each thermodynamic reaction, differences in reaction rates cause a disproportionate

concentrationofoneisotopeovertheother.Thisenrichmentofoneisotopeovertheotheris

calledisotopicfractionationandexpressedbythefractionationfactorα(ClarkandFritz,1997).

The factor isdefinedas the isotope ratio ina compoundAdividedby the isotope ratio in

compoundB(Hoefs,2015).

Equation4: IJKL = )M)N

Intermsofwater,fractionationoccursmainlywhileitchangesitsstate(e.g.watertovapor).

Watermoleculesconsistingoflighterisotopeshaveweakerintermolecularbondsthenthose

formedofheavier isotopesandarethereforeeasier todisintegrate.Hence,whilstawater

phasechange, lighterwatersarepreferentially turned intoastateofaggregation inwhich

9

theyarelessbonded.So,phaseswithweakintermolecularbonding(e.g.thegaseousphase)

getenrichedinlighterisotopesanddepletedinheavyisotopes(ClarkandFritz,1997).

Depending on the physicochemical reaction, the isotope partitioning occurs under either

equilibriumorkineticconditionsbothofwhicharefundamentalinthehydrologicalcycle.Due

towind shear, sea surface temperature, salinity and,most importantly, relative humidity,

evaporation of sea water imparts kinetic conditions on the fractionation. This is because

transportofwater-vaporfromtheseasurfacetotheatmosphereandviceversaisonlyequal

inbothdirectionsunderhighhumidityconditions(nearto100%relativehumidity).Theglobal

averagehumidity,however,is85%.Aslighterwatermoleculesarepreferentiallyturnedinto

thevaporphaseandtheirdiffusivityishigherthanthatofheavierisotopes,theatmospheric

water-vapor is depleted in heavy isotopes relative to the ocean basin.With temperature

increase, the fractionation factor α decreases, because lighter and heavier isotopes get

evaporatedmoreequally(Hoefs,2015).

In contrast, condensation occurs under equilibrium conditions as initial rainout/droplet

formationrequiresarelativehumidityof100%.Accordingtotheconceptdescribedabove,

heavierwatermolecules (enriched in 18O and D) favorably condense intowater droplets.

Therefore, atmospheric moisture gets further depleted in heavy isotopes with each

precipitationeventastherain isenriched inDand18O isotopesrelativetothevapor.This

ongoingdepletioninheavyisotopesiscalledRayleighdistillation(ClarkandFritz,1997),which

isalsodescribedastherainouteffectinthehydrologicalcycle.

Althoughtheprocessesofthehydrologicalcyclearerathercomplex,Craig(1961a)founda

linear correlation between 18O andD in global freshwaters, described as globalmeteoric

waterline(GMWL)withthefollowingequation:

Equation5:GMWL: !F = 8 ⋅ !:;< + 10‰ RS<T

Three decades later, Rozanski et al. (1993) refined this relationship based on global

precipitationdatafromtheGlobalNetworkforIsotopesinPrecipitation(GNIP):

Equation6: !F = 8 ±0.06 ⋅ !:;< + 10.35 ±0.65 ‰ RS<T

Theslopeof8inEquation5andEquation6iscausedbyequilibriumcondensationinthecloud

andrepresentstherelationshipbetweenthefractionationfactorsofoxygenandhydrogen.

10

Re-evaporation,asakineticprocess,leadstoaslopelowerthen8anddependsonhumidity

(Figure I). The interceptionof theGMWLwith theδDat10‰reflects theglobalaverage

relativehumidityof85%(Hoefs,2015).Dansgaard(1964)firstcharacterizedthedeuterium

excess(d-excess)inglobalprecipitationas:��

Equation7: Z'[\'"" = !F − 8 ⋅ !:;<

Thed-excessreflectsmainlythehumidityconditionsatthemoisturesource.Itincreaseswith

decreasingrelativehumidity(MerlivatandJouzel,1979,ClarkandFritz,1997).

Onamorelocalscale,boththeslope,theinterceptandthed-excesscanvarysignificantly.

These variations are then expressed in localmeteoricwater lines (LMWL)with respective

slopesandintercepts.

Ingeneral,acoolerregionhasmorenegative(lower)isotopiccomposition,whereaswarmer

regions are associated with higher δ-values (see Figure 4). This can be explained by the

aforementionedtemperaturedependencyofisotopefractionatthemoisturesource.Since

vaporpressureofHDO/H2OononehandandH218OandH2

16Oontheotherdiffersslightly

(heavierwatershavelowervaporpressure),changesinrelativehumidityduringevaporation

Figure4:Fractionationprocessesofstablewaterisotopesandtheireffectsonameteoricwater

line(SAHRA,2005).

11

alterthefractionationofoxygenandhydrogenisotopesbydifferentmagnitudes.Asaresult,

suchchangesarereflectedinthed-excess.Therefore,morearidmoisturesourcesplotabove

theGMWL. Correspondingly, humidmoisture sources plot below theGMWL (Figure 4). If

evaporation occurs within open water bodies, the residual water gets enriched in heavy

isotopes.Asshown,fractionationduringkineticprocessesisofhighermagnitudeforoxygen

isotopesthanforhydrogenisotopes.Consequently,theresidualwater isshiftedbelowthe

GMWL.Whensuchwaterscontributemoisturetoprecipitation,theslopediffersfromthatof

theGMWL(ClarkandFritz,1997).

3.1.3 EffectsonstableisotopeswithinthehydrologicalcycleInthehydrologicalcycle,theinitialmoistureisdepletedinheavyisotopeswithrespecttothe

oceans.Duringrain,heavierisotopesarepreferentiallyprecipitatedleadingtoadepletionin

heavyisotopesrelativetoinitialmoisture.Thisprocessisprogressivelyenhancedwhilethe

moistureistransportedlandwards,duetoRayleighdistillation.Hencewithincreasingdistance

tothemoistureorigin,theδ-valuesofthevapormassbecomemoreandmorenegative.This

isdescribedasthecontinentaleffect,althoughlargewaterbodieswithinthecontinentsmay

diminishtheeffect(ClarkandFritz,1997).

Dansgaard(1964)showedthatadecreaseintemperatureleadstomorenegativeδ-values.As

vapor masses, generally originated in low latitudes, are transported polewards (higher

latitudes)tocoolerregions,theybecomedepletedinheavyisotopes.Thisisdescribedasthe

latitudeeffect(Figure4).

Thetemperaturedependencyofwaterisotopefractionationalsoleadstoseasonalvariations

intheδ-values.EspeciallyatcontinentalstationswithhighannualTemperatureamplitude,

summerprecipitationisenrichedinheavyisotopescomparedtothewinterprecipitation.This

isknownastheseasonalityeffect(Figure4).

Whenvapormassesareupliftedbyorographytheycooldownunderadiabaticconditions.

Hencewithincreasingaltitudetheprecipitationhasgraduallydecreasingδ-values.Thiskind

ofRayleighdistillationofwatervaportothetopofamountainiscalledthealtitudeeffect

(ClarkandFritz,1997).

Theamounteffectdescribeschangesintheisotopiccompositionduetoevaporationduringa

precipitationevent(Dansgaard,1964).Whilehumidity is lowduring lightrain, it ishighfor

heavy rain. As described above, humidity influences the fractionation during evaporation

12

leadingtoanalterationoftheisotopicsignal.Forlightrain,theraindropsareenrichedinheavy

isotopes,andforheavyrain,signalischangedtowardsmorenegativeδ-valuesrespectively.

3.1.4 Stableisotopemeasurements

Thestableisotopiccompositionofwatersamplescanbyanalyticallydeterminedbyvarious

methods,with isotope ratiomass spectrometry (IRMS)being still themostprevalent. The

principleistheseparationofatomsandmoleculesbasedontheirmasses.Forthat,amagnetic

fieldisappliedonabeamofchargedmolecules,bendingitintoitsspectrumofmasses(Clark

andFritz,1997).

A gasmass spectrometer consists of an inlet system, an ion source, the flight tube with

installedelectro-magnetandadetectionunit(seeFigure5).Withintheionsource,aheated

tungsten-coated iridium filament ionizes a H2 or CO2 gas stream entering from the inlet

system. Subsequently, the positively charged gas molecules are accelerated by a voltage

gradient and focused into the flight tube where the ion beam is deflected by an

electromagneticfield.Duetospecificmass-to-chargeratiosoftheisotopes,thegradientof

deflectionvariesandthusthebeamissplit.Attheendoftheflighttube,severalfaradaycup

collectorsareattached,allowingforsimultaneousmeasurementsforeachioncurrent.The

signalisenhancedandexpressedasmass-to-chargeratios(ClarkandFritz,1997).

Figure5:Schemeofamassspectrometer(afterClarkandFritz(1997)).

