RESPONSE OF SENSITIVE GRAIN-SIZE TO EAST ASIAN WINTER MONSOON FOR PAST 60 YEARS IN THE MUD AREA OF WESTERN SOUTH YELLOW SEA

The study of the Core F306 has made it possible to acquire a resolution up to 1.5 years for the muddy deposits of the South Yellow Sea (SYS). The sensitive grain size population of the core is 23.10-65.30 μm(5.44Φ-3.94Φ), with a mean grain size of 38.5-41.4 μm(4.70Φ-4.59Φ) and the content ranges from 15.6 to 22.3 percent. The results illustrate that the sensitive grain-size fraction can be used as a sedimentary proxy to reconstruct the evolution of the East Asian Winter Monsoon (EAWM) at a higher resolution. Based on the changes in sensitive grain-size, the evolution of EAWM is divided into three stages (strong-weak-strong) during 1950—1986, revealing a cyclic change every 10 years. 1986/1987 is the turning point of EAWM from strong to weak in the recent 60 years, and this is a well responding to the East Asian climate change. From 1986 to 2007, the sensitive grain-size is mainly influenced by median grain size of the Yangtze River sediments, reflecting human impacts on the sediment records. The enhancement of East Asian Summer Monsoon and weakening of East Asian Winter Monsoon have also made contributions to the grain size coarsening.