Liu, Shirley Xiaochun2020-04-212020-04-211999-08https://hdl.handle.net/11299/212494A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Shirley Xiaochun Liu in partial fulfillment of the requirements for the degree of Master of Science, August 1999.The environment of Lake Issyk-Kul, Kyrgyzstan, has experienced significant changes since the early Holocene due to climate change. Two piston cores, IK97-10P and IK97-11P, were analyzed for ostracode abundance. These data were interpreted in light of the isotopic and trace element composition of the ostracode shells generated in a companion study to aid in the paleoenvironmental reconstruction of Lake Issyk-Kul. In this study, 23 species of five genera of ostracodes have been identified in the lake sediments. Most of them are endemic to the lake. Five units were recognized ranging in age from 7900 to 1000 years (ka) based on both geochemistry and the ostracode assemblage record. Water salinity, primary productivity and oxygen content in the bottom water may all affect the distribution of ostracode species. Salinity level is reflected by the ?18O composition and the Sr/Ca ratio of the ostracode shells. The abundance of total organic carbon (TOC) in the sediment is interpreted as a measure of primary productivity, and is closely related to the level of food supply to the benthic enviroment where ostracodes live. Dissolved oxygen in the bottom water is indicated by the U/Ca ratio in the ostracode shells. The geochemical record suggests an early Holocene humid episode dated by 14C at 7.9 ka-6.1 ka. This episode was followed by a transitional period from wet to dry conditions around 6100 BP. Since then Lake Issyk-Kul has experienced relatively dry conditions. The geochemistry data and ostracode assemblage changes correlate quite well. Corresponding responses can be detected in ostracode assemblages at the species level, but not at the genus level. The climatic pattern of central Asia appears to show both global and regional features. In general, a wet early Holocene followed by a dry late Holocene and a transition between the wet phase and the dry phase are common to most of Central Asia. However, due to the topographic complexity in the region, some areas show a strongly regional character.enPlan As (thesis-based master's degrees)Department of Earth and Environmental SciencesUniversity of Minnesota DuluthMaster of ScienceMaster of Science in GeologyThesis or Dissertation