13

AttheAWIPotsdam,aFinnigan-MATDeltaSIRMSwithdualinletsystemwasused.Atthe

front end, two equilibration units (MS Analysetechnik, Berlin) with a total capacity of 48

samplesareattached.Theequilibrationunitsarekeptinawater-shakingbathat18°C±0.01

topreventcondensation.A3-5mlaliquotofwatersampleisfilledintoaglassbottleanda

platinum-coatedstickisaddedasacatalyst.Thebottlesarescrewedontotheequilibration

unitandevacuatedbeforegasisapplied.ForδD-determination,hydrogengas(H2)isusedand

equilibratedfor180minutes.AftertheδD-measurement,CO2isappliedandequilibrated400

minutesforδ18O-analysis.Consequently,boththeδDandδ18O-valuesaremeasuredonthe

exactsamesamplealiquot(Meyeretal.,2000).

Subsequent to equilibration, the gas is transferred into the inlet system. A cooling trap

(ethanol-dryicemixture)at-78°CpreventswatervaporfromenteringtheIRMS.Bothunits

areequippedwiththe laboratorystandardNGT-1onthefirstpositionwhichservesasthe

referencegasduringtheanalysis.Eachsampleismeasured10times.

The MS output is processed with ISODAT (version 5.2) to express the δ-values as ‰-

differencesrelativetotheinternationalstandardVSMOW(Meyeretal.,2000).

If the internal error (1σ) exceeds ±0.8‰ for δD and ± 0.1‰ for δ18O, respectively, the

measurementisrepeated.Additionally,toensurequalitycontrol,sixtoeightsamplebottles

per unit are filledwith various standardwaters. The standards are selected tomatch the

expected isotopic composition of thewater samples (Meyer et al., 2000). For Siberia, the

standardwatersNGT,KARA,SEZandHDW2areused.

3.2 Analyticalmethodsforhydrochemicalwateranalysis

3.2.1 ICPOESToanalyze the cation compositionof awater sample, the ICPOEShasbeen the favorited

methodsincethemid80’s.Thetechnicisbasedupontwounits:theICP(inductive-coupled

plasma)andtheOES(opticalemissionspectrometry).IntheICPunit,asampleisionizedand

excitedelectronsareproducedwhichemitelectromagneticradiation(light)atcharacteristic

wavelengths.ThecreatedspectrumofemittedlightisthenanalyzedintheOESunit(Figure6).

TheICPunitconsistsof3quartztubes(called“torch”)surroundedbyanelectromagneticcoil.

Whenthetorchisturnedon,ahighfrequencyelectromagneticfieldisgeneratedbythecoil.

An Argon gas stream is ignited by a discharge arc of a tesla unit initiating the ionization

14

process.Asaresult,aplasmaconsistingofpositivelychargedArgonionsandfreeelectronsis

generated.Attheendofthetorchtheplasmaiscutoffbyastreamofcompressedair.

Usingaperistalticpump,asampleissuckedintoananalyticalnebulizerturningthesample

intomistwhichthenisdirectlyintroducedintotheplasma.Thehighenergyoftheplasma(up

to10000K)breaksdownthemoleculesintotheirrespectiveatomswhichthenareionized.

Within the ions electrons are excited to higher energy levels (orbitals) emitting

electromagneticwaveswhenthey jumpbacktotheirorbitaloforigin.Thesecharacteristic

wavelengthscreateaspectrumoflightwhichisanalyzedbyOESunit.

In theOESunit theemitted light is first focusedusingtoroidalmirrorsandthendiffracted

usinganechellegrating.Secondly,thelightissplitintoavisibleandaUVlightfractionusing

a Schmidt-cross disperser. Both light fractions are then analyzed by a Segmented-array

Charge-coupleddevice(SCD).Forabetterdetectionatvaryingelementconcentrationstwo

viewingperspectivesareused:theaxialandtheradialview(Nölte,2002).

AttheAlfred-Wegener-InstitutethePerkinElmerOptima8300ICPOESisused.

3.2.2 AnalysisofbicarbonateinwaterTomeasuretheamountofbicarbonateinwater,asampleistitratedwithhydrochloricacid

until it reaches a pH-value of 4.3. The amount of acid used is then calculated into the

concentrationofbicarbonateinwater.

Figure6: Schemeof the PerkinElmerOptima8300 ICPOES (taken fromPerkin Elmersupplement

material).

15

Whenacidisaddedtoa(bi-)carbonatebufferedwater,thebicarbonate(orcarbonateionsfor

alkalinewaters)reactwithdissolvedhydroniumionsformingcarbonacid.

Equation8: ]^<#_`K + ]`<#_a ⇌ ]c^<`#_ +]c<

Therefore,thepH-valueofthewaterdoesnotchangeproportionallytotheacidinput.Ata

pH-valueof4.3thefractionofbicarbonateiontodissolvedinorganiccarbon(DIC)is<1%.

DerivedfromEquation8,thestartconcentration(beforetheadditionofacid)ofbicarbonate

canbecalculatedas:

Equation9: dHe=fg = d#\hi ∙k+lm2k*+,-./

∙ SHe=fg ∙ 1000[op/r]

BicarbonateconcentrationsweremeasuredusingaMetrohm794BasicTitrino.

3.2.3 Ionexchangechromatography

To analyze the anion composition of water samples, a IC Dionex DX 320 ion exchange

chromatographwasused.

An ionexchange chromatograph (IC) consistsof amobilephase, a stationaryphaseanda

detectorunit.Themobilephaseisaneluentintowhichthesample(analyte)isinjected.The

stationaryphaseconsistsoutofapolymermatrixwithcounterchargedions.Whenthemobile

phase ispumped into the separation column, the stationaryphase retains the ionsof the

analytebasedoncoulombic (ionic) interactions.Dependingon thestrengthof thebinding

withthestationaryphase,differentionsintheanalytepasstheseparationcolumnatdifferent

speedsandhencegetseparated.Attheendofthecolumnadetectorunit(e.g.conductivity

meter)measurestheconcentrationsoftheions.InmodernICasuppressorunitsuppresses

theconductivitysignaloftheeluent.

3.2.4 pH-valuemeasurementsinwater

FordeterminationofthepH-valueofawatersample,apH-meterisusedwhichisasetofa

pH-sensitiveelectrode(normallyaglasselectrode),areferenceelectrodeandatemperature

element.Theglasselectrodeisfilledwithabufferedsolution.Whengettingincontactwitha

16

solution, water ions tend to accumulate around silicate groups resulting in a potential

(voltage). This potential is proportional to the pH-value of the solution. The reference

electrodemaintains a givenpotential at any temperature.As a result, a signal current (in

millivolt[mV])ismeasuredfromwhichthepH-valueofthesamplecanbederived.ForpH-

determinationaWTWMulti340iprobewasused.

3.2.5 Measurementofdissolvedoxygen(DO)

Formeasurementsofdissolvedoxygeninwater,anopticalsensor(WTWMulti340iprobe)

was used. In the sensor a luminophor is excited by light and its decay is measured by a

photodiode. When getting into contacted with oxygen (O2) the luminophor passes its

excitationenergytotheoxygenmoleculewhichresults inacharacteristicalterationofthe

decay.

3.3 Fieldwork

DuringlateMarchandearlyApril2013,7surfacewatersamplesofLakeBol’shoeTokoaswell

as3waterprofilesfromthecenterofLakeBol’shoeToko,thelagoonandthesmallerside

BaniaLakewerecollectedusinga1.5lUWITECwatersamplerwithintegratedtemperature

measurement.Theupper10mweresampledat0,2,5and10mwaterdepth.Forwatersat

greaterdepth,aresolutionofonesampleper10mwaschosen,toaccountforanypossible

variation within the deeper water layers. After sampling, water samples were filled into

previouslyrinsed250mlPETbottles

Additionally,oneicecoreof82cmdepthwasretrievedformtheicecoverofLakeBol’shoe

Tokoandsplitat10cmresolution.Furthermore,Snowsampleswerecollectedfromthesnow

coverofLakeBol’shoeToko.Oneprecipitationeventon2April2013wassampled.Both,ice

andsnowsamplesweremeltedinthefieldatroomtemperature.

Atthefieldcamplaboratory,conductivity,pH-valueandoxygensaturationwasdetermined

usingaWTWMulti340iprobe.Beforeeachmeasurementsession,theprobewascalibrated

according to information provided byWTW. Allmeasurementswere carried out at room

temperature(≈20°C).

Samplesforanionandcationanalyseswerefiltratedusinga0.45µmcelluloseacetatefilter.

Cationsampleswereadditionallyacidifiedwithultrapurenitricacid(65%HNO3)topH≈2,for

conservation.

17

4 Results

4.1 VariabilityoftheisotopiccompositionatLakeBol’shoeToko

To describe the variability of the isotopic composition at Lake Bol’shoe Toko (in figures

abbreviatedas“BT”),thedataissubdividedintoaspatialsetofsurfacewatersamplestaken

fromthelakeandasetofwatersamplestakenverticallyalongthewatercolumnatdifferent

sites.Additionally,one ice coreof80 cmdepthat sample sitePG2208, aswell as two ice

sampleinthesouthofLakeBol’shoeTokonearthemouthofUtukRiver,wheretheicecover

wasunexpectedlythin(<3.5cm),weretakenandanalyzedfortheirisotopiccompositionto

investigate possible fractionation processes during ice cover season. Furthermore, snow

samples(fromtheicecoveronthelakeandoneprecipitationeventduringtheexpedition)

werecollected.Intotal,6snowsamples,oneprecipitationevent,10icesamples,7surface

watersamplesand4waterprofileswithatotalof37watersampleswereanalyzed.

