Geochemical evidences of dry climate in the Mid-Holocene in Gonghe Basin, northeastern Qinghai-Tibetan Plateau

Abstract

Previous research on climatic change in the Mid-Holocene in China indicates that it was a warm and humid period, accompanied by stronger summer monsoons, and it is defined as the Megathermal in the Holocene, or the Holocene Optimum period. However, this conclusion is mainly directed at the monsoonal region in eastern China. In this research, we chose the Gonghe Basin in the northeastern Qinghai-Tibetan Plateau as the study area. Geochemical analysis of the profiles of paleosols and aeolian sand in the Santala area in the middle of the Gonghe Basin, along with OSL (optically stimulated luminescence) dating, indicates that the regional climate has experienced several warm-humid and cold-dry cycles since 11.8 ka. In particular, the Mid-Holocene (8.1–4.6 ka) was relatively cold and dry as evidenced by drastic fluctuations in chemical weathering degree and humidity, a higher aridity index, and sparse vegetation, accompanying increased winter monsoonal strength. In order to clarify whether this is an individual or local signal, we compared our geochemical analysis results with lake and peat records and aeolian deposits of the monsoonal boundary region. The results indicate that the climate deteriorated widely, with declines in temperature and moisture, in the Mid-Holocene in the modern monsoonal boundary zone. Furthermore, the duration of climate deterioration (relatively dry period) generally decreased from west to east in the aforementioned regions. Therefore, this dry phase in Gonghe Basin may be representative of dry events in Mid-Holocene in northern China. In addition, we discuss the reasons for this dry climate from several perspectives: (1) it probably can be attributed to a decline in summer monsoonal strength; (2) the regional evaporation loss (forced by high temperature) was not compensated by regional precipitation; (3) the thermal dynamic effect of the Qinghai-Tibetan Plateau.