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

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.