4.1.1 SpatialvariationoftheisotopiccompositionatBol’shoeToko

Generally,allsurfacewatersamples,takenfromthemainLakeBol’shoeToko,arewithinthe

rangeofδ18Osurface=-18.6±0.1‰(-139±1‰inδD).However,samplestakenatthesouth

of the lake near themouth of theUtuk river have a slightly heavier isotopic composition

(δ18O=-18.4‰)thansamplestakenfromthelakecenter(Figure8),whereaswatersamples

takennearthewesternshoreareisotopicallyslightlylighter(δ18O=-18.7‰).Unfortunately,

aclearstatementregardingthenorthernpartofLakeBol’shoeTokocannotbemadedueto

missingsampledata.

Comparingallsamplesinaδ18O-δD-plot(Figure7),itisevidentthatwatersamplestakenfrom

thelagoonandLakeBol’shoeTokoaresituatedclosetotheGMWL,whereaswatersofthe

sidelake“BaniaLake”areshiftedtowardsheavierisotopevaluesandlowerd-excessontothe

LMWLofYakutsk(δD = 7.57 ∗ δ:;O– 6.86(Kloss,2008)).Themeanisotopiccomposition

ofwatersamplestakeninMarchalongthewatercolumnatLakeBol’shoeToko(δ18OPG2208=

-18.2±0.2‰)isslightlyheavierthanthemeanofsurfacesamples(δ18Osurface=-18.6±0.1

‰),resultinginδ18OMarch=-18.4±0.2‰forallsamplestakenatLakeBol’shoeToko.Water

samplestakeninAugust2012,showhighervariation(seeFigure7)andhaveaslightlylighter

meanisotopiccomposition(δ18OAugust=-18.2±0.2‰)thantheMarchmeanbutsimilarto

themeanofPG2208.

18

Figure7:δ18O-δD-plotforallwatersamplesandGNIPdatafromYakutsk.GreyshadedareainplotAis

enhanced in plot B. Generally, water samples from Bol'shoe Toko (August samples in blue, March

samplesinred)andLagoon(green)aswellassnowsamplesplotwellontheGMWL,whereaswater

samplestakenfromtheBaniaLakearesituatedontheLMWLofYakutsk.

Figure8:IsotopiccompositionofsurfacewatersamplesfromLakeBol’shoeToko.

19

Incontrast,thewatersamplesofthelagoonareshiftedtowardslighterisotopiccomposition

by0.5‰(δ18Olagoon=-18.9±0.2‰).Thehighestisotopiccompositioninwaterwasmeasured

atBania Lake (δ18OBania= -16.1±0.2‰) showing clearlyanenrichment inheavy isotopes

comparedtoLakeBol’shoeTokoandthelagoon.

The isotopic composition of snow samples is depleted in heavy isotopes and range

from-30.8‰inδ18O(-227.9‰inδD)to-41.1‰inδ18O(-306.9‰inδD).Withexception

oftwosamples,allsnowsamplesarelocatedabovetheGMWL(Figure7).Viceversa,lakeice

samples are enriched in heavy isotopes (-16.1‰ in δ18O and -123.8‰ in δD),with two

outliersat-15.38‰inδ18O(-115.3‰inδD)and-14.95‰inδ18O(-111.1‰inδD,seeFigure

7)andplotbelowtheGMWL.

Table2:meanisotopiccompositionofsnow,lakeice,andwatersamplesfromtherespectivelakebasin

orwaterprofile.

Site δ18Ο[‰] standard δD[‰] standard d-excess[‰] standard

vs.VSMOW deviation vs.VSMOW deviation vs.VSMOW deviation

MeanIsotopiccompositionofsnowandlakeicesamplesatBol'shoeToko

snow -35.2 3.9 -266 30 16 4

lakeice -15.9 0.4 -122 5 6 1

MeanIsotopiccompositionofwatersamplesfromLakeBol'shoeToko BTSurface -18.6 0.1 -139 1 10 1

BTMarch2013 -18.4 0.2 -138 2 9 1

BTAugust2012 -18.2 0.3 -137 2 8 1

PG2208 -18.2 0.2 -137 1 9 1

MeanIsotopiccompositionofthelagoonandBaniaLake lagoon -18.9 0.2 -144 1 7 1

Bania -16.1 0.2 -131 1 -3 0

20

4.1.2 Isotope-depthprofilesfromLakeBol’shoeTokoanditssurroundings

4.1.2.1 SitePG2208,LakeBol’shoeTokoTwowaterprofilesweretakenfromLakeBolshoeToko.One(redsignatureinFigure9)was

takeninMarch2013duringthewintercampaignattheapproximatecenterofLakeBol’shoe

Toko(samplesitePG2208)withawaterdepthof68m.Theotherwaterprofile(bluesignature

inFigure9)wastaken inAugust2012byL.Pestryakovaatasamplesitenearthewestern

shorelinewithawaterdepthofonly37m.

TheisotopiccompositionofwatersamplestakeninMarch2013atPG2208fromLakeBolshoe

Tokoshowlittlevariabilitythroughouttheprofile(seeFigure9).Incontrasttheδ-valuesfrom

samplestakeninAugust2012showmuchlargervariations.ForMarchtheδ18Ovaluestabilizes

from10mdownwardataround-18.2‰andtheδD-valueat-136‰,whiletheratiosabove

10mupwardtotheicecovershowatrendtolighterisotopevalues,shiftedby-0.5‰inδ18O

Figure9:Isotope-depthandtemperature-depthprofilesatPG2208foroxygenandhydrogenaswellas

d-excessofmeasuredsamplesforMarch2013(red)andAugust2012(blue,samplesprovidedbyL.

Pestryakova,L.A;NEFUYakutsk)

21

and-2‰inδD,respectively.Furthermore,thereisaslightshifttowardslessnegativevalues

atthelowerendatadepthof68m.Inthisprofile,thed-excessshowsasimilarbutmirror-

invertedpicture.Forwaters>10mindepththed-excessrangesbetween8-9‰exceptat68

m,whereastheuppermostmetersshowslightlyhigherd-excessvaluesof9-10‰.InMarch,

themeanisotopiccompositionofLakeBol’shoeTokois-18.2±0.2‰inδ18O,-137±1inδD

and9±1‰ind-excess.

TheAugustdatashowsamorecomplexrelationship.Ingeneral,theisotopiccompositionfor

theuppermost10mdisplayhighervaluesbetween-18.2‰and-17.7‰forδ18Oand-136

‰ to -134‰ for δD, respectively, as compared to theMarch data. Beneath, the values

decreasetolighterisotopiccompositionuntil20mbelowwatersurface.Between20mand

30mtheyoscillatearound-18.3±0.5‰forδ18Oand-137‰±2‰forδD. Downwards,the

isotopiccompositionshiftstolighterratios,withanincreaseat36m(abovesedimentsurface).

Generally,thed-excessvaluesshowanalmostsimilardevelopment,varyingbetween6‰and

11‰.TheAugustdatahasameanisotopiccompositionof-18.2±0.3‰inδ18O,-137±2‰

inδDand8±1‰ind-excess.

Comparing both profiles, it is evident that a firstmain shift appears at a depth of 10m,

whereastwomoreshiftsareseenintheprofileforAugust.Furthermore,bothprofileshave

the same mean isotopic composition, although their isotope-depth relationships differ

strongly.

4.1.2.2 SitePG2122,“Lagoon”ThewaterprofileofPG2122,takeninMarch2013,locatedinthelagoonattheSEofthelake

shows a similar isotopic trend compared to PG2208, although the values are isotopically

lighterby0.5‰inδ18Oand8‰inδD,respectively(Figure10).AsatPG2208,near-surface

samplesδ18OandδDaredepletedinheavierisotopesbutasthebasinismuchshallower(18

mwaterdepth)theeffectislimitedtotheupper3-5m.Incontrast,thed-excessdecreases

from≈8‰to≈7‰.Themeanisotopiccompositionforthelagoonis-18.9±0.2‰inδ18O

and-114±1‰inδD,respectively.

22

4.1.2.3 Isotope-depthprofileatsitePG2131,“BaniaLake”Ashallowerprofileoftheside lake“BaniaLake”(6minwaterdepth) isenriched inheavy

isotopescomparedtothewaterprofilesofLakeBol’shoeTokoandthelagoon. Its isotopic

compositionvariesslightlybetween-16.0‰at3mand-16.3‰atthesurfaceforδ18O,and

from-132‰at3mto -130‰atthesurface inδD,accordingly (Figure11).Thed-excess

valuesshowsignificantdifferencescomparedtoPG2122andPG2208.

Figure10:Isotope-depthandtemperature-depthprofileatPG2122“Lagoon”,SEofLakeBol'shoeToko.

Generally,similartrendscomparedtothemainbasinareobservedbutlighterisotopiccomposition.

Figure11:Isotope-depthandtemperature-depthprofileforsitePG2131"BaniaLake".Samplestaken

inMarch2013

23

Theyvarybetween -3‰at thebottom(6m)and -2‰at thesurface,differingby10‰

comparedtoLakeBol’shoeToko.Themeanδ-valuesatBaniaTokoareδ18OBania=-16.1±0.2

‰andδDBania=-131±1‰.

