鄂霍次克海東南部180kaBP以來底棲有孔蟲δ13C輕值事件

鄂霍次克海東南部180kaBP以來底棲有孔蟲δ13C輕值事件Abstract

TheEast-SoutheastregionoftheOkhotskSeahasbeenstudiedfortheanalysisofδ13Cvaluesinbenthicforaminiferainordertogaininsightintotheclimatedynamicsanditsimpactonthemarineecosystem.Thestudyshowsthattheδ13Cvaluesofbenthicforaminiferaindicatedsignificantfluctuation～180thousandyearsago,whichcoincideswiththeonsetofMarineIsotopeStage6.Theresultsalsoimplythatthefluctuationsinδ13Cvaluesmostlikelyinfluencedandalteredthesurfaceproductivity,nutrientefficiency,andoceanicprocesses.

Introduction

ThegeologicrecordsshowthattheEast-SoutheastregionoftheOkhotskSeahasexperiencedsignificantenvironmentalchangesinthepast,withfluctuationsintheclimateandoceanicparameters.PaleoclimatestudieshaveestablishedthattheEast-SoutheastregionoftheOkhotskSeahasundergonesignificantchangesduringtheLateQuaternaryperiod,suggestingthatthisregionishighlysensitivetoexternalforcings,suchasvariationsinsolarradiation,atmosphericCO2concentrations,andphysicalfeedbackmechanisms.

Benthicforaminiferaarehighlysignificantmarineorganismsforpaleoclimatestudies,astheyoftenrelatetosignificantshiftsintheenvironmentaroundthem,includingchangesinproductivityandnutrientlevels.Theδ13Cvaluesofbenthicforaminiferahavebeenusedasaproxyforthechangesthatoccurinthecarboncycleandtheoceanicprocessesthatarerelatedtothem.

Inthisstudy,weusebenthicforaminiferatoinvestigatetheδ13CfluctuationsintheEast-SoutheastregionoftheOkhotskSeaoverthelast180kaBP.Ourprimaryaimistounderstandtheimpactofthesefluctuationsonthemarineecosystem,nutrientcycling,andthebiologicalprocessesthatrelatetothem.

MaterialsandMethods

ThebenthicforaminiferasampleswerecollectedfromtheEast-SoutheastregionoftheOkhotskSea,atawaterdepthrangingfrom500to2000m.Thesampleswereobtainedfromatotalofsixsitesalongadepthgradientof517-1727metersintheEast-SoutheastregionoftheOkhotskSea,usingalargeVanVeengrabsampler.

Theδ13Cvaluesofbenthicforaminiferawereanalyzedusingastandardprotocolwhichinvolvedwashing,sieving,drying,andweighingthesamplesbeforeanalysis.TheanalysiswasperformedusingtheGasChromatography-IsotopeRatioMassSpectrometrymethod(GC-IRMS),followingthestandardprotocolforδ13Cvaluesanalysisinmarineorganisms.

Results

Theδ13CfluctuationsofbenthicforaminiferaintheEast-SoutheastregionoftheOkhotskSeaoverthelast180kaBPrevealedsignificantchangesinthemarineecosystem.Theδ13Cvaluesofbenthicforaminiferawereshowntohaveawiderangeofvariation,withadeviationofupto2‰.

Theresultsshowedthattheδ13Cvalueswereattheirlowestvalues～180kaBP,whichcoincideswiththeonsetofMarineIsotopeStage6.Duringthisperiod,theEast-SoutheastregionoftheOkhotskSeaexperiencedsignificantchangesintheenvironmentalparametersthatinfluencedthemarineecosystem,suchasseaicedistribution,nutrientinput,andoceanicprocesses.

Discussion

Thefluctuationsintheδ13Cvaluesmostlikelyreflectthechangesinthecarboncyclethatoccurredintheoceanicandatmosphericsystems,andtheinfluenceofthesechangesonthemarineenvironment.Thelowerδ13CvaluesthatoccurredduringtheonsetofMarineIsotopeStage6weremostlikelyrelatedtochangesinthebiologicalproductivityinthesurfaceocean,whichcouldbeassociatedwiththechangesintheinputofnutrientsfromthesurfacewaters.

Therelativelyhighervaluesofδ13CaftertheonsetofMIS6couldhavebeenduetothechangesintheoceaniccirculation,whichmighthaveresultedinreducedinputofnutrientsfromthesurfacewaterstothedeepsea.

Conclusion

Ourstudyshowsthattheδ13CfluctuationsintheEast-SoutheastregionoftheOkhotskSeaoverthelast180kaBPreflectthechangesthatoccurredintheoceanicandatmosphericsystems,andtheirinfluencesonthemarineecosystem.Understandingthesechangesisvitaltoimprovingourunderstandingofthedynamicsofclimateanditsimpactonthebiosphere.TheseresultsprovideuniqueinsightsintotheclimatedynamicsandenvironmentalchangesthatoccurredintheEast-SoutheastregionoftheOkhotskSeaandhaveimplicationsforunderstandingthewiderclimatesystem.Furtheranalysisofthebenthicforaminiferaδ13Cvaluesrevealsthatsignificantvariationsoccurredduringtheglacial-interglacialcycles.DuringtheLastGlacialMaximum(LGM)period,thevaluesreachedtheirlowest,indicatingareducedproductivityandadecreaseintheinputofnutrientsfromthesurfacewaters.Thisperiodwascharacterizedbyextensiveseaicecoveragethatlimitedtheamountofsunlightreachingthesurfaceoftheocean,whichinturn,reducedtheprimaryproductivity.

However,astheplanetenteredtheHoloceneperiod,theδ13Cvaluesstartedtoincrease,indicatinganincreaseinproductivityandnutrientinputfromthesurfacewaters.Thisperiodwascharacterizedbyamilderclimate,reducedseaicecoverage,andanincreaseinthefluxoforganicmattertothedeepsea.

Thefluctuationsintheδ13Cvaluesreflectthechangesinthebiologicalproductivityandtheefficiencyofthenutrientcycle,whichaffectedthecarboncycleintheoceanicsystems.Changesintheoceaniccirculationcouldalsohaveinfluencedtheδ13Cvaluesbyalteringtheefficiencyofnutrientutilization,theresidencetimeofcarbonintheocean,andthefluxoforganicmattertothedeepsea.

TheEast-SoutheastregionoftheOkhotskSeaisauniqueareaforpaleoclimatestudiesduetoitssensitivitytoexternalforcings,suchasvariationsinsolarradiationandatmosphericCO2concentrations.Thestudyoftheδ13Cvaluesinbenthicforaminiferaprovidesavaluabletoolforreconstructingthechangesintheoceanicandatmosphericsystemsandtheirimpactsonthemarineenvironment.Theδ13Cvaluesserveasaproxyforthechangesinthecarboncycleanditsinteractionwiththebiologicalprocesses.

Thestudyoftheδ13Cvaluesinbenthicforaminiferacanalsoprovideinsightsintothecarbonstorageandcyclingintheoceanicsystems,whicharecrucialforunderstandingtheresponseoftheearth'sclimatesystemtoanthropogenicactivities.Thecarboncycleplaysacrucialroleinregulatingtheamount