青海湖沉积物有机碳含量与同位素和粒度特征及其古气候意义

CHARACTERS OF THE TOTAL ORGANIC CARBON AND ORGANIC CARBON ISOTOPE AND GRAIN SIZE AND PALEOCLIMATE SIGNIFICANCE IN QINGHAI LAKE SEDIMENTS

对青海湖沉积物中粒度参数、总有机碳 (TOC)含量及其 δ1 3C值的形成条件与环境气候的关系进行了研究。结果表明 :在暖湿时期 ,沉积物中有机碳含量 (TOC)较高 ,有机质的 δ1 3C值较高 ,沉积物的平均粒径较细 ;反之 ,在冷干时期 ,沉积物中有机碳含量 (TOC)较低 ,有机质的 δ1 3C值较低 ,沉积物的平均粒径较粗。反映出沉积物中 TOC含量、有机质 δ1 3C值及粒度特征与气温具有良好的相关性。结合 1 4C测年 ,分析了湖区古气候演化序列 ,表明自 85 0 0 a BP以来湖区气候经历了 4个演化阶段

Qinghai Lake is the largest inland saline lake in China. Its sediments contain a large amount of information on paleoclimate environment changes.The organic carbon isotope (δ 13 C) in the sediments has been taken as an ideal sample for getting such information in the high cold semiarid areas because of its sensitivity to the climate changes. By the analysis of the characteristics of organic matter TOC and δ 13 C values and sediment grain size from samples of Qinghai Lake, paleoclimate changes are discussed in the paper. The results show that the organic carbon isotope and total organic carbon and grain size have a good relation with climate changes. During warmer and wetter climatic episodes, the values of δ 13 C and TOC of the organic materials in sediments are higher. On the contrary, during colder and dryer climatic episodes, the values of δ 13 C and TOC contents in sediments are lower . In addition, the sediment grain size provides a new effective way for recovering the climate changes. With the variation of the grain size from coarse to fine, the climate are changing from dry to wet. Further study has reconstructed the evolution sequence of paleoclimate in Qinghai Lake region since 8 500 aBP. It has four stages as follows. 8 500～5 300 aBP (depth 350～216 cm): the climate was warm and wet; during this stage there was a higher lake level; 5 300～3 100 aBP (depth 216～116 cm): the climate was cool and dry; the lake level descended; 3 100～2 000 aBP (depth 116～70 cm): the climate was warm and wet; the lake level unchanged; Since 2 000 aBP (depth 70～0 cm): the climate was cold and dry, the lake level was lower.