4.2 HydrochemicalcompositionofBol’shoeToko

Forallthreebasins,thesampledwatersarewellsaturatedinO2(92-120%)withapH-value

fromneutraltoslightlyacid(6.4–7.2).Theelectricalconductivityisverylowforallwaters,

though the lagoon shows a 1.5-2 times higher conductivity (64.5 µS/cm) than the Lake

Bol’shoe-Toko(29.1–42.9µS/cm,35.0µS/cminaverage)andtheBaniaLake(40.4µS/cm).

Allbasinswereshowthermalstratification,withfouridentifiedlayersfortheBol’shoeToko

mainbasin (with thermoclinesataround5,20and50mwaterdepth), two layers for the

lagoon(thermoclineat5m)andthreefortheBaniaLake(thermoclinesat3and6m),though

thesearejustestimatedthermoclinesbasedontemperatureshiftsinthemeasureddata,but

thesamplingresolutionistoolowtogiveexactthermoclinedepths.

Figure12:Piper(1944)Plotforallwatersamplesofdifferentsamplesites.Allsamplesaredetermined

asCa-Mg-HCO3-Typewater

24

Thehydrochemicalcompositionsofall threesamplesites (LakeBol’shoeToko, lagoonand

BaniaLake)havesimilarvalues,visualizedinaPiperplot(Figure12)allsamplesplotroughly

within60:35:15±5%(Ca2+:Mg2+:K++Na+)ofthecationcompositiontriangle.

Asimilarpatternisshownfortheanioncomposition.Here,HCO3- isdominantforallbasins

butthereisanotabledifferencecomparingthemainbasinofLakeBol’shoeTokowiththe

lagoonandtheside lakeBaniaLake.Whereasthe latterplotnearlyat100%HCO3- (green

diamonds and orange squares in Figure 12), samples taken from Lake Bol’shoe Toko (red

triangles)haveaminorcontentofsulfateandchloride(HCO3- /SO{cK/Cl

-=80/17/3[%]).

The compositediamondplot clarifies that thebasins only vary in their anion composition

thoughallsamplescanbeclassifiedasCa-Mg-HCO3-typewaters(accordingtoPiper,1944).

Regardingminorelements,innearlyallsamplestracesofaluminum(Al)andiron(Fe)have

beenfound.Concentrationsofmanganese(Mn)weremeasuredinwatersamplesclosetothe

bottom(inallbasins).Therewasnoevidenceforsignificantconcentrationsofenvironmental

relevantelements(Pb,Cr,V,Co,Ni,Cu).

For Lake Bol’shoe Toko, the highest concentrations of Aluminum (Al), Silicon (Si) and

Strontium (Sr) concentrations were measured in surface samples with decreasing

concentrationswithdepth,exceptforaconcentrationincreaseabovethesedimentsurface.

Asimilarpictureisdrawnforthelagoon,thoughhere,incomparisonwiththemainbasinof

LakeBol’shoeToko,lessAl(50%lower)buthigheramountsofSi(1.5timeshigher)andSr(3

–3.5timeshigher)weremeasured.

ForBaniaLake,itishardtoinferageneraltrend,regardingthelowsampleresolution,butthe

concentration of Al in waters is comparable to waters taken from the lagoon and its Sr

concentration comparable to the once measured at Lake Bol’shoe Toko. Silicon

concentrationsareevenlowerthanthosemeasuredatLakeBol’shoeToko.

Theconcentrationsofsulfate(SO4c-)followsthetrendofAl(highestconcentrationatBol’shoe

Toko(2.4mg/l),lowconcentrationinthelagoon(0.5mg/l)andBaniaLake(0.4mg/l))andthe

concentrations of nitrate (NO3- ) themirror-inverted trend of Sr (higher concentrations in

watersfromBol’shoeTokoandBaniaLake(both≈0.8mg/l)incomparisonwithwatersamples

fromthelagoon(0.3mg/l)).Therewasnophosphorusfound.

25

5 Discussion

InthischaptertheresultsofthesampledatafromLakeBol’shoeTokoareinterpretedand

discussed.Firstly,possiblewaterandprecipitationsourcesofthestudyareaareexamined,by

comparingprecipitationandsnowdatatakenduringthefieldcampaignwithdataofYakutsk

fromtheGlobalNetworkof Isotopes inPrecipitation (GNIP)andfromKloss (2008).Spatial

variations in the isotopic and hydrochemical composition at Lake Bol’shoe Toko and its

surroundings are discussed with regard to the geomorphological and geological setting.

Furthermore,changesintheisotopiccompositionwithdepthareinterpretedwithrespectto

seasonallakewaterstratificationandfractionationprocesses.Lastly,theisotopiccomposition

ofLakeBol’shoeTokoisdiscussedintheregionalcontext,comparingitwithtwootherlakes

alongawest-easttransectofsamelatitude.

5.1 WaterandprecipitationsourcesforLakeBol’shoeToko

TheisotopicsignalmeasuredinCentralandEastSiberianprecipitationindicatesacomposite

ofmoisturesources(Kuritaetal.,2004).Theprecipitationispredominantlyofwesternorigin

(Shahgedanova,2002),hencemoisturemasseshavebeentransportedafardistanceandare

thereforedepletedinheavyisotopesduetoacombinationoflatitudeeffectandcontinental

effect,thesocalledRayleighdistillation(Rozanskietal.,1993,Kuritaetal.,2004).However,

secondarymoisturesourceshavebeenreportedtobetheArcticOceanintheNorthandthe

Sea of Okhotsk in the East (Kurita, 2003, Kloss, 2008). Additionally, air mass movement

towardsthestudysiteformtheSeaofOkhotskislikely,asthedistanceisonly300kmandthe

mountainousrangedoesnotexceed1500m.Thiscouldcontributetothehigherannualmean

precipitationatLakeBol’shoeToko(452mm/year)comparedtoYakutsk(250mm/year).Long-

termmeansurfacewindsindicatethatduringwinter,suchtransportofairmassesfromthe

EastispreventedbytheSiberiananticyclone,whereasduringsummermonths(JunetoJuly)

westwardtransportofairandmoisturefromtheSeaofOkhotsklandinwardsoccurs(Kurita,

2003, Leeetal.,2003).Although, thispatternofprecipitation is stillunclear (Kuritaetal.,

2004),itmightberesponsibleforthehighrangeinannualprecipitation(≈232to≈640mm,

Konstantinov (2000), NOAA record of Toko RS (1960-2015). Nonetheless, there is a

pronouncedseasonalsignalwithintheisotopiccompositionofprecipitationwithisotopically

lightsnowfallinwinterandheavierisotopiccompositioninsummer,thatcannotbeexplained

entirelybyseasonaltemperaturevariation(Kuritaetal.,2004).Thisobservationissupported

26

bymodelscalculatingtheisotopiccompositioninprecipitation(BowenandWilkinson,2002,

Bowen and Revenaugh, 2003, Bowen et al., 2005). The online isotopes in precipitation

calculator(OIPC)predictsameanannualδ18Osignalof-14.9±0.8‰and-113±6‰inδD,

respectively,forLakeBol’shoeToko(seeFigure13).However,modelstendtounderestimate

isotopicdepletionduetoRayleighdistillationofprecipitationoverCentralandEastSiberia

(Butzin et al., 2014). When checking the model’s consistency versus GNIP data taken at

Yakutsk,thisbecomesevident.TheOIPCcalculatesanannualmeanof-14.5‰inδ18Oand-

113‰inδD,respectively,whereasannualmeansbasedondailyprecipitationare-20‰in

δ18Oand -158‰ inδD. Taking these shortcomings into consideration,models’ calculated

annualmeaniscomparabletothemeanisotopiccompositionofLakeBol’shoeToko(-18.3±

0.2‰inδ18O),supportingthehypothesisthatBol’shoeToko’sisotopicsignalisdirectlylink

toprecipitation.

Additionally,Bol’shoeToko’smaininflow,theUtukRiver,springsintheStanovoimountains

(peaks up to 2900 m) discharging meltwater and precipitation into the lake. As winter

precipitationisisotopicallylighterduetocoldertemperatureduringinitialmoistureformation

(seasonalityeffect,e.g.Dansgaard,1964,Rozanskietal.,1993),theresultingmeltwatersare

isotopicallydepleted.Furthermore,rainfallinthemountainsisadditionallydepletedinheavy

isotopesduetothealtitudeeffect.CalculationsfromOIPCfortheoriginregionofUtukRiver1

1(coordinates:55.888049°N,130.453781°W,1944maltitude,samplepointpickedbytracingtheUtukrivervia

satellitepictures(GoogleEarth)).

Figure13:AnnualmeanδDandδ18O inprecipitationpatterns (Isoscapes) forNorthAsia. Redstar

showsstudysite(adoptedafterWestetal.,2010).

