湖泊沉积物介形虫碳酸盐clumped同位素与古温度定量/半定量重建

Ostracod cultivating experiments will be carried out under different temperature conditions using the water and live ostracods from Sugan Lake in Qaidam basin。Clumped isotope Δ47 - temperature relationship for the ostracod valves in the lake will be established based on the cultivating experiments and the compare of the clumped isotope Δ47 of the ostracod valves in the surface sediments deposited in the last several decades and the meteorological temperature. On the basis of the established clumped isotope Δ47 - temperature relationship for the ostracod valves, the temperature variations during the last 2000a will be quantitatively/semi-quantitatively reconstructed through the analysis of the clumped isotope Δ47 of the ostracod valves of the sediment cores. Oxygen isotope composition of lake water will be achieved using the Craig paleotemperature equation, combined with the oxygen isotope composition of ostracod valves and the reconstructed temperature. Then the humidity variations in the lake area will be inferred from the lake water oxygen isotope composition. Accordingly, the property, time, variation amplitude and tempo of the main climate events will be revealed. This study will provide the basic data for the compare of regional and global climate change and for the driving mechanism research, and will be helpful in predicting the future climate change. This study will provide a new way for quantitative/semi-quantitative palaeoclimate reconstruction, and will extend the research and application of clumped isotope.

利用柴达木盆地苏干湖湖水和介形虫活体开展不同温度条件下介形虫培养实验，结合苏干湖近几十年来表层沉积物介形虫壳体碳酸盐clumped同位素Δ47与温度记录的对比研究，揭示介形虫Δ47对温度变化的响应关系，研究建立湖泊介形虫壳体碳酸盐Δ47与温度的转换函数。在此基础上通过对沉积物柱芯不同沉积时段介形虫Δ47值的研究，定量/半定量恢复湖水古温度变化，结合介形虫氧同位素研究重建湖水氧同位素组成变化历史，推断湖区干湿变化，揭示该地区近2000a来主要气候变化事件的性质、时间、幅度和速率，为区域和全球气候变化对比及驱动机制研究提供基础性资料，为合理预测未来可能出现的气候变化提供借鉴。 本研究将为定量/半定量古气候重建提供新的途径，同时将丰富和拓展clumped同位素的研究和应用。

使用UWITEC钻在苏干湖成功获取到2根沉积物柱芯，长度分别为4.68m和4.76m，纹层定年结果显示该沉积柱芯记录了过去2200多年来的沉积历史。通过对苏干湖沉积物碳酸盐clumped同位素及碳氧同位素、粒度及XRF元素分析，重建了苏干湖流域过去两千多年来的气候变化。并对湖泊沉积物碳酸盐clumped同位素的温度指示意义及应用进行了分析。.研究结果显示苏干湖沉积物碳酸盐Δ47值重建的温度为碳酸盐生长累计平均温度，主要反映苏干湖湖盆5-9月平均气温。通过湖泊表层水体温度与大气平均温度转换公式计算得到：近2000年来苏干湖流域5-9月的平均气温为20.7℃，其中近800年来平均气温为20.5℃，200 BC-1200 AD期间平均气温为21.0℃。近800年来平均气温较200 BC-1200 AD期间降低0.5℃。.通过多指标综合分析发现，苏干湖流域过去2000多年来存在两个较干旱时期，即280 AD-940 AD和1680 AD-1800 AD；最温暖的时期为800 AD-1200 AD，最寒冷的时期为1640 AD-1760 AD，正好分别与“中世纪暖期”和“小冰期”对应。与clumped同位素分析结果一致。综合分析表明，在“中世纪暖期”前期，气候以“暖干”为主要特征；在“中世纪暖期”后期，气候以“暖湿”为主要特征。在“小冰期”期间，气候以“冷干”为主要特征。