Influence of the Westerlies in arid Central Asia during the Holocene recorded in sediments from lakes Son Kol and Chatyr Kol, Kyrgyzstan

Knowledge about past Asian climate variability and particularly teleconnections between the Westerlies in arid Central Asia and the Monsoon on the Tibetan Plateau is still limited. To reconstruct the Westerlies intensity during the Holocene in arid Central Asia and its effect on vegetation dynamics, we compared the sediment records from alpine lakes Son Kol (273 km²; 13 m depth) and Chatyr Kol (170 km²; 20 m depth), located in the central Tien Shan mountain range (Kyrgyzstan). Both sites differ in the mean annual amount of precipitation received (Son Kol: 550 mm; Chatyr Kol: 260 mm), but show identical recent catchment vegetation (montane grassland). To find out, whether the precipitation primarily causes differences in sedimentary organic matter accumulation, we investigated the distribution of n-alkanes in recent surface sediments from both lakes. The distribution of these biomarkers in Lake Son Kol is dominated by higher input of terrestrial plant material, whereas the one of Lake Chatyr Kol is characterized by mixed input of terrestrial and aquatic material. Additionally, we investigated the n-alkane distributions and compound-specific δD values of radiocarbon-dated sediment cores from Son Kol (core length: 154 cm), dating back to 6000 years BP, and from Chatyr Kol (core length: 625 cm), which dates back to the early Holocene. The combination of terrestrial and aquatic alkane-specific δD values can be used to determine changes of relative humidity. A generally stable n-alkane composition and relatively high amounts of terrestrial biomarkers within the sediments of Lake Son Kol display relatively stable climatic conditions for organic matter production during the mid-to late Holocene. Throughout the record, depleted δD values (-180 ‰) of terrestrial n-alkanes prevail, only periodically interrupted by phases with enriched values (-140 ‰). This suggests a predominance of generally wet conditions due to the influence of the Westerlies with only short-term intercalated dry phases. During the late Holocene, a general trend towards higher n-alkane amounts and more depleted δD n-C29 values is recognized. We conclude that the regional climate was mainly influenced by westerly air-masses, but intensity fluctuations had only minor effects on organic matter accumulation within both lakes. The general trend towards wetter conditions since the mid-Holocene suggests a strengthened influence of Westerlies, bringing more moisture into this region, which is in contrast to monsoonal Asia where a trend towards dryer climate conditions since the mid-Holocene is recognized. It seems that teleconnections between arid Central Asia and the Tibetan Plateau are characterized by anti-cyclic changes in the intensities of the Westerlies and the Monsoon. Keywords: n-alkanes, hydrogen isotopes, sediment, Central Asia, Westerlies, Son Kol, Chatyr Kol