CLIMATIC BACKGROUND OF MODERN COBICULA FLUMINEA AND THE STABLE ISOTOPES OF SHELLS FROM THE REPRESENTATIVE AREAS IN CONTINENTAL CHINA

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.