近3000cal.aB.P.以来东海东北部环境异常及其与全新世ElNiño活动的可能联系

利用取自东海东北部、冲绳海槽西侧陆坡的重力柱状岩芯DOC082（29°13.93′N,128°08.53′E;水深1128m）,通过对碳酸钙、有机碳和蛋白石等生源组分含量的分析,结合浮游有孔虫、底栖有孔虫、放射虫和硅鞭藻等微体古生物化石丰度的变化以及底栖有孔虫属种组成特征,揭示了全新世东海东北部生物生产力的演变。研究结果显示,近10500cal.aB.P.以来生源组分含量和微体古生物化石丰度的演变趋势十分相似,明显分为3个阶段:约4000cal.aB.P.之前的早、中全新世明显偏低,大约在4000cal.aB.P.左右开始突然大幅度上升,而约3000cal.aB.P.以来的晚全新世以持续的高值为显著特征。生源组分含量、微体古生物化石丰度以及底栖有孔虫内生属种Uvigerina和Bulimina百分含量等指标的变化一致指示,东海东北部近10500cal.aB.P.以来古生产力演变的显著特征是早、中全新世明显偏低,约4000cal.aB.P.左右突然且大幅度上升,大约3000cal.aB.P.之后的晚全新世为生物生产力异常的高值期;同时有研究表明该区域的表层海水年平均温度（SST）也呈现了明显的三段式演变:早全新世10500～8400cal.aB.P.期间为持续的高值期、中全新世SST相对稳定、3100～500cal.aB.P.期间的晚全新世为显著的低SST时期1]。近3000cal.aB.P.以来古生产力的异常高值和表层海水古温度的大幅度下降说明晚全新世区域海洋环境发生了明显的改变。据东海东北部现代生物生产力和表层海水温度的分布特征和控制机制、结合现代ElNio发生期间中国大陆气候和降水异常以及黑潮暖流变异的分析表明,近3000cal.aB.P.来东海东北部的环境异常可能是对晚全新世ElNio活动显著增强的反应。

THE ENVIRONMENTAL ANOMALIES IN THE NORTHEASTERN EAST CHINA SEA SINCE ABOUT 3000cal.aB.P.AND ITS POSSIBLE RELATION TO EL NI(N)O ACTIVITY IN THE HOLOCENE

Based on a gravity core DOC082,retrieved from the western slope of Okinawa Trough in the northeastern East China Sea(ESC)(29°13.93'N,128°08.53'E;1128m water depth),through analyses of biogenic compounds such as carbonate,organic carbon,and opal,and incorporating with micropaleontological proxies(the abundance of planktonic foraminifera,benthic foraminifera,radiolarian,and silicoflagellate)and the compositional characters of benthic foraminifera fauna,the productivity changes during the Holocene in the northeastern ESC were reconstructed.Results indicate that the changes of biogenic and micropaleontological proxies display some similarities through the last 10500 years,which show three different phases:Lower values are recorded during the Early and Middle Holocene(before about 4000 cal.aB.P.),which is followed by an abrupt and remarkable increase at about 4000 cal.aB.P.The Late Holocene(after about 3000 cal.aB.P.)is characterized by continuously high values.The multi-proxy data of paleoproductivity and percents of benthic foraminifera genera(Uvigerina and Bulimina)show that during the Early and Middle Holocene productivity is relatively low with a sudden and distinct increase at about 4000 cal.aB.P.,and the Late Holocene is marked by abnormally high productivity.Also,down-core sea surface temperature(SST)estimates reveals that the changes of mean annual SST display a three-step trend:An Early Holocene continuous warming between 10500 cal.aB.P.and 8400 cal.aB.P.,a Middle Holocene relatively stable and high SST that lasts until 3200 cal.aB.P.and a Late-Holocene distinct SST decline which takes place between 3200 cal.aB.P.and 500 cal.aB.P.1].The enhanced biological productivity and distinct decline of sea surface temperature(SST)after about 3000 cal.aB.P.indicate that a major change of oceanographic conditions occurred in the northeastern ECS during the Late Holocene.After analyzing on the mechanism of modern productivity and SST changes in the northeastern ECS,and based on the climate and precipitation anomalies in the Chinese continent and variations of the Kuroshio warm Current during modern ElNio phenomenon,we suggest that the anomalous environmental conditions in the northeastern ECS may imply an intensified ElNio activity during the Late Holocene.