Winter and summer monsoonal evolution in Gonghe Basin,northeastern Qinghai-Tibetan Plateau since the Last Glacial Maximum

摘要

Geochemical and grain size analysis on the DQ (Dongqi) profile from Gonghe Basin, northeastern Qinghai-Tibetan Plateau, indicates that regional climate has experienced several cold-dry and warm-wet cycles since the last glacial maximum (LGM). The cold and dry climate dominated the region before 15.82 cal. ka B.P. due to stronger winter monsoon and weaker summer monsoon, but the climate was relatively cold and wetter prior to 21 cal. ka B.P.. In 15.82-9.5 cal. ka B.P., summer monsoon strength increased and winter monsoon tended to be weaker, implying an obvious warm climate. Specifically, the relatively cold and dry condition appeared in 14.7-13.7 cal. ka B.P. and 12.1-9.5 cal. ka B.P., respectively, while relatively warm and wet in 13.7-12.1 cal. ka B.P.. The winter and summer monsoonal strength presents frequent fluctuations in the Holocene and relatively warm and wet conditions emerged in 9.5-7.0 cal. ka B.P. due to stronger summer monsoon. From 7.0 to 5.1 cal. ka B.P., the cycle of cold-dry and warm-wet climate corresponds to frequent fluctuations of winter and summer monsoons. The climate becomes warm and wet in 5.1-2.7 cal. ka B.P., accompanying increased summer monsoon, but it tends to be cold and dry since 2.7 cal. ka B.P. due to enhanced winter monsoonal strength. In addition, the evolution of regional winter and summer monsoons is coincident with warm and cold records from the polar ice core. In other words, climatic change in the Gonghe Basin can be considered as a regional response to global climate change.