27

were-16.9±1.0‰inδ18Oand-128±8‰inδD,respectively,indicatingadepletionof≈2‰

inδ18O, compared to thepredication for LakeBol’shoeToko (δ18O -14.9±0.8‰),due to

higheraltitudes(althoughtheRayleighdistillationisstillunderestimate).Asaresultofthis

isotopicdepletionduetohigheraltitudes,riverrun-offintoLakeBol’shoeTokoleadstolighter

isotopiccompositionofthelakewater.

AtLakeBol’shoeToko,severalsamplesofsnowcoveringthelakeiceweresampledandone

precipitationevent (02April 2013)was captured.Themean isotopic compositionof these

snow sample was -35.2 ± 3.9‰ in δ18O and -266 ± 30‰ in δD, respectively, which is

comparable to winter precipitation measured at Yakutsk. Therefore, a similar moisture

transportationpathandconditionslikeoriginovertheNorthAtlanticwithisotopicdepletion

overwesternSiberiaandcoldtemperaturecanbeassumed.Themeand-excessofsnowof

16±4‰indicatesaridandcoldconditionsatthemoisturesource.Thehighd-excessis in

goodagreementwithsnowpackanalysisineasternSiberiacarriedoutbyKuritaetal.(2005).

Additionally,highd-excessesforthenorthernhemisphereandforbothsuggestedmoisture

sources(NorthAtlanticandSeaofOkhotsk)werepredictedbyPfahlandSodemann(2014)

duringwintermonths(DecembertoFebruary).

Figure14:HYSPLITbacktrajectoryfrequenciespriortoboth6-dayprecipitationeventsinAugust2012

(06-08.08.2012 (A), 17.-22.08.2012 (B)) and to the precipitation event 1-3 April 2013 (C). A new

trajectorywasstartedeach6handrunfor120h.Frequencycalculatebasedona2x2degreegrid.

Backtrajectoryfrequenciesindicatevariousmoisturesourcesforthe06-08.08.2012(A),whereasfor

17.-22.08.2012(B)and1-3April2013(C)apredominantlywesternoriginisdisplayed.

28

UsingNOAAHYSPLIT(Steinetal.,2015,Rolph,2016),backwardstrajectoryfrequenciesfor

120hpriortotheprecipitationeventsonthe2April2013duringtheMarchcampaignaswell

as for two precipitation events in August 2012weremodelled.Whereas a predominantly

westernoriginoftheairmassfortheprecipitationeventinApril2013(seeCinFigure14)and

fortheeventduring17to22August2012(seeBinFigure14)issuggested,themodelindicates

variousairmassoriginsduringthe06and08August2012(seeAinFigure14).Thissupports

theassumptionthatmoistureduringsummermaybebroughtfromvarioussourceregionsto

Bol’shoe Toko. However, the branches of southern origin in A and B (Figure 14) can be

excludedasmoisturepathways,becauseLakeBol’shoeTokoisshieldedintheSouthbythe

Stanovoymountainrange.

Inconclusion,duetolackingprecipitationdataoverSiberia,aprimarymoisturesourcecannot

beidentifiedclearly.Bothmodelledsummerandmeasuredwinter(snow)precipitationdata

indicate a composite of source moisture. However, literature reports primarily westerly

influences,meaningthateasterlyandnortherlysourcesmightbeofsubordinatepriority.

5.2 TheisotopicsignalofLakeBol’shoeTokoanditsspatialvariations

Based on the surfacewaters, there is no evidence for significant spatial variations in the

isotopiccompositionforLakeBol’shoeToko.However,twosamplepointsneartheshorein

theSouthofLakeBol’shoeTokoshowslightlyheavierisotopiccompositions.Thismightbe

duetomixed-inisotopicsignalsofsmallercreeksrunningintothelake.

ThemeanisotopiccompositionofthewaterprofileatPG2208(δ18OPG2208=-18.2±0.2‰)is

slightlyheavierthanthesurfacesamples(δ18Osurface=-18.6±0.1‰)butthisisexplainable

duetoisotopicfractionationduringiceformation.Heavierisotopeswillpreferablybeturned

intoice,resultinginadepletionofheavyisotopesinthesurfacewaterlayer.Forallsamples,

themeanvalueδ18Omeanis18.4±0.2‰,althoughδ18OPG2208mightbemorerepresentableas

fractionation influence is limited to the uppermost 10 m of the water column and Lake

Bol’shoeTokoisdeeperthan10mforthemajorityofitsextension.

The threesampledbasins,however,haveadistinct isotopicsignal (Figure7).Theheaviest

(highest) isotopic compositionwasmeasuredat themuch shallowerand smaller side lake

“Bania Lake” (δ18OBania = -16.1 ± 0.2 ‰), whereas the lowest isotopic composition was

measuredatthelagoon(δ18Olagoon=-18.9±0.2‰).Additionally,whereaswaterstakenfrom

thelagoonandLakeBol’shoeTokoaresituatedclosetotheGMWL,waterfromBaniaLakeis

29

shifted underneath the GMWL and correlates better with the local meteoric water line

(LMWL) of Yakutsk (see Figure 7). This is indicative that Bania Lake may be affected by

evaporativeenrichmentduringsummer,while the lagoonandBol’shoeTokoarenotorat

leastnottoasignificantdegree.

Thelowd-excessBaniaof-3‰atBaniaLakesupportsthisassumption,sincelighterisotopes

arepreferentiallyevaporated.Asaresult,shallowbasinsgetenrichedinheavyisotopesdue

to evaporation which decreases the d-excess of the residue water. Consequently, during

summer, the initial isotopically depleted melt-water feeding Bania Lake gets enriched as

lighterwatersarepreferablyturnedintovapor.Thisenrichmentisenhancedduetotheshape

of Bania Lake (shallow but relatively extensive basin). These evaporative enrichments are

typicalforclosed-systemlakes(e.g.Ichiyanagietal.,2003,Mayretal.,2007,Kostrovaetal.,

2013).

Incontrast,thelagoonisisotopicallyslightlylighter(δ18Olagoon=-18.9±0.2‰)thanBol’shoe

Toko’smainbasin.Itsmeanisotopiccompositionshowsasmalldifferenceof0.5‰inδ18O

and6‰inδDcomparedtoLakeBol’shoeToko.Anunnamedriverwhichdischargesintothe

lagoonoriginatesfromasmallerlakeca.5kmsoutheastofLakeBol’shoeToko.Therefore,

dischargeintothelagoonishighestduringmeltingseason,bringingisotopicallylighterwaters

into the lagoon. Due to its connection to Lake Bol’shoe Toko, the lagoon then acts like a

through-flow system lake furtheroutflowingwater into LakeBol’shoeToko,which in turn

levelstheirisotopicsignaltosomedegree.

AlthoughtherewasnoevidenceforevaporationeffectsfoundforLakeBol’shoeTokointhe

presentsystem,thismighthavebeendifferentinthepast.Löffler(2016)reportedvaryinglake

waterlevelsoverthelast19,500yearsBP.Higherlakewaterlevelthanpresentwouldresult

in the flooding of the relatively shallow bank in the eastern part of Lake Bol’shoe Toko,

increasingtheareaofshallowwaterofthelake.Furthermore,itwouldresultinaconnection

betweenBaniaLakeandLakeBol’shoeToko.Suchaconnectionwasalsohypothesizedby

Weniger (2016)duringtheEarlyHoloceneandMid-Holocene.For thisepoch,Chironomids

record,derived fromasedimentcore fromBaniaLake, indicated4-5mhigherwater level

compared to present Bania Lake, as well as colder water temperatures and oligotrophic

conditions similar to present Lake Bol’shoe Toko. With the onset of the Late Holocene,

loweringwaterlevelsledtothepresentseparationofbothlakes.Additionally,thisareawas

reported as a lake terrace (Kornilov, 1962, Konstantinov, 2000) which supports this

30

hypothesis. An increase in shallowwater areamight have increase evaporation and thus

leadingtoenrichment inheavy isotopesandhencehigherδ18O-values,at least forsurface

waters in this specific areas.However, Löffler (2016) andWeniger (2016), both suggested

higherinflowofcoldmeltwaterbytheUtukriverduetoglacialretreatduringtheEarlyand

Mid-Holocene.Thus,thedischargeofisotopicallydepletedwatermighthavebeenhigherthan

ofthepresentsystem,opposingtheeffectofpossibleenhancedevaporativeenrichment.In

fact,ifanincreaseinwaterdischargefromtheStanovoimountainswasthemaincontributor

toawaterlevelriseof4-5mduringEarlyandMid-Holocene(assuggestedbyWeniger(2016)),

themeanisotopiccompositionofLakeBol’shoeTokomayhavebeenlowerthanmeasuredin

thepresentlake.

5.3 Isotope-depthrelationshipatLakeBolshoeToko

Thetrendofallwinterwaterdepthprofilestolighterisotopiccompositionintheuppermost

partisdirectlyrelatedtoisotopicfractionationthataccompaniesicecoverformation.Asice

is a state of aggregation with higher intermolecular bonding, heavier isotopes are

preferentiallyturnedintoiceleavingtheuppermostwaterlayer(fromwhichtheiceisformed)

isotopicallydepleted.Mixtureof thedepletedwaterswith therestof thewatercolumn is

Figure15: Isotope-depth profiles forbothwater (red)and lake ice (turquoise)at site PG2208, Lake

Bol’shoeTokotakeninMarch2013.Negativedepthvaluesdisplaythethicknessoftheicecoverinm.

