LATE-GLACIAL AND HOLOCENE CLIMATE IN CENTRAL ASIA: LAKE ISSYK-KUL, KYRGYZSTAN

Fluctuations in Central Asian paleoclimate during the last 13,500 years have been investigated by sedimentary and geochemical analyses of deep-basin sediments recovered in a suite of piston and multi-cores collected from Lake Issyk-Kul, Kyrgyzstan. Issyk-Kul is a closed-basin, slightly brackish and oligotrophic lake set in the Tien Shan Mountains in Central Asia. It is the eleventh largest lake in the world by volume (1730km³) and the fifth deepest (668m). Issyk-Kul contains a rich variety of carbonate deep-basin sediments and nearshore calcareous microbialites, as well as a long geologic history of large-scale (10's-100's meters) lake-level change. The lake occupies a critical site under the influence of the prevailing Westerlies, and between the winter Siberian High Pressure Cell and the summer Asian Low. Even subtle changes in moisture and/or temperature due to climatic shifts in the position or intensity of these major atmospheric elements should be strongly recorded in the lake sediments.

Chronologies were established for the cores using radiocarbon and ²¹⁰Pb methods. Additional analyses on selected cores included magnetic susceptibility, grain size, sand-fraction constituents, %carbonate, %TOC, carbonate mineralogy, stable isotope and trace element content of ostracode shells, stable isotopic composition of fine grained carbonates, TEX₈₆ analyses, as well as variations in pollen. Various proxies, such as magnetic susceptibility, stable isotopic content of ostracodes and fine-grained carbonates, and crenarchaeota membrane lipids (TEX₈₆), indicate that prior to 10,500 calyrsBP there was relatively high fluvioglacial input into a smaller and possibly warmer Issyk-Kul. Higher lake levels occurred during the Late Holocene. Evidence exists (particularly in shallower cores) for a subsequent Mid-Holocene regressive event (around 7,400-5,500 calyrsBP) with likely basin closure at that time. Conditions in the basin have remained relatively constant since closure, although fluctuations in various sedimentological and geochemical parameters indicate not only that transient open-basin conditions have existed during the last 5,500 years, but also that the impact of the so-called Little Ice Age and Medieval Warm Period can be seen in the Issyk-Kul record.