Ostracods and stable isotopes of a late glacial and Holocene lake record from the NE Tibetan Plateau

Abstract

Ostracod assemblage changes and stable isotopes of ostracod shells were used to reconstruct the salinity history of Lake Donggi Cona on the northeastern Tibetan Plateau in response to the late glacial and Holocene climate history. Brackish and relatively unstable conditions were inferred for the earlier part of the late glacial between 18.9 and 13.4 cal ka BP and for the early to mid Holocene (11.9–6.8 cal ka BP). A saline lake existed in the intervening period probably representing colder and drier conditions during the Greenland Stadial 1 (= Younger Dryas in North Atlantic region). Freshwater conditions similar to the present stage of Lake Donggi Cona were established for the first time at 6.8 cal ka BP. This inference and the implied increase in moisture availability in the latter half of the Holocene is in contrast to most climate records from the Tibetan Plateau which suggest drier and colder conditions. However, three lake records from the eastern Tibetan Plateau including our new record show that the Holocene insolation-driven monsoonal weakening and temperature decrease caused a catchment-specific, opposite response of the moisture availability in comparison to those at the majority of sites. Catchments with relatively low precipitation at present experienced apparently a moisture availability increase during the colder second half of the Holocene in contrast to the inferred drier conditions at predominantly generally wetter sites. The increase in moisture availability at relatively dry sites mainly results from the lowered temperature and evaporation but is probably further controlled by a complex of factors including the amount and timing of precipitation, the altitudes of the lake basins and upper reaches, and the existence or development of glaciers, snow fields and frozen ground in a given catchment. Our record from Lake Donggi Cona suggests that the recently observed reduction in Yellow River discharge in response to present global warming will likely continue or even increase under warmer climatic conditions in the future.