31

suppressed by temperature stratification under the icewhich is distinct for Lake Bol’shoe

Toko. A temperature increase from 2m to 5 m was observed which correlates with the

maximumshiftinδ18O(0.35‰)andδD(1.9‰).Forwatersbelowtheupperwaterlayer(10

mforLakeBol’shoeToko) the isotopesignal isuniform indicatingaverywellmixedwater

column with no isotopic stratification (Figure 15). This indicates that after thermal

stratificationthelake’swaterisotopiccompositionisnotalteredexceptduringiceformation.

FortheAugust2012data,thereisamorecomplexisotope-depthrelationship.Althoughthe

watersmeanisotopiccompositionof-18.2±0.3‰inδ18Oand-137±2‰inδD,respectively,

isthesameasobservedforwaterstakeninMarch2013,theindividualisotopiccomposition

showsazig-zagpattern(Figure9).Asimilarmeanisotopiccompositionindicatesevaporation

hasnotastrongeffectandthereforethereseemstobenostrongseasonalchange.Thisis

typicalforthrough-flowlakes(Mayretal.,2007).However,thezig-zagpatternisunusualfor

thiskind.Firstly,theuppermost10mareisotopicallyheavierthanthewaterbelow.Although

duringevaporation lighter isotopesarepreferentially turned intowater vapor, leaving the

remainingwaterenrichedinheavyisotopes,thisprocesscanbeexcluded.Evaporationasa

kineticprocess isdependedone.g. relativehumidity,windshearandsurfacetemperature

anditssignalismarkedincharacteristicevaporationlineswhenplottedinaδ18O-δDdiagram.

Thismeansthattheuppermostwatersampleswouldbesituatedalongalinebelowtheglobal

meteoricwaterline(GMWL,δD=8*δ18O+10)withaslope<8.IntheAugustdata,there

werenosuchevaporationlinesfound.Incontrast,themeasuredδ18OisclosetotheGMWL

indicating an unaltered precipitation signal (see Figure 9). Additionally, evaporative

enrichmentduringsummerispronouncedforwellthermalstratifiedlakes(dimictic)where

mixingisprevented(Mayretal.,2007).SuchthermalstratificationisweakatleastinAugust

2012indicatingacoldpolymicticlake.

Meteorologicaldatafromthenearbyweatherstation(TokoRS,10kmnorthward)recorded

heavyrainfallforAugust2012.Two6day-longprecipitationeventsaccountedformorerain

thentheAugustlong-termmean.Intotal,August2012precipitationwas25mmabovethe

long term mean (83 mm). Such precipitation events could cause temporary isotopic

stratificationoravariationintheisotopicsignalthroughoutthewatercolumn.Precipitation

insummerhasaheavierisotopiccompositionthantheannualmean.Additionally,summer

32

rainfallisassumedlywarmerthanthewaterbodyofLakeBol’shoeToko,asitisfedbycold

riverrunofffromthemountains.

Thus,thethermaldifferencesleadtodifferentwaterlayers,carryingslightlydifferentisotopic

signals. Due to ongoing mixing, these variations are then evened. In conclusion, such

variations in the isotopic composition throughout theAugust profile aremore a temporal

phenomenonandnotcharacteristicforLakeBol’shoeToko.

5.4 Discussionofthehydrochemicalcomposition

Themajorioncomposition(Figure12)aswellasthelowconductivityofLakeBol’shoeToko,

BaniaLakeandthelagoon,pointtowardsalakesystemwithwatersupplymainlyfromsurface

run-offandatmosphericprecipitationandfreshwaterconditions.Furthermore,itindicates

rockdominanceofigneousrocktype,especiallyforLakeBol’shoeToko(Wetzel,2001).

ThemajorcationcompositionofCa»Mg>Na>K,however,contraststhisassumption,since

magnesiumconcentrationsarehigherthansodiumconcentrationsforallsamples.Hence,a

composite salinity source of igneous rocks overwritten by weathering of

calcareous/sedimentary rocks is suggested. This is supportedby the anion compositionof

HCO3»SO4>ClatleastforLakeBol’shoeToko,sincesulfateinfluxismainlyduetoweathering

ofrocksandsoils.

Incontrast,sulfateconcentrationatthelagoonandBaniaLakearelowerthanatLakeBol’shoe

TokoandtheanioncompositionisshiftedtowardsHCO3»Cl≥SO4,thusindicatingagreater

influenceofacalcareousandsalinitysource.Infact,inthelagoonthereisanotableoverall

increase of Ca, Mg and HCO3 concentrations resulting in higher salinity/conductivity.

ConductivityandCa,MgandHCO3concentrationsofBaniaLake,however,showonlyaminor

differenceincomparisonwithLakeBol’shoeTokowater.

AforementioneddifferencesinCa,Mg,SO4andbicarbonatecanbeeithercausedbychanges

ofacidicprecipitation(e.g.duetohigherimpactoftheadjacentcoalminingactivity)inthe

correspondingwatersourceregionsorchangesofthecorrespondingsourceelementsinthe

bedrockorsoil,respectively(mineralcomposition,e.g.calcite,pyriteintherock).Forthearea

ofLakeBol’shoeToko,sameacidicprecipitation isassumed,sinceriversrunning intoboth

lagoon and Bol’shoe Toko are not of significant length. So, both drainage areas (for Lake

Bol’shoeTokoandthelagoon,respectively)likelydifferintheirabundanceofsulfuricminerals

pronetoweathering.Thisisanindicationforchangesofrocktypeforthedrainageareas.

33

Consequently, based on the major ion composition, water supply from slightly different

sourcesforeachbasinissuggested.

These differences are also reflected within the concentration of minor elements. Nitrate

concentrationofallthreesamplebasinsarewithintheglobalrangeforunpollutedfreshwater

(0.1-1mg/l).However,concentrationsofnitrate inthe lagoonwere≈50%lower(0.3mg/l)

thenmeasuredforLakeBol’shoeTokoandtheBaniaLake(≈0.8mg/l).Inconjunctionwiththe

non-presenceofanyphosphorusasadditionalnutrient,nitrateconcentrationsbelow0.3mg/l

havesignificantimpactonalgaegrowth(Wetzel,2001).

ThehigherAluminiumconcentrationinwatersofLakeBol’shoeTokosupporttheigneousrock

influenceofsourcewater,whereasthedistributionofsiliconinwater(primarilyoccurringas

dissolvedsilicate),however,iscontradictiveatfirstglance.Theenrichmentinthelagoondue

tostronger influxof silicon isunlikely, sincesourcesof siliconaremainly silicateminerals.

Nonetheless,therelativeenrichmentofsiliconinthelagoonwatermaybeduetoinhibited

uptake by e.g. diatoms, higher recycling rates of silicon from the sediments and/or prior

enrichment in thepond feeding the lagoon.Lastly,higher strontiumconcentrationsat the

lagoon thanmeasuredat LakeBol’shoeTokoorBaniaLakearecorrespondingwithhigher

calcium and bicarbonate concentration, since strontium behaves geochemically similar to

calciumandthereforeiscommonlyassociatedwithcalcite(e.g.Odum,1951,Faure,1977).

Insummary,theioniccompositionofwatersatLakeBol’shoeToko,lagoonandBaniaLake

reflect the geomorphologic and geologic setting of the study area. The Utuk river which

discharges intoLakeBol’shoeTokosprings inthepredominantlymaficStanovoimountains

andthenrunsoverCretaceousandJurassicsedimentaryrockshenceuptakesbothsignalsdue

toweathering. In contrast, the unnamed river running into the lagoon carries no igneous

signatures.But,sincesedimentarydepositsaremorevulnerabletoweatheringthanigneous

rocks,therelativeiondischargeoftheunnamedriverintothelagoonishigherthanthatUtuk

river.Lastly,BaniaLake’sioncompositionsupportstheassumptionofpredominantinputof

atmosphericwaterandresultingnearbysurfacewaterdischarge.Asaresult,waterfromBania

Lake shows slightly higher Ca,Mg, HCO3 concentrations than Bol’shoe Toko but lack the

igneoussignalofSO4,AlandSi.Additionally,highersoil-waterinteractionbeforerunninginto

thecorrespondinglakebasinsisreflectedintheironandmanganesesignatureofBaniaLake

and lagoonwater, as iron andmanganese input is generally causedby anoxicweathering

conditionsofsoils(Wetzel,2001).

34

Generally, the uniformity of the ion composition along thewater column and spatially in

surfacewaterswithintheirrespectivelysamplebasinshintstowardsawell-mixedwaterbody

inwintertime.Therelativeenrichmentofionsinthesurfacelayercomparedtowatertaken

fromdeeperwaterlayers,whichisreflectedforallbasins,isaneffectoficecoverformation

(leavingsaltsasresidueinthesurfacewaterlayer).

Therewasnoevidenceinthehydrochemicaldataforanimpactonthelakeecosystemdueto

enhancedcoalminingactivity intheadjunctarea,aspresumedbyKonstantinov(2000),as

sulfate,nitrateandotherrelatedionsconcentrationsarebeloworwithinglobalaveragefor

unpollutedfreshwaters.

