欧亚大陆中北部末次盛冰期以来的湖泊水位变化及其古气候指示意义

湖泊水位高低通常能有效地指示湖盆内湿润条件的变化,进而反映区域有效降水（降水—蒸发）变化,成为重建第四纪古气候演变的重要指标之一。通过对苏联和蒙古国古湖泊数据库以及中国晚第四纪古湖泊数据库中149个湖泊水位变化资料的梳理总结,探讨了末次盛冰期（18 cal. ka BP）以来该地区干湿变化规律及区域分异。根据研究区气候特征、地理位置及已有研究成果将其分为东欧湖泊区、中东亚干旱区和中国北方季风区三大湖区。根据不同水位记录在整个湖泊历史中出现的频率,采用3级重新分类区分出高、中、低3级水量,并把每个湖泊数字化的3级古水量表示成与现代的差值,得到每个湖泊样点每千年时间间隔内相对现代的5级水量变化（很湿润、湿润、无变化、干旱和很干旱）。结果表明,三大湖区末次盛冰期以来可能经历了不同的干湿变化过程：东欧地区湖泊水量记录在晚冰期之前较少,至全新世逐渐增多,且基本表现为早全新世干旱、中晚全新世相对湿润的状况。中东亚干旱区整体呈现出末次盛冰期至中全新世均较湿润而晚全新世干旱的气候状况,但区域内部不同湖泊在起讫时间和强度上存在显著差异。中国北方季风区的湿润期主要发生在早中全新世,但是不同湖泊有所不同。对比分析显示,早全新世时东欧地区东部气候随着斯堪的那维亚冰流的逐渐消退而逐渐变湿润,中全新世由于夏季北欧反气旋东翼的气旋气流增强而达到最湿润状态,西部地区早全新世由于强劲的西伯利亚热高压存在而整体偏干旱,中全新世由于夏季亚洲季风的渗透而转为湿润。中东亚干旱区冰期内的湿润条件可能主要与西风带降水及低温低蒸发有关,而全新世则可能主要与夏季风深入内陆导致降水增加有关。中国北方季风区全新世湿度变化可能主要受东亚季风控制。

Lake level changes of central-northern Eurasia and their indicative significance for paleoclimate since Last Glacial Maximum

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.