兰州与江汉平原有机碳同位素的古气候指示意义对比研究

选择以干冷气候为主的兰州和温暖湿润的江汉平原作为研究区域，结合其他多种指标和研究区的岩性特征，对有机碳同位素δ13Corg的古气候指示意义进行了初步探讨。结果表明，在兰州地区，δ13Corg值波动反映C3/C4植物比例的改变，指示温度变化。δ13Corg值偏正时，表明C4植物含量较大，反映温度较高，而δ13Corg值偏负时，表明气候较冷；江汉平原δ13Corg值主要反映降水信息， δ13Corg值偏负时指示相对暖湿气候，δ13Corg值偏正反映气候偏干。δ13Corg等指标同时还揭示了末次盛冰期以来两地古气候类同特征：即12.0 ka BP之前气候相对偏干；在全新世晚期，气候波动中转暖。不同之处表现为：约在12.0~10.0 ka BP，当兰州气候还很干冷时，江汉平原已进入暖湿的冰后期；而在全新世早中期，当兰州气候转为暖湿时，江汉平原气候则表现为略偏干。

PALEOCLIMATIC IMPLICATIONS OF LANZHOU AND JIANGHAN PLAIN: A CLIMATE PROXY STUDY OF ORGANIC CARBON ISOTOPE

Regarded as a sensitive indicator to paleoclimatic change, the organic carbon isotope in loess and lake sediments is widely used to reflect paleoclimatic condition and paleoenvironmental evolution. By combining analysis of other proxies, this paper is to explore the implication of organic carbon isotope in Lanzhou which is typical of dry and cold climate setting and Jianghan Plain of warm and moist environment. The results show that the significance of organic carbon isotope is different according to the diversities of carriers. In Lanzhou, the δ13Corg values represent the ratios of C3 to C4 plants and reflect the changes of temperature. The higher and lower values of δ13Corg in sediment are the result responsible to warmer and colder paleoclimates, respectively. In contrast, the values of δ13Corg in Jianghan Plain can indicate the varieties of rainfall. With the variation of δ13Corg value from high to low, the climate changes from dry to wet. Further conclusions can be made based on the δ13Corg values together with other indicators. There are certain degree of similarities in paleoclimatic evolution in both areas. For instance, the drier climate before 12.0 ka BP and warmer environment with repetitious fluctuations in the late Holocene in Lanzhou and Jianghan Plain are analogous. Although 4 stages of paleoclimatic change can be recognized in both areas, the paleoclimatic evolutions are different. In general, the climate warming up in early Holocene is earlier in Jianghan Plain than in Lanzhou. In addition, the climate between 12.0 and 10.0 ka BP in Lanzhou area is characterized by dry and cold, while in Jianghan Plain it has evoved into the warm and wet interglacial epoch.