近60年来南黄海沉积物高分辨率敏感粒级对东亚冬季风的响应

对南黄海中部泥质区F306柱状样的沉积物进行分析,运用粒径—标准偏差法,得出该孔敏感粒级组分为23.10~65.30 μm (5.44Φ~3.94Φ),其粒级的含量15.6%~22.3%,平均粒径38.5~41.4 μm (4.70Φ~4.59Φ),证明敏感粒级可以作为东亚冬季风的高分辨率替代指标,进一步阐明了敏感粒级作为东亚冬季风替代指标在更高分辨率上的可行性。根据敏感粒级沉积记录,在1950—1986年期间,将东亚冬季风分为强—弱—强3个阶段,指示了该阶段东亚冬季风存在近10年的周期。1986/1987为近60多年来东亚冬季风由强变弱的转折点,与东亚气候变化具有较好的对应关系,首次在中国东部海域中记录了此逆转事件,认为1986年后沉积物敏感粒级的变粗可能与长江物源变粗、东亚冬季风的减弱以及夏季风增强有关。

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.