Abstract: 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.

Key words: organic carbon isotope, comparative study, Lanzhou area, Jianghan Plain