藏南错戳龙高湖面阶地的形成时间及相应的古降水量的计算

利用原地生成宇宙成因核素确定了藏南错戳龙的高湖面阶地的形成时间为3.4～3.6kaB.P.。在3.4～3.6kaB.P.之前,错戳龙是外泄的;在3.4～3.6kaB.P.期间,错戳龙的湖水维持在较高水平,降水和蒸发在高湖面保持着平衡;之后随着气温下降,季风减弱,湖泊不断退缩,至今湖面已下降了120m。利用J.E.Kutzbach水能联合方程,对错戳龙高湖面时的降水量进行了计算,结果显示错戳龙在3.4～3.6kaB.P.时年降水量约为530±10mm,之后随着印度季风强度的大幅降低,错戳龙的年降水量至今为320mm,下降了200mm/a。这一结果表明随着全球升温,印度季风将会明显增强,印度季风影响区域的降水也将会显著增加。

EXPOSURE AGES OF HIGH LACUSTRINE SHORELINES AROUND THE CUOCHUOLONG LAKE IN SOUTH TIBET AND RELATED PALEOPRECIPITATION CALCULATIONS

Cuochuolong is a small closed lake located in Jilong County in South Tibet,with its drainage and lake area of 540km2 and 17km2,respectively.It is at an elevation about 4600m,about 20km away from the Yarlung～Tsangpo River.Under the Indian Monsoon influence,it currently receives annual precipitation of about 320mm.Using in situ produced cosmogenic nuclides ¹⁰Be and 26Al we have dated high lacustrine shorelines around the Cuochuolong Lake: The exposure ages are 3.4ka for a bedrock terrace at 4723m and 3.6ka at 4710m.From the results we can infer that the Cuochuolong Lake drained before 3.4～3.6kaB.P.It was kept at a high water level during 3.4～3.6kaB.P.After that the lake has been shrunken vertically over ca.120m along with the cooling which weakened the strength of the Indian Monsoon in South Tibet.The changes of water levels are the joint result of precipitation,melting glaciers,balance of outflow and evaporation,all of which are related to paleo-environmental changes on the Tibetan Plateau.Based on J.E.Kutzbach's hydrologic and energy balance model,we calculated the annual precipitation in Cuochuolong at 3.4～3.6kaB.P.to be 530±10mm/a,which is ca.200mm/a higher than at present.Our results show that in response to global warming precipitation will increase significantly in the Indian Monsoon regime,which is much higher than the average result of the world.