2001-西宁黄土堆积记录的最近13万年高原季风气候(11)

lation,absolutedatingandgeomorphologicobservationstendtosuggestthattheloess2pa2leosoldepositswereformedduringthelastglacialcycle.

Wemeasuredmagneticsusceptibility,frequency2dependentsusceptibility,calciumcar2bonatecontent,whichareregardedasgoodproxyoftheplateausummermonsoon(PSM)strength.Thegrain2sizedistributionisregardedasasensitiveproxyindexoftheplateauwintermonsoon(PWM)strength.Theresultsshowthatthesummermonsoonwasunusual2lystrengthenedduringtheperiodcorrelatingtothemarineisotopestage5e,andstrengthofthePSMin5aand5cwasclosetothestage3.ThePWMwasfrequentlychangedinthestage3indicatedbythegrainsizerecord.ThereareexistedphaselagandleadbetweenthePWMandPSMrecords,thetwosystemswerenotco2variationsduringthelast0.13Ma.

Therearesub2orbitaltimescalevariationsinboththegrain2sizeandfrequency2depend2entsusceptibilityrecords,butwecannotseparatethelocalandregionalclimatesignalsfromtheserecords.Webelievethat,mixtureoflocalandregionalclimaticsignals,timereso2lutionaswellasnon2detaileddatingoftheloess2manyuncertaintiesinthelong2distanceclimaticcorrelationpreviousconclusionthattheclimaticinshouldbefurtherexamined.

Qinghai2XizangPlateauwillspatiallyandtem2porallyrecords.Apreliminaryresultofgrain2sizeandmagneticsusceptibilitymeasurementofa2Macontinuousloess2paleosolsequencehasshownthePWMwashigh2frequencyvariationsinthepast,andthereexistedclearandregular10yeartimescalecyclesinthePWMchanges.TheperiodofthestrengthenedPSMwasshorterthanthatofthePWM.However,theremaybeotherexplanation:therecordispartly“misleading”becauseimplicationoftheproxyindexofpaleoclimatesuchasmagneticsusceptibilityoftheloessinQinghai2XizangPlateauisnotveryeffective.Apreliminarypaleosolinvestigationhasshownhighvariabilityofthesoildepositswithspace,thiscertainlyindicatesthelocalenvir2onmentisacutelyheterogeneousinQinghai2XizangPlateau.Theenvironmentchangesarerelatedtotheupliftprocessoftheplateau.Therefore,investigationsoftheorigin,trendandvariabilityoftheplateaumonsoonclimatemayprovideinformationoftheupliftprocessoftheplateau.Tounderstandthechangingplateaumonsoonwillbefundamentaltopredicttheen2vironmentchangesinandaroundtheQinghai2XizangPlateau,andthisregionissensitiveandvulnerabletoglobalchange.Therearestillsomeuncertaintiesinreconstructingthepaleocli2mateofthelastglacialcyclebytheloessdeposit.Investigationsoftheorigin,implicationsoftheproxyindexesandagesoftheloessdepositswillberequired,andthesewillcertainlyoffermuchmoreinformationabouttheplateaumonsoonchangesduringthelateCenozoicEra.

Keywords　　Qinghai2XizangPlateau,loess,plateaumonsoon,thepast0.13Ma,cli2maticeventcorrelation4