中国西北干旱区小冰期的湿度变化特征

Humidity Variability in the Arid Northwest China during LIA Derived from Different Proxy Records

选取中国西北干旱区11条具有明确古湿度指示意义的气候记录,结合冰芯、地层沉积、湖泊沉积、树木年轮、河流阶地等各种研究资料和历史记载,研究中国西北干旱区小冰期的湿度变化。结果表明研究区小冰期(1400-1920AD)从整体而言处于相对湿润的阶段:区内高大山系降水处于较高时段——西昆仑山古里雅冰芯积累量增大,天山山间湖泊水位回升,祁连山敦德冰芯孢粉总浓度增加;而盆地内流系统水量也出现了相应的变化——塔里木盆地克里雅河和塔里木河流量增大,准噶尔盆地艾比湖水位上升,巴丹吉林沙漠地下水补给量上升,居延海入湖水量增大,湖面扩展,青海湖盆地降水增加,有效湿度增大,苏干湖水体盐度降低,入湖水量/蒸发量之比升高。同时,较高分辨率的湿度资料显示,研究区东—南边缘地带在小冰期内部存在次一级的干湿波动,两个湿度较高的时期出现在16世纪和18世纪,分别与小冰期内部的两个相对温暖时期有很好的对应。中国西北相对湿润的小冰期主要是西风带强度增加和位置南移造成该区域降水增多和全球性普遍降温导致有效湿度增大两个因素共同作用的结果,研究区边缘地带小冰期内部冷干暖湿的配置则主要体现了夏季风的影响。

Eleven major humidity proxy records and other supplementary evidences including different natural archives, such as ice-cores, sedimentary records, river terraces, lake-level fluctuations as well as historical documents are involved to reconstruct the humidity variability in the arid Northwest China during the Little Ice Age （LIA） from 1400 AD to 1920 AD. The result shows that as a whole, the LIA is a relatively humid period in this region, contrasting to last 100 years during global warming and medieval warming period. For instance, precipitation in high marginal mountains of the study area was of a high value reflected by the various proxy records from west Kunlun, Tianshan and Qilian mountains. Accordingly, the discharge of big endorheic rivers such as the Tarim and Keliya rivers increased; the surface areas of terminal lakes in desert field expanded, e.g., at Juyan Lake and Ebinur Lake; the water levels rose at lakes in intermontane basins, such as Bosten Lake, Balikun Lake and Qinghai Lake; the groundwater recharge rates in the Badain Jaran Desert were increased; and the water salinity of Sugan Lake also significantly decreased during the LIA. Furthermore, the humidity records with a relatively high resolution from the eastern-southern fringe of the arid Northwest China indicate that there is a secondary oscillation of wet and dry within the LIA. The relatively high humidity during the LIA in Northeast China possibly results from the increase of precipitation in this region due to the strengthening and southward shift of westerlies and the decrease of evapotranspiration caused by the cooling during that time.