青海湖表层沉积物介形虫丰度及其壳体氧同位素的气候环境意义

CLIMATIC AND ENVIRONMENTAL SIGNIFICANCE OF OSTRACOD ABUNDANCE AND THEIR SHELL OXYGEN ISOTOPE FROM LAKE QINGHAI SURFACE SEDIMENTS

介形虫已被广泛应用于湖泊古环境变化研究中。通过对青海湖东南湖盆一表层沉积岩心的介形虫壳体丰度(介壳总丰度、意外湖花介壳体丰度和胖真星介壳体丰度)、介壳氧同位素、总碳酸盐含量及其氧同位素等多指标的高分辨率对比研究,结合前人研究成果发现,最近五百多年青海湖东南湖盆沉积物中介形虫仅有两个种:意外湖花介和胖真星介,且以意外湖花介为主,胖真星介较意外湖花介更喜盐耐盐;总碳酸盐氧同位素较介壳氧同位素偏轻,这可能是二者形成时的季节、水深以及微环境等方面的差异造成,并发现部分段落介壳氧同位素与总碳酸盐氧同位素存在相位差。介壳丰度、介壳氧同位素、总碳酸盐含量及其氧同位素在整个序列上有一致的变化,对湖水盐度变化有很好的响应,反映了湖区有效湿度的变化。在此基础上重建了最近五百多年来青海湖5个大的干湿变化阶段。

Ostracods have been widely used in the lacustrine palaeoenvironment reconstruction. Multi-proxies, including ostracod abundance （TAOST, TALi and TAEm）, ostracod shell oxygen isotope （δ^18OOST）, total inorganic carbonate content （TIC） and its oxygen isotope （δ^18OTIC） are examined for a short core from the southeastern basin of Lake Qirlghai. Together with the former researches, the result shows that in the past -560 a there were only two species, Limnocythere inopinata and Eucypris rnareotica ,survived in the lake. Their abundance indicates the changes in salinity. There exists a systematic difference between δ^18OOST and δ^18OTIC, with the latter more negative, probably due to their difference in formation time （seasonal difference）, water depth and/or microenvironment. Furthermore,in some sections the δ^18OOST changes earlier than δ^18OTIC. All the proxies show a covariance trend, responding to the changes in water salinity and partly in the effective humidity of the lake area. Based on these proxies, five dry-wet phases are re- constructed for the past -560a in Lake Qinghai. It should be noticed that the discussion and results are just limited to one sediment core in the southeastern basin of Lake Qinghai. The environmental significance of these proxies and their relationship need further systematic researches spatially and temporally.