Ostracoda assemblages in core Sediments and their environmental significance in a small lake in northwest tibet, China

A 107-cm-long lake core was drilled in South Hongshan Lake (35 degrees 10'N, 80 degrees 04'E, 5060 m a.s.l.) shows 150 yr of environmental change as inferred from ostracoda assemblages. Four species of ostracoda, which belong to four genera, have been identified. The ostracoda distribution in the core can be divided into six ostracoda assemblages as follows: OA1 - Ilyocypris biplicata-Limnocythere inopinata assemblage; OA2 - Limnocythere inopinata-Leucocythere mirabilis assemblage; OA3 - Leucocy there mirabilis-Limnocythere inopinata assemblage, in which dominant species is Limnocythere inopinata; OA4 - Nearly ostracoda free; OA5 - Eucypris inflata-Limnocythere inopinata assemblage; and OA6 - Limnocythere inopinata changes from dominant to sole species. These ostracoda assemblages, together with other proxies, imply the following environmental sequence for the past 150 yr in the study area. Shallow moving water appears in A.D. 1850-1884, followed by a warm-humid climate in 1884-1922. Lake level decreased and water temperature supported maximum ostracoda growth in 19221946, followed by cooling conditions in 1946-1960. From 1960 to 1980, declining lake level is closely linked with local precipitation. The period since 1982 is characterized by less precipitation and continuous aridity under warming climatic conditions