Overall,thehydrochemistrydatacorrespondswellwiththeisotopeanalysisandvice-versa.

Basedonbothdatasets,LakeBol’shoeTokoandthe lagooncanbecharacterizedasacold

polymictic(stratifiedinwinter,weakornon-stratifiedinsummer),oligotrophic,openthrough-

flowlakesystem.Incontrast,BaniaLakeisaclosedsystemlake,effectedbyevaporationin

summerand,basedonloweroxygenconcentrations(comparedtoLakeBol’shoeToko)and

itsshape,assumedlydimicticandeutrophic.

5.5 LakeBol’shoeTokoinregionalcomparison

TocompareLakeBol’shoeTokowith the regional settingofSiberian lakes, twopreviously

investigatedlakesofcomparableclimaticandgeologicsettingwerechosen:Two-Yurtslake

onKamchatkaPeninsula(Meyeretal.,2015)andLakeKotokel(Kostrovaetal.,2013),aside

lakeofLakeBaikal.

Although all three lakes are of similar latitude, they show significant differences in their

isotopiccompositionsanditslinktoprecipitation.

Bol’shoe Toko and Two-Yurts are isotopically non-stratified and well-mixed. Evaporative

enrichmentduringsummerisnotpresent.Additionally,bothlakeshavelowconductivitiesin

common.Primarilyresponsiblearetheirsimilarsettings,asbothareelongatedthrough-flow

lake system in amountainous region. Two-Yurts Lake, aswell as Lake Bol’shoe Toko, are

predominantly fedbyriverrun-offandprecipitationresulting inaclose linkof the isotope

signal between lake water and precipitation. Their waters are situated along the GMWL.

However,LakeBol’shoeTokois isotopicallylighterthanTwo-YurtsLake,possiblyduetoits

higher altitude (Bol’shoe Toko: 904 m a.s.l.; Two-Yurts Lake: 275 m a.s.l.) and different

pathwaysofmoisture.Two-Yurtslakehasamorecostal/maritimeinfluencedclimate(Meyer

35

etal.,2015),whereasatLakeBol’shoeTokocontinentalclimateisprevailing(Shahgedanova,

2002).

In contrast, Lake Kotokel represents partly a closed-system lakewith notable evaporative

enrichment. ItswatersareshiftedbelowtheGMWL(Kostrovaetal.,2013).However,Lake

Bol’shoeTokoandLakeKotokelsharesimilarsourcewaterdynamics,sincebothlakes(aswell

asTwo-Yurtslake)aremostlyprecipitationandmeltwaterinfluenced.Theestimatedoriginal

meteoricwaterpriortoevaporationforLakeKotokelis≈-18.5‰inδ18O(Kostrovaetal.,2013)

whichiscomparabletoLakeBol’shoeTokoδ18Omeanof18.4±0.2‰,indicatingsimilareffects

ontheisotopiccompositionofmoisture.Thisisnotsurprising,sincebothlakesgetdischarge

fromamountainousregion(Kostrovaetal.,2013).

Insummary,LakeBol’shoeTokoshowssimilarcharacteristicsofwatersourcedynamicsas

LakeKotokel(demititsevaporativeenrichment)andTwo-YurtsLake.Thereisgoodcorrelation

between lake water isotopes and isotopes in precipitation, especially for the two open

through-flowlakesystems.

36

6 Conclusions

ThevariabilityofisotopicandhydrochemicalcompositionatLakeBol’shoeTokowasassessed

usingstablewaterisotopeandhydrochemicalanalysis.Theresultswerethencomparedwith

thegeomorphologicalandgeologicalsettingaswellasregionaldata(GNIP,Two-YurtsLake

andLakeKotokel).

PrecipitationatLakeBol’shoeTokoisassumedlyofwesterlyoriginwithsubordinatesources

over the Arctic Ocean and Sea of Okhotsk. Due to its continental setting, the isotopic

compositionofprecipitationisdepletedinheavyisotopesandhasastrongseasonalsignal.

However,thisseasonalityisnotreflectedintheisotopiccompositionofthelake,duetolarge

amounts of riverine input of meltwater and a well-mixed water body. Furthermore, the

isotopic compositions of Lake Bol’shoe Toko (δ18OBolshoe= -18.2 ± 0.2‰) and the lagoon

(δ18OBolshoe= -18.9 ± 0.2 ‰) correspond with the GMWL and do not show evaporative

enrichment. Both isotopic and hydrochemical data indicate atmospheric precipitation and

meltwaterasthemainwatersource.Accordingly,δ18OBolshoeisdirectlylinkedtoδ18Oprecipitation.

The water of Lake Bol’shoe Toko is well mixed and does not show significant isotopic

stratification.Fractionationonlyaffectstheisotopiccompositionofthesurfacewaterduring

lakeice-coverformationwherethermalstratificationpreventsmixing.

Overall,LakeBol’shoeToko,lagoonandBaniaLakeshowunpollutedfreshwaterconditions

withlowconductivityandcorrespondingionconcentrationsbelowtheglobalaverage.They

arewellsaturatedinO2,neutraltoslightlyacidicandshowedthermalstratificationinwinter.

AlthoughallwaterscanbecharacterizedasCa-Mg-HCO3-Typewater,thethree lakebasins

showdistinctvariationswithregardtotheirmajorandminorioncomposition.Thelagoonhas

lownutrientconcentrations,potentiallyinhibitingalgaegrowth.Thesevariationsaredirectly

linkedtodifferencesinwaterorigin.

In summary, LakeBol’shoeToko is a coldpolymictic, oligotrophic, open through-flow lake

system.Itisanundisturbedecosystem,wellsuitedforpaleoclimateresearch.

37

7 Outlook

In further investigations onBol’shoe Toko, the isotopic composition of biogenic silicate in

diatomsinsedimentsurfacesampleswillbeanalyzed(inprocess)andwater/diatomisotopic

fractionation to be determined. This combined data can then be used for paleoclimate

reconstructionbasedonδ18Odiatomsinlongsedimentcores,sinceδ18Odiatomsisaproxyoflake

waterconditions(e.g.temperature)whichareinturnlinkedtothelocalandregionalclimate

patterns.SedimentcoresofthelagoonandBaniaLakeshouldbecomparedwithsediments

ofLakeBol’shoeTokotogetabetterunderstandingofpossiblechangesinlakewaterlevel

and lakeexpanse. Future investigation shouldalsoaccount for changes inδ18Owaterdue to

glacial advances and retreats, since large amounts of meltwater discharge may alter the

isotopiccompositionofthelakewaterandhenceinfluencingthelinkbetweenisotopesinlake

waterandprecipitation.

Furthermore, sedimentological data and bioindicators (e.g. diatoms) suggest that the

northernpartisinfluencedbyrunofffromthemoraine.Butmoreindicators(suchasisotopes

andhydrochemicaldataofrecentwatersamples)areneededtogetabetterknowledgeabout

themechanisms.Additionalwatersamplesfrominflowandoutflowaswellasaspatialsetof

summersurfacewatersamplesoflakeBol’shoeTokowouldhelpacquiringbetterinformation

aboutseasonaleffectsonwaterconditionsandtheisotopiccomposition.

38

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i

Appendix

Table3:IsotopiccompositionofsnowandicesamplestakenatLakeBol’shoeToko.

Site δ18Ο[‰]vs. δD[‰]vs. d-excess[‰]vs.

VSMOW VSMOW VSMOW

Snowcoversamplesfromvariouslocations PG2206,0-33cm -33.45 -257.0 10.5

PG2116-X13 -35.86 -268.7 18.2

PG2116-X16 -37.95 -285.2 18.4

PG2122,0-21cm -36.86 -283.5 11.5

PG2122,21-31cm -41.14 -306.9 22.2

PG2122,31-47cm -30.43 -227.9 15.5

Precipitation,collectedduringsnowfallon02April2013

BTSnow02.04.2013 -30.81 -229.4 17.0

Surfaceicesamples PG2116-X13 -15.38 -115.3 7.8

PG2116-X16 -14.95 -111.1 8.5

PG2208,icecore,numbersindicatedepthincm 0-10 -16.52 -126.7 5.5

10-20 -16.00 -123.7 4.3

20-30 -16.27 -125.2 5.0

30-40 -16.05 -123.2 5.2

40-50 -16.09 -123.7 5.0

50-60 -15.97 -123.1 4.7

60-70 -15.84 -122.3 4.5

70-82 -16.00 -122.3 5.7

ii

Table4:IsotopeandhydrochemistrydataforallwatersamplestakeninMarch2013(continuesonpageXI).Sampledepth δ18Ο[‰]vs. δD[‰]vs. d-excess[‰]vs. Temperature Oxygencontent Conductivity pH Ca2+ Mg2+ Na+

[m] VSMOW VSMOW VSMOW [°C] [%] [µS/cm] [mg/l] [mg/l] [mg/l]

