Bachelor Thesis Variability of the Isotopic and ... · of Lake Bol'shoe Toko, SE Yakutia, Russia...
Transcript of Bachelor Thesis Variability of the Isotopic and ... · of Lake Bol'shoe Toko, SE Yakutia, Russia...
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.
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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
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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.
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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.
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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