Paleoclimatic Change Since The Last Deglaciation Based On N-alkanes And Their Compound Carbon Isotopes In The Sediment Of Lake Xijianhaizi,Inner Mongolia

Paleoclimatic change since the last deglaciation is one of important periods for paleoclimatic research because the climatic history experienced not only a huge transition from glacial to interglacial,but also several abrupt changes,such as,the B?lling-Aller?d,the Younger Dryas(YD)and centennial to millennial-scale variations during the Holocene.In the monsoonal Asia,paleoclimatic changes are complicated by two interacted subsystems(tropical summer monsoon and subtropical summer monsoon system),huge topographical and seasonal difference.There are significant discrepancies both in spatial and temporal scales,and evidenced by instrumental data and paleoclimatic records.Thus,more regional paleoclimatic records derived from different proxies and archives are needed to understand the long-term spatiotemporal pattern of paleoclimate and underlying mechanism.The northern limit of the East Asian summer monsoon(EASM)is located in the transition zone between arid–semiarid and humid area.The lakes in the region are sensitive to climate and environmental changes.In this study,we focus on the Lake Xijianhaizi in Daqingshan Mountains of Inner Mongolia.The sediment chronology is based on the AMS¹⁴C data.Paleoclimatic changes since the last deglaciation(16.4 kyr BP)are reconstructed based on n-alkanes and their compound carbon isotopes.The main conclusions are as follows:1.There are many small,closed lakes in the ridge area of Huitengliang Mountain.These lakes are likely kettle lakes formed by glacial erosion and the melting of a detached mass of glacial ice.Based on the AMS¹⁴C age from lacustrine sediment in the bottom and basement basalt rock,we estimate the Lake Xijianhaizi was formed in last deglaciation(16.4 kyr BP).2.The chronology in the sediment sequence of Lake Xijianhaizi is based on 14 AMS¹⁴C data from plant residues and bulk sediments.3.In this cold region,where the vegetation is dominated by C3 plants,the long-chain n-alkanes(n C₂₉-n C₃₃)are predominantly derived from leaf wax lipids.The compound-specific carbon isotopic values(?¹³C₃₁)are sensitive to regional effective moisture.4.The concentration of short chain n-alkanes in this lake may be an index of lake level or effective precipitation.Aquatic algae and plant were probably less relative abundant and result a low concentration of short chain n-alkanes in the sediment when the lake level was low.The index of concentration of short chain n-alkanes and compound-specific carbon isotope of long-chain normal alkane are agreement,and may be indicator of region effective precipitation.5.According to the change of long-chain n-alkane compound-specific carbon isotopes,during the period of B?lling-Aller?d(14.5–12.9 kyr BP)and the early Younger Dryas(12.9–12.0 kyr BP),the long-chain n-alkane compound-specific carbon isotopes were negative and imply that the effective precipitation were relatively high.In the late Younger Dryas(12.0–11.5 kyr BP)and early Holocene(9.5–8.0 kyr BP),the long-chain n-alkane compound-specific carbon isotope was positive and the effective precipitation might be relatively low.Since the early Holocene,a decreasing trend of?¹³C₃₁ in Lake Xijianhaizi implies increasing effective moisture.This Holocene increasing trend of effective moisture may support previous suggestion that changes of latitudinal temperature gradient would cause an increase in net precipitation in mid-latitude...