Holocene Climate Change Recorded By Lake Balikun, Eastern Xinjiang

It is valuable to understand the global climate system and man-land relationship by studying the Holocene climate change. The moisture evolution in arid inland is concerned of hydrological recycling, ecological system and development of the social economy. It also controls the nutrient transportation to the ocean and plays a key role to influence the ocean primary productivity. Comparing to its vast area, the distribution of the high-resolution paleoclimate records in arid Central Aisa is non-uniform. These conditions hinder the understanding of the spatial and temporal evolution of the regional effective moisture.Lake Balikun in eastern Xinjiang is the material for this research. A 863cm core (BLK.06) was obtained in the southern part of the lake, and our research focused on the Holocene period (the upper 400cm). It was sampled by 1cm interval in the lab, and age model was defined by radiocarbon dating. Carbonate content, grain size, magnetic susceptibility, loss-on-ignite and carbonate stable isotope was analyzed to reconstruct hydrology and climate evolution since 8.6 cal. ka B.P. We draw the following conclusions:1. Holocene lake water oxygen isotope change in Lake Balikun1) Melt water is the primary source of the Lake Balikun. The stable isotope value of the input water is similar to the annual weighted-average oxygen isotope of the precipitation.2) Carbonate oxygen isotope of BLK06 reflects the oxygen isotope of the lake water. The influence of the detrital carbonate, disequilibrium fraction and the temperature to the fine-grain carbonate oxygen isotope of BLK06 was eliminated by proxies like grain size, magnetic susceptibility, carbonate deposition rate and mineral type.3) Carbonate oxygen isotope recorded by BLK.06 is comparable to the other record in the same lake published earlier. The difference between the cores attributes to the different age model and location of the core.2. Holocene lake evolution pattern of Lake BalikunMulti-proxy analysis shows Lake Balikun experienced the following stages during the Holocene:before 8.6 ka, the lake was very small, and there was no lacustrine sediment in the site; 8.6-7.9 ka, Lake Balikun gradually expanded and carbonate sedimentation environment initialized; 7.9-6.1 ka, the input of magnetic mineral led by the glacial activity changed significantly, while the river inflow was stable; 6.1-4.2 ka, the environment of Balikun was dominated by low temperature, and interpretation of the lake level proxy was disturbed by the dramatic change of the temperature; 3.3-0 ka, the lake level fell down gradually, and the modern hydrologic environment of Lake Balikun was formed since 2.2 ka.3. Comparison of the lacustrine oxygen isotope records in arid Central Asia1) Lacustrine records with reliable age control and high-resolution are selected to do empirical orthogonal function analysis (EOF). The result shows that the gradually positive trend during 8.1-1.0 ka was the major tendency of the lacustrine oxygen isotope records in arid Central Asia. This tendency is beneficial from the change of precipitation oxygen isotope from different water source in arid Central Asia (polar airmass, westerly system and Asian monsoon system) and the change of local winter precipitation, while the contribution of the effective moisture is not significant.2) The role of summer precipitation contributing to the weighted annual mean oxygen isotope changes from place to place in arid Central Asia. It leads to the discrepancy of vegetation and lacustrine oxygen isotope as local effective moisture proxy.4. Middle to late Holocene effective moisture change in arid Central Asia.1) Spatial and temporal moisture evolution pattern of moisture change reconstructed by lacustrine pollen records in arid Central Asia was analyzed by EOF method. Moisture in the study area is jointly controlled by solar insolation tendency and the climatic response of the different vegetation.2) Humidity change associated with Mongolia High and Asian winter monsoon has only occurred at the north rim of the arid Central Asia, but not all of the study area.3) The signal of north Atlantic oscillation (NAO) covered by pollen records in arid Central Asia is decoded by the EOF analysis. Unfortunately, the NAO signal is very weak comparing to the others, which suggested that the influence of NAO to the climate change in arid Central Asia is not significant.