The Last 13,000 Years, The Environmentally Sensitive Zone Monsoon Climate Change And ~ (14) C Chronology

The climatic reversal event that occurred during the transition from Pleistocene (last glacial cycle) to Holocene (post glacial) conditions in east Asian environmentally sensitive monsoon zone can be viewed as a historic analog for the future. It is useful for the prediction of possible future trend toward climatic change in east Asia with the arrival of global warming caused by the increases in the proportion of greenhouse gases in the atmosphere. In order to explore this concept, the author has chosen high-resolution peat, loess-paleosol and eolian-paleosol sequences from desert-loess transition belt which is a part of the sensitive inland environment zone and its neighboring regions in China for a comprehensive study. Through nearly 100 ¹⁴C AMS determinations , several thousand proxy data points gained fromδ¹³C determinations and % carbon content of organic sediments, pollen analyses, grain size analyses, magnetic susceptibility determinations, and the consequent establishment of chronological sequences, the nature of the east Asian monsoon climatic reversal event (The Younger Dryas event) before the warm Holocene arrival, could be studied. This event was characterized by monsoon climatic oscillation from cold-dry to cold-wet then return to cold-dry conditions. Furthermore, the east Asian monsoon climatic instability during the last deglaciation has been discussed. The significant variability within monsoon precipitation events during the last deglaciation event or even Younger Dryas is related to the interaction between cold air mass from the Siberian-Mongolian high pressure zone with warm, humid air masses from the ocean.Stratigraphic and paleoclimatologic studies have been combined with¹⁴C chronological determinations in order to establish a record of monsoon variation over the last 30,000 years, with emphasis on the last 13,000 years. The author concludes that the last deglaciation climate variation in the proxy records for the east Asian monsoon has an asymmetric shape; the warming events are abrupt and the cooling events are gradual. Century or millennium scale event cannot be explained by Milankovich theory, but can be regarded as a non-linear response to climate change driven by orbital parameters.The stratigraphic sequences of Loess Plateau, desert/loess transitional zone covering the last 30,000 years have been subdivided into 6 climatic stratigraphic units. The stratigraphic sequences covering the Younger Dryas period has been further divided into Heheize silt, Baxie paleosol and Taohe loess. Moreover, it is suggested that the Pleistocene/Holocene boundary be placed at 10,000¹⁴C years BP in North China, from the point of view of paleomonsoon change.