Water depth related ostracod distribution in Lake Pumoyum Co,southern Tibetan Plateau

摘要

A modern training set covering 55 surface sediment samples from Pumoyum Co, a freshwater lake on the southern Tibetan Plateau, was analysed in order to quantify relationships between ostracod species distribution and environmental conditions. The extensive data set referring to nine ostracod species includes physico-chemical parameters for water depths ranging between 1 m and 62 m. Canonical correspondence analysis suggests that water depth significantly controls the spatial distribution of modern ostracods in the lake. On this basis, an ostracod-based water depth transfer function was established for reconstructing palaeo-lake levels. The transfer function presents a good correlation between measured and estimated water depth (R~2= 0.87), with a root mean square error of prediction of 15.5 m. This transfer function was applied to fossil ostracod associations of 38 sediment samples from a gravity core which covers the last 6 ka BP. Three stages of lake level fluctuations since 6 ka BP were inferred: a low lake level (～-25 m compared to the present 65 m depth) between 6.0 ka BP and 4.3 ka BP, a fluctuating lake level (-25 to -5 m) from 4.3 to 2.0 ka BP, and a rise from a low level (-25 m) to that of present day within the last two millennia. Together with other proxies including ostracod diversity and grain size as well as total organic carbon and total inorganic carbon content of the gravity core sediments, the water depth transfer function was used to reconstruct past climate change in the Pumoyum Co area as a response to Indian Monsoon dynamics.