河西走廊花海古湖泊早、中全新世湖水盐度变化及其环境意义

通过对花海古湖泊沉积剖面8.42~0.405 m沉积物样品的矿物和化学元素测定，分析了沉积物中盐类矿物含量及化学元素K/Na比值的变化情况，结合已有的年代地层结果，重建了花海古湖泊10.47~5.5 cal ka BP湖水盐度变化. 结果表明：花海湖泊全新世湖相沉积阶段中，除个别层位以硫酸盐类矿物沉积为主外，早全新世(10.47~8.87 cal ka BP)和中全新世(8.87~5.5 cal ka BP)均以碳酸盐盐类矿物沉积为主，并且早全新世时期K/Na高于中全新世时期，揭示了早全新世时期湖水盐度高于中全新世时期. 这一结果与该湖泊沉积过程所揭示的湖泊水位变化、粒度等揭示的有效湿度变化具有一致性，表明花海湖泊早、中全新世湖水盐度的高低可以指示其湖泊水位的变化，并间接反映了有效湿度的变化. 结合花海湖泊晚全新世湖泊萎缩、气候干旱的特点，该区域早、中、晚全新世气候干湿变化变化模式可以概况为早全新世降水增强、气候呈现由干向湿的转变，中全新世有效湿度最大，晚全新世气候干旱. 这种全新世气候干湿变化模式有别于西风区，亦与季风区不完全相同，呈现出了一种季风-西风过渡带全新世气候干湿变化的模式.

The Salinity Change and Its Environmental Significance in Huahai Lake,Hexi Corridor,Northwest China During the Early-Middle Holocene

Carbonate mineral and sulfate mineral composition changes during the Holocene in Huahai Lake were reconstructed using X-ray diffraction, and the K/Na change was reconstructed using X-ray fluorescence. Then, the lake water salinity change was reconstructed during 10.47-5.5 cal ka BP in Huahai Lake. The results showed that carbonate mineral was the main mineral deposition in the lake sediments during the early (10.47-8.87 cal ka BP) and middle Holocene (8.87 - 5.5 cal ka BP), except for some particular layers. In addition, K/Na ratio was higher in the early Holocene which indicated that lake water salinity in 10.47-8.87 cal ka BP was higher than that in 8.87-5.5 cal ka BP. It suggested that the water salinity change was consistent with lake level and effective humidity change during the early and middle Holocene, and the water salinity indicated the change in effective precipitation. In addition, combined with the lake dried up, which indicated that the climate became arid during the late Holocene, one can see that Holocene environmental change in Huahai Lake as follows: climate shifted from arid to humid in the early Holocene, and was most humid in the mid-Holocene and arid in the late Holocene. This pattern is different from Asian monsoon areas and westerly areas, showing that the monsoon-westerly transition zone is not only controlled by the Asian monsoon but also affected by westerly winds.