Lake-level records support a mid-Holocene maximum precipitation in northern China

摘要

Lake level and its inferred East Asian summer monsoon(EASM)evolution in northern boundary of EASM during the Holocene are highly debated.Here,we present a 15-ka record of glycerol dialkyl glycerol tetraethers(GDGTs)in a closed lake in northern China to address this issue.Surface and downcore sediment data demonstrate sedimentary GDGT-0 and branched GDGTs(brGDGTs)are of aquatic production.Contents of GDGT-0 and brGDGTs increase but brGDGT-based paleo-temperature proxy decreases with water depth in surface sediments along a nearshore to offshore transect.This trend is likely due to an increasingly hypoxic condition,favored by anaerobic microbes producing these GDGT-0 and brGDGTs,in bottom water.Accordingly,brGDGT-derived water temperature and pH would reflect bottom water conditions that are largely regulated by water depth of the lake.Downcore GDGT data and their derived temperature and pH consistently reveal a gradually increasing lake level from the late Pleistocene to the early Holocene,a high level during 9.5-5 ka BP and a decreasing trend afterward.The lake-level records from independent and robust proxies in this study largely agree with pollen records in the region,supporting a mid-Holocene maximum EASM precipitation.