24kaB.P.以来青藏高原中部湖泊演化及古降水量研究——以兹格塘错与错鄂为例

PRELIMINARY STUDY OF LAKE EVOLUTION AND PRECIPITATION OF ZIGETANGCO AND COE BASINS,CENTRAL QINGHAI-XIZANG PLATEAU,SINCE 24kaB.P.

古湖泊砂砾堤研究表明 ,2 4kaB .P .,兹格塘错、错鄂分别存在 1 0m、3 0m(高出现代湖面 )的高湖面 ,湖泊面积分别可达 2 72km2 、2 2 0km2 ,是现代湖泊的 1 .42、3 .1 2倍。与此相比 ,9.0— 6 .0kaB .P .湖面略低 ;在兹格塘错 ,古湖泊高出现代湖面 8m ,面积约为 2 4 6km2 ,比现代大5 6km2 ;在错鄂 ,古湖面高出现代 1 2m ,面积约为 1 3 8km2 。基于Kutzbach水能联合方程 ,利用逐次逼近法取得有关参数 ,重建的各流域上述各时期的降水量分别可达 (40 0± 2 0 )mm/a (兹格塘错 2 4kaB .P .)、(5 3 5± 2 0 )mm/a (错鄂 2 4kaB .P .)、(3 70± 2 0 )mm/a (兹格塘错 9.0— 6 .0kaB .P .)、(470± 2 0 )mm/a (错鄂 9.0— 6 .0kaB .P .)。

Evidence from gravel-sand bars around lakes shows that the lakes in the central Qinghai-Xizang Plateau have at least four high-level stages since 24kaB.P.. 24kaB.P. and 9.0-6.0kaB.P. high lake level stands are discovered in Zige Tangco and Coe catchment basins. 15.5kaB.P. and 2.2kaB.P. high lake levels are discovered in Zige Tangco and Coe basins, respectively. During the periods of around 24kaB.P. and 9.0-6.0kaB.P.,in the Zige tangco catchment, the palaeolakes occupied 272km 2 and 246km 2,respectively, with lake levels being 10m and 8m higher than the present; for the same periods, the palaeolakes in the Coe catchment, which is at the southeast of Zigetangco catchment, had areas of 220km 2 and 138km 2, respectively, being 30m and 12m higher than the present.Using Kutzbach's equation of energy balance to compute land evaporation and water surface evaporation with step-after-step approaching method to obtain the parameters, and modeling the combined hydrological and energy balance of Zigetangco and Coe basins, the following estimates of precipitation were yielded: (400±20)mm/a at 24kaB.P. and (370±20)mm/a at 9.0-6.0kaB.P.,in Zigetangco catchment, and (535±20)mm/a at 24kaB.P. and (470±20)mm/a at 9.0-6.0kaB.P., in Coe catchment, respectively.