Climatic and limnological changes 12,750 to 3600 years ago in the Issyk-Kul catchment, Tien Shan, based on palynology and stable isotopes

Arid Central Asia is at the border between the prevailing Westerlies and monsoonal climates. Lake Issyk-Kul, a large mountain lake, and its sediment record are key to reconstructing complex interactions between these two major climatic systems over time. We present for the first time sedimentological (magnetic susceptibility, CaCO₃, δ¹³C and δ¹⁸O values of benthic ostracods and fine-grain carbonates) and palynological investigations of a sequence covering the last 12,750 years, with additionally some proxies at a lower resolution above 3590 years ago. From 12,750 until 10,000 years ago, vegetation reflects desert to semi-desert conditions around the lake. Soil erosion is intensive as reconstructed from high Glomus percentages and high magnetic susceptibility. The values of fine-grain carbonate δ¹⁸O are very negative. This is explained by intensive glacial meltwater runoff from surrounding mountain tops and slopes. Negative δ¹³C values of carbonates reflect the presence of C3 plants near the glacial edge, such as Kobresia sedges. From 10,000 to c. 6500 years ago, the increase of the Artemisia steppe occurring at the same time as an increasingly positive trend in fine-grained carbonate δ¹⁸O values are apparently contradictory. This is interpreted by a Westerly trend (increasing humidity) at the altitude of the lake (1607 m) and a monsoonal trend (increasingly dry) at the elevation of the glaciated mountain tops (a reconciliation hypothesis developed for multiple sites, illustrated here within one site only). Whereas the steppe is widespread around the lake, the fine-grain carbonates are precipitated from surface waters strongly influenced by meltwater having spilled down the surrounding mountains that are >2 km higher. Additionally after low lake levels until 10,000 years ago, our data suggest a lake level rise between 10,000 and 8000 years ago.