关键词: 末次盛冰期, 湖泊水位变化, 古气候变化, 欧亚大陆中北部

Abstract:

Fluctuations of lake level are good indicators of broad-scale wetness and thus can reflect the changes in the moisture balance (precipitation minus evaporation), which has been an important index in reconstructing the paleoclimate of late Quaternary. Spatial and temporal patterns of humidity changes since Last Glacial Maximum (LGM, 18 cal. ka BP) have been reconstructed for central and northern Eurasia based on the compilation of 149 lake records from the database documentation of the Soviet Union and Mongolia as well as China. The study areas were divided into three regions according to the climate differences, geographic locations and existing research results, that are, the Eastern Europe lake region, the arid Central Asian lake region and the East Asian monsoon lake region of northern China. A three-category scheme (collapsed coding) was used here to reclassify different lake statuses in order to standardize the lake level data over the past 18000 years. Then we used five-scheme status anomaly within each 1000-yr interval and the present to map and analyze the spatial patterns of five levels, namely, much drier, drier, no change, wetter and much wetter than today. The results demonstrated that moisture conditions have experienced diverse changes since LGM in different lake regions. There were relatively few lake records in Eastern Europe before late glacial period and the records increased substantially since the Holocene. Arid climate prevailed during the early Holocene in Eastern Europe, and relatively wet conditions dominated the middle and late Holocene. The arid Central Asian lake region as a whole experienced a wet climate from the LGM to the middle Holocene and turned dry during the late Holocene. But the patterns of climate change differed from lake to lake. In the East Asian monsoon region of northern China, the wet period was mainly observed in the early and middle Holocene and then the climate became drier in the late Holocene. The comparative analysis revealed that the eastern part of Eastern Europe lake region presented a wet trend with the retreat of the Scandinavian ice sheet during the early Holocene and the humidity reached a maximum in the mid-Holocene associated with cyclone activity on the downstream limb of the summer anticyclone. However, the western part of Eastern Europe experienced drier conditions in the early Holocene due to the development of a strong thermal high-pressure cell over central and western Siberia, and then returned to wetter conditions in the mid-Holocene as the result of the penetration of the Asian monsoon. The relatively wet condition in the arid Central Asian lake region during the glacial period was mainly produced by the precipitation brought by the westerlies and the significant decrease in evaporation, while the wet mid-Holocene was probably related to the strengthening of summer monsoon precipitation. The regional climate may have been mainly controlled by East Asian monsoon in the monsoon region of northern China.

Key words: LGM, lake level changes, paleoclimate changes, the central-northern Eurasia