Distributions of fatty acids in a stalagmite related to paleoclimate change at Qingjiang in Hubei, southern China

FattyacidsextractedfromasubtropicalstalagmiteatQingjianginSouthernChina'sHubeiProvincewereanalysedusinggaschromatography-massspectrometry.Thesen-alkanoicacidsrangefromC14toC26incarbonnumber,maximizingatC16,withaseconddominanceatC22.Incontrasttothestalagmiteanalysed,theoverlyingsoilsarecharacterizedbythedominanceofheavy-molecular-weighthomologues(＞C20).Then-fattyacidsinthestalagmitewereproposedtobecontributedbyboththesoilecosystemsandthemicrobesharboringinthepercolatingwaterandthecave.Theratiosofunsaturatedtosaturatedn-fattyacids(C16:1/C16:0,C18:1/C18:0)appeartoshowtrendsparablewiththeoxygenisotoperecordsofthestalagmitecarbonate,withenhancedvaluesassociatedwiththecoldepisodesuchasHeinrichevent1.Thispaleoclimate-dependentrecordofthen-fattyacidsmightreflectmicrobialchangesinphysiologyandactivityinresponsetothetemperature.Thisrecordshowssomewhatdifferencefromthepreviouspaleoclimatesignalextractedfromn-alkanolsandn-alkan-2-onesofthesamestalagmite.Theacidrecordfailstodocumentthewell-knownYoungerDryaseventwhichwaseffectivelyshownbythelattertwobiomarkersderivedfromsoilecosystems.Thisdiscrepancymightresultfromthechangingbiogeochemicalimpactondifferentlipidfractionsaswellasthevariedorganismpopulationsindifferentecosystems.

WANGHongmei(SchoolofEnvironmentalStudies,ChinaUniversityofGeosciences,Wuhan430074,China)

CAIYanjun(SKLLQG,InstituteofEarthEnvironment,ChineseAcademyofSciences,Xi'an710075,China)

CHENGHai(DepartmentofGeologyandGeophysics,UniversityofMinnesota,MN55455,USA) 

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