CLIMATIC BACKGROUND OF MODERN COBICULA FLUMINEA AND THE STABLE ISOTOPES OF SHELLS FROM THE REPRESENTATIVE AREAS IN CONTINENTAL CHINA
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摘要: 根据实地考察和对现有资料的统计与分析,揭示中国大陆河蚬现生种主要分布在中国东南部年降水量大于800 mm (800~1 400 mm)、1月平均气温大于0℃(0.5~4.5℃)、温暖湿润的淡水-微咸水河湖环境之中。河蚬壳体在生长过程中记录了气候环境和水体性质的信息。利用碳酸盐自动装置与Finnigan MAT-253型质谱仪联机对河蚬壳体δ18O和δ13C的值进行了系统测试,通过对比分析发现,壳体生长过程中由于生理效应和生态习性差异造成全壳的δ18O值变化较小,江苏一帆河、古黄河、江西绵江和云南滇池4个采样区(点)之间变化仅为1.4‰;河蚬壳体不同部位δ18O值记录了生长过程中的季节性温度变化;随纬度增高壳体δ13C值富集轻同位素组成,有变负的趋势;雨热同期气候环境下的一帆河、古黄河地区现代河蚬壳体碳氧同位素值在个体生长过程中变化位相非常相似,反映了壳体碳氧同位素值对气候环境的响应。Abstract: Field investigations and statistic analyses on the existing data reveal that the modern Cobicula fluminea lives in fresh-mesohaline river-lacustrine conditions under the warm-humid climate, with annual average precipitation more than 800 mm (800~1 400 mm) and the average January temperature over 0℃ (0.5~4.5℃) in southeastern continental China. The shell records the climate situation and water property and the environments during its growth. δ18O and δ13C of shells taken from different areas and measured by mass spectrometer Finnigan MAT-253 show that there is very small δ18O differences between the shells living in the same area and the different areas with the comparable climate-environmental background. For example, δ18O among the shells taken from Yifan River,abandoned Yellow River from Jiangsu Province, Mianjiang River from Jiangxi Province and Lake Dianchi from Yunnan Province is only around 1.4‰. δ18O in different layers in the same shell is one of the proxies of the seasonal temperatures. The average value of δ13C from various areas indicates that there exists a general trend of decrease along the latitudes. δ18O and δ13C values of shells from Yifan River and abandoned Yellow River in Jiangsu Province with a warm-humid season possess a similar change procedure, indicating that δ18O and δ13C are in immediate response to the regional climate changes.
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