PG2208,waterdepthprofileofLakeBol'shoeToko 0 -18.5 -138.5 9.4 0.5 110.9 35.1 6.8 4.73 1.09 0.782 -18.56 -138.4 10 0.5 119.9 35.6 7.0 4.69 1.07 0.725 -18.21 -136.5 9.2 1.5 110.4 32.1 7.1 4.10 0.90 0.6410 -18.1 -136.5 8.3 1.8 108.9 29.5 7.0 3.82 0.86 0.5520 -18.11 -136.1 8.8 2.5 111.6 31.2 7.0 3.84 0.84 0.6130 -18.11 -136.6 8.2 2.5 108.1 29.7 7.0 3.89 0.87 0.5740 -18.14 -136.1 9 2.5 111.5 29.1 6.9 3.81 0.84 0.6350 -18.12 -136.3 8.7 4 102.4 29.9 7.0 3.71 0.84 0.6360 -18.14 -136.2 8.9 4 101.9 30.8 7.0 3.84 0.87 0.5468 -18.11 -135.3 9.6 4 101.3 32.1 6.7 4.10 0.91 1.13 PG2122,waterdepthprofileofthelagoon 0 -19.21 -145.3 8.4 0.5 108.4 67.8 7.0 9.01 2.71 1.612 -19.00 -144.0 8.0 0.5 115.0 66.0 7.0 8.52 2.56 1.595 -18.88 -143.6 7.4 2.5 103.7 61.0 7.0 7.99 2.39 1.4810 -18.80 -143.7 6.7 2.8 106.7 60.3 6.9 7.73 2.36 1.4018 -18.85 -143.9 6.9 3.0 88.6 67.4 6.7 8.48 2.48 1.54 PG2131,waterdepthprofileofBaniaLake 0 -16.22 -131.8 -2.0 0.5 92.5 42.6 6.5 5.44 2.05 1.103 -15.92 -130.0 -2.6 2.5 92.1 38.7 6.4 4.69 1.48 0.716 -16.01 -130.9 -2.9 4.0 92.9 40.0 6.5 4.82 1.57 0.78 SurfaceSamples,PG-numberindicatessamplelocation PG2116-X13 -18.48 -138.5 9.3 na 99.4 42.9 6.9 5.52 1.23 1.07PG2116-X14 -18.59 -138.6 10.1 na 96.2 42.5 6.8 5.26 1.20 0.83PG2124 -18.63 -139.4 9.7 na 110.4 37.9 7.0 4.68 1.07 0.77PG2125 -18.43 -138.2 9.2 na 108.9 39.1 7.2 4.91 1.13 0.79PG2126 -18.71 -139.3 10.4 na 113.1 36.6 7.1 4.70 1.10 0.76PG2204 -18.68 -140.0 9.5 na 104.8 38.5 6.9 5.03 1.16 0.79PG2207 -18.72 -140.2 9.6 na 100.9 38.4 6.9 5.00 1.16 0.74

iii

Table5:HydrochemistrydataforallwatersamplestakeninMarch2013continuationofTable4.

Sampledepth K+ HCO3- SO4

2- Cl- Si NO3- Al Sr Fe Mn

[m] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [µg/l] [µg/l] [µg/l] [µg/l]PG2208,waterdepthprofilefofLakeBol'shoeToko 0 0.36 13.58 2.47 0.51 1.93 0.82 79.88 25.86 26.90 <202 0.34 13.12 2.51 0.50 1.91 0.82 77.06 24.85 29.06 <205 0.29 12.81 2.17 0.49 1.74 0.67 69.52 22.44 24.34 <2010 0.27 11.90 2.10 0.49 1.63 0.62 62.67 20.69 <20 <2020 0.28 12.36 2.05 0.49 1.64 0.66 64.51 20.74 20.89 <2030 0.28 11.44 1.99 0.50 1.60 0.72 64.63 20.54 25.16 <2040 0.28 12.36 2.06 0.50 1.64 0.64 66.36 20.87 26.56 <2050 0.28 11.44 2.03 0.49 1.62 0.67 61.63 20.26 <20 <2060 0.27 14.03 1.96 0.49 1.69 0.70 59.92 21.18 24.01 <2068 0.53 14.19 2.01 0.49 1.85 0.69 75.55 22.68 282.36 416.97 PG2122,waterdepthprofileofthelagoon 0 0.40 37.52 0.51 0.55 3.01 0.29 43.19 90.57 147.56 <202 0.40 35.85 0.48 0.53 2.92 0.25 39.73 86.24 142.65 <205 0.38 33.10 0.52 0.51 2.71 0.28 41.63 80.10 132.91 <2010 0.34 32.64 0.48 0.69 2.63 0.33 36.30 78.01 131.20 <2018 0.36 36.46 0.53 0.52 3.10 0.40 29.50 86.03 361.36 375.28 PG2131,waterdepthprofileofBaniaLake 0 0.40 21.81 0.55 0.67 1.27 0.70 42.05 35.17 180.94 <203 0.27 17.69 0.32 0.59 1.21 0.89 37.45 27.86 308.01 77.266 0.32 18.61 0.29 0.53 1.41 0.94 35.95 29.64 451.89 84.19 SurfaceSamples,PG-numberindicatessamplelocation PG2116-X13 0.58 16.78 2.96 0.71 2.30 0.83 73.16 28.59 132.97 20.05PG2116-X14 0.41 16.47 2.91 0.67 2.27 0.85 71.75 27.57 124.64 <20PG2124 0.36 14.80 2.66 0.60 1.98 0.82 75.54 26.28 24.96 <20PG2125 0.40 15.41 2.95 0.60 2.05 0.88 73.31 26.29 33.13 <20PG2126 0.37 15.10 2.77 0.58 2.05 0.89 77.62 26.07 22.22 <20PG2204 0.39 15.56 2.71 0.54 2.13 0.74 84.78 27.42 24.22 <20PG2207 0.37 15.71 2.72 0.51 2.11 0.82 82.18 27.40 24.56 <20

iv

Table 6: Isotope data for water samples taken in August 2012 (sampled by Pestryakova,

measuredatAWILaboratory)

Sampledepth δ18Ο[‰]vs. δD[‰]vs. d-excess[‰]vs. Temperature

[m] VSMOW VSMOW VSMOW [°C]

waterdepthprofiletakeninAugust2012 0 -17.89 -134.4 8.7 11.5

2 -17.97 -135.9 7.9 11.5

4 -17.90 -136.1 7.2 11.5

6 -17.85 -134.2 8.6 11.5

8 -18.04 -134.4 9.9 10.9

10 -18.14 -134.3 10.8 10.2

12 -18.11 -136.9 8.0 9.4

14 -18.36 -140.1 6.8 6.9

16 -18.21 -138.4 7.2 8.7

18 -18.58 -139.3 9.3 6.6

20 -18.41 -139.0 8.3 7.5

22 -18.02 -135.5 8.6 10.3

24 -18.50 -139.5 8.5 7.6

26 -17.98 -136.0 7.8 10.4

28 -18.33 -138.9 7.8 7.5

30 -18.45 -140.0 7.6 6.7

32 -18.61 -141.2 7.7 5.0

34 -18.83 -140.8 9.8 4.8

37 -18.10 -136.8 7.9 6.6

v

AcknowledgmentsIwould like to thankDr.HannoMeyer forhisdedication, effort andpatienceand for the

opportunitytoworkonthisthesisatAlfred-Wegener-Institute,Potsdam.Ialsoliketothank

apl.Prof.Dr.BernhardDiekmann,andDr.BorisBiskabornfortheopportunitytoparticipate

inthefieldcampaigntoLakeBol’shoeTokoin2013andfortheirsupportandcriticalfeedback

regardingthisthesis.SpecialthankstoDr.BernhardChapliginforhiscontributiononsampling

strategy and field preparation. I like to thank Antje Eulenberg for the explanation and

supervision of hydrochemistry analyses. Furthermore, I like to thank all colleagues of the

Yakutia/LakeBol’shoeToko2013Expeditionfortheirhelponwatersamplingandpreparation.

I’mgratefulforthesupportofmyfamilyandChristophMantheygivenatanytime.

IgratefullyacknowledgetheNOAAAirResourcesLaboratory(ARL)fortheprovisionofthe

HYSPLIT transport and dispersionmodel and READYwebsite (http://www.ready.noaa.gov)

usedinthisthesis.

vi

Selbstständigkeitserklärung

Hiermit versichere ich, dass ich diese Bachelorarbeit selbstständig und nur mit denangegebenenQuellenundHilfsmittelnangefertigthabe.AlleStellenderArbeit,die ichausdiesenQuellenundHilfsmittelndemWortlautoderdemSinnenachentnommenhabe,sindkenntlich gemacht und im Literaturverzeichnis aufgeführt. Weiterhin versichere ich, dassweder ich noch andere diese Arbeit weder in der vorliegenden noch in einer mehr oderwenigerabgewandeltenFormalsLeistungsnachweiseineineranderenVeranstaltungbereitsverwendethabenodernochverwendenwerden.Die„RichtliniezurSicherungguterwissenschaftlicherPraxisfürStudierendeanderUniversitätPotsdam(Plagiatsrichtlinie)-Vom20.Oktober2010“,imInternetunterhttp://uni-potsdam.de/ambek/ambek2011/1/Seite7.pdf,istmirbekannt.___________________ _________________________

Ort,Datum Unterschrift