欧亚大陆湖泊记录和两万年来大气环流变化

EURASIAN LAKE-LEVEL RECORDS AND CHANGES IN PATTERNS OF ATMOSPHERIC CIRCULATIONS DURING THE LAST 20 000 YEARS

159个湖泊地质记录提供了欧亚大陆两万年来大气环流变化信息。盛冰期北欧低湖面而地中海地区高湖面，反映冰流反气旋控制和西风带南迁。随着晚冰期冰流高压减弱、西风带回迁，南欧为低湖面而北欧低湖面范围减小。全新世早中期北欧阻塞高压发展，干燥炎热；南欧地区性季风环流加强，气旋雨增加。中国青藏高原至东西伯利亚高湖面，反映东亚季风扩张、季风雨以及高原对流雨增加。晚更新世以来湖泊所反映的西风带和季风环流变化，揭示了辐射异常和北半球冰流消长的动力控制。

The use of lake-level data to reconstruct climatic changes is based on an understanding of the relahonship between the local water balance and lake voltime; the idea that regionally-synchronous lake-level changes reflect climate changes, the fact that changes in the broad-scale patterns of regional climates can be interpreted as a direct reflection of changes in atmospheric circulation patterns; and the availability of continental-scale syntheses of lake-level data through the construction of data bases. In thes study, 159 lake records extracted from three lake-status data bases documenting the changes in water balance from northern Eurasian continent has provided climates of precipitation and P-E and showed regionally-coherent patterns of changes in westernes and monsoons during the late Quaternary.The lake data from the Mediterranean region show that the lake levels are high at the Glacial Maximum, low during the Late Glacial period, and then high again during the early to mid-Holocene. The present day is the driest interval during the last 20 000aB. P. This temporal patterns suggests that the lake record from the Mediterranean region reflects the interplay of two major climatic systems: the Westerlies and the monsoon. Wetter conditions during the hot Glacial Maximum likely reflect an increase in depressional rainfall resulting from the southward displacement of the Westerlies consequent on the existence of the large mountain-like mass of the Laurentide ice sheet.Holocene wetter conditions in the northern Mediterranean could represent a local monsoon-like phenomenon, generated by the insolation-induced increase in land-sea contrast, and related to the summer storms characteristic of the Mediterranean Sea at the present day.The lake data from northern Europe show tWo phases of drier than present conditions, during the Late Glacial period, and during the mid-Holocene, but differences in the area affected indicate that different changes in circulation were involved. At the Glacial Maximum, the development of a glacial anticyclone throughout the year resulted in drier conditions along the margin of the Scandinavian ice sheet. This effect likely attenuated during the Late Glacial period. This drier conditions only disappears with the final rapid disintegration of the ice sheet in the early Holocene.The zone of drier conditions during the early to mid-Holocene was centred on the Baltic, and appears to have resulted from the development and persistence of blocking anticyclones in summer. The incidence of blocking anticyclones over Scandinavia and the Baltic increases when the westerly flow is weaker than normal.The lake data from eastern and central Eurasia provide a record of the expansion of the Asian Monsoon during the Holocene. At the beginning of the Holocene, lakes in the Balkal region and Mongolia show conditions drier than present By 6 000aB.P.,lakes in western Siberia, Mongolia and as far north as Yakutia register conditions wetter than present. Thus, the lake data suggest that the expansion of the Asian Monsoon was at a maximum in the mid-Holocene, considerably lagging the driving changes in insolation forcing.The lake data suggest that the interior of northern Eurasia, from the Urals to Yakutia, experienced a more positive water balance at 6 000aB.P. compared to present,associatod with cyclone activity on the downstream limb of the summer anticyclone in the west and monsoon penetration in the east.These analyses of the lake data from northern Eurasia show that for any given region similar climatic responses of a more or a less positive water balance can be caused by markedly different changes in the cireulation regime resulting from fundamentally different global forcing of the glacial or insolation changes. Lake records from northern Eurasia show regionally-coherent patterns of changes during the late Quaternary. Lakes peripheral to the Scandinavian ice sheet were lower than today but lakes in the Mediterranean zone were high at the Glacial Maximum, reflecting the dominance of glacial anticyclonic conditions in n