Oxygen isotopes in lacustrine carbonates of West China revisited: implications for post glacial changes in summer monsoon circulation

Five lakes in the Qinghai-Tibet Plateau and North Xinjiang have provided oxygen isotope records covering the past 17-11 cal. kyr BP. The modern lakes are first presented within the major atmospheric circulation and climate patterns of China, with the climate-related isotope composition of input water. Equations used to extract hydrological and climatic information from delta(18)O in carbonates are then given. After a discussion on potential causes for delta(18)O changes. each of the five isotope profiles is interpreted in the light of its specific environmental data. The most significant event observed in all records occurred at 12-11 cal. kyr BP: an abrupt intensification of summer rainfall associated with an extremely rapid 1000-1500 km westward migration of the monsoon fronts. The monsoon regime weakened in stages after 8-7 cal. kyr BP. Holocene maximal aridity is recorded at all sites between about 4.5 and 3.5 cal. kyr BP. Long-term changes in monsoon strength as inferred from our isotopic interpretation are in good agreement with climate model reconstructions in the Tibet-Qinghai Plateau, while observed hydrological changes in North Xinjiang are not simulated by the models. Also, the non-linearity of the Holocene monsoon variations cannot be accounted for by orbital forcing. (C) 1999 Elsevier Science Ltd. All rights reserved.