16 ka以来冲绳海槽中南部有机质来源及其对上升流演变的指示

摘要

基于14C测年,通过对OKT12孔有机碳、氮含量及碳同位素、粒度等指标的分析,探讨了16ka以来冲绳海槽中南部有机质来源及其对上升流演变的指示.研究发现,TOC堆积速率、δ13C和TOC/TN比值等指标呈明显的三阶段变化.陆源C3植物、海源浮游生物以及台湾河流悬浮体是OKT12孔有机质的3个主要端元.δ13C和TOC/TN比值物源判别显示,低海平面时期(16～ 10 ka),OKT12孔有机质主要来自陆源输入和海源浮游生物的贡献;10～7 ka阶段主要来自台湾河流悬浮体贡献,反映了早全新世以来黑潮的加强;高海平面以来(7～0 ka),OKT12孔有机质以海源浮游生物贡献为主,其变化反映了上升流的强弱波动.7～4 ka海洋浮游生物贡献量的增加指示上升流增强,4 ka以来贡献量减少指示上升流减弱.上升流变化与黑潮强弱、流轴位置变动有关,两者受到高频气候事件ENSO活动控制.%The core OKT12,mainly consist of clayed silt,was collected in the middle south Okinawa Trough(26.05°N,125.34°E;water depth 1924.53 m).AMS 14C age results revealed that core OKT12(length 4.68 m) recorded the environment change since 16.3 ka,with volcanic ash seen at 6.8～7.3 ka.Kuroshio Current,the most important current in the research area,controlled ocean environment and transport of Taiwan material.TOC,TN content and organic carbon isotope analysis were conducted to discuss source of organic matter in the middle south Okinawa Trough since 16 ka and its response to development of upwelling in the Late Holocene.Change of organic matter source inferred by TOC accumulation rates,δ13C and TOC/TN ratio was divided into three sections.Terrigenous C3 plant,marine plankton,and Taiwan river suspended sediment were the most important end-members of organic matter.Discrimination plots indicate organic matter of the core OKT12 was mainly from high terrestrial input and marine plankton when sea level was low (16 ～ 10 ka).During 10～7 ka,Taiwan river suspended sediment was main contributor,indicating strengthening of the Kuroshio Current.When sea level rose to high stand(7～0 ka),marine plankton controlled organic matter composition which indicated strengthening of upwelling intensity.Increasing marine plankton contribution indicated enhancement of upwelling during 7～ 4 ka.Since 4 ka,marine plankton contribution decreased when upwelling was weak.The strength of upwelling was related to intensity and position of the Kuroshio Current,which both might be affected by the high-frequency ENSO event.