Late Quaternary Qaidam lake histories and implications for an MIS 3 ‘‘Greatest Lakes’’ period in northwest China

Da Qaidam and Xiao Qaidam are two of a number of lakes in northwestern China whose lake histories have been used to support the notion of a ‘‘Greatest Lakes’’ period in the region during marine isotope stage (MIS) 3. Reappraisal of the basins’ geomorphology, however, suggests that both lakes are highly problematic proxies for past climate. Xiao Qaidam has a low overflow threshold, only*10–12 m above the lake surface, well below previously estimated high stands, and until about 17–23 ka BP Da Qaidam was occasionally fed by a river whose flow into the lake basin was geomorphically, rather than climatically controlled. Based on limited optically stimulated luminescence dating of shoreline and alluvial sediments it appears that highstands in the basins occurred *100 ka BP or earlier. The two lakes are thus part of an increasing number of lake records that suggest, at least in northwestern China, (1) some lake histories may not record climate events, and (2) that the ‘‘Greatest Lakes’’ high stands occurred much earlier than previously recognized.