Ahydrocarbonbiomarkerrecordforthelast40kyrofplant inputtoLakeHeqing,southwesternChina ZhaohuiZhang a, *,MeixunZhao a ,XiangdongYang b ,SuminWang b , XuezhongJiang b ,FrankOldfield c ,GeoffreyEglinton a,d,e a Department of Earth Sciences, 6105 Fairchild Hall, Dartmouth College, Hanover, NH 03755, USA b Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 21008, PR China c Department of Geography, University of Liverpool, Liverpool L69 7ZT, UK d Biogeochemistry Centre, Earth Sciences Department, University of Bristol, Bristol BS8 1RJ, UK e Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA Received2May2003;accepted14December2003 (returnedtoauthorforrevision7September2003) Abstract Multiproxyrecordsrelatingtoclimateandvegetationhavebeenobtainedforacorespanningthelast40kyrfrom the Heqing Lake Basin (26  N, 100  E; 2200 m asl.), Yunnan Province of southwestern China. Compound-specific carbonisotoperecordsforthevascularplantleafwaxhydrocarbons,theC 23 –C 33 n-alkanes,andforthealgalhydro- carbons,theC 23 andC 25 n-alkenesandaC 30 cyclobotryococcatriene,allshowashiftofcirca+3% in d 13 Cvalues fromMIS3totheendofMIS2,followedbyarapidreturntolightervalues.Thisshift(from 32to 29%)forthe n-alkanes and n-alkenes most likely derives from bicarbonate utilization by aquatic plants in the lake, rather than increased C 4 photosynthesis. Thus, both pollen data and hydrocarbon data appear to reveal a rise and fall in the contributionsofsubmergedand/orfloatingplantsduringMIS2. # 2004ElsevierLtd.Allrightsreserved. Keywords: Heqing Lake; Yunnan; China; LGM; Compound specific d 13 C; n-alkanes; n-alkenes; Cyclobotryococcatriene; Magnetic susceptibility;Pollen;Algae;Aquaticplants;C 4 vs.C 3 plants;Paleoenvironment 1. Introduction The present climate of large parts of China is dominated by seasonal changes in wind and precipita- tionknownasmonsoons.SoutheastChinaiscontrolled by the East Asian monsoon while Southwest China is dominated by the southwest (Indian) monsoon. In the summer, the continent warms rapidly relative to the Pacific Ocean and Indian Ocean and higher pressure overtheoceansgiverisetothestrong,low-level,atmos- pheric pressure gradient that in turn generates the southeast and southwest summer monsoons, respec- tively(Fig.1A).Inthewinter,thecontinentcoolsrela- tive to the ocean, the pressure gradient completely reverses, and the dominant flow becomes northeasterly and northwesterly (Fig.1B)(Overpeck et al., 1996).In the summer, the warm and moist oceanic air collides with colder continental air, generating the bulk of the rainfall. Heqing Basin is located in Yunnan Province, southwestern China where the southwestern (Indian) monsoon prevails. Subtropical evergreen forest is the 0146-6380/$-seefrontmatter # 2004ElsevierLtd.Allrightsreserved. doi:10.1016/j.orggeochem.2003.12.003 OrganicGeochemistry35(2004)595–613 www.elsevier.com/locate/orggeochem * Corresponding author at Present address: Department of Earth, Atmospheric, Planetary Sciences, E34-166, Massachu- setts Institute of Technology, 77 Massachusetts Avenue, Cambridge,MA02139,USA.Tel.:+1-617-253-8352;fax:+1- 617-253-8630. E-mail address: zhaohui@mit.edu(Z.Zhang).