南冲绳海槽7000aB.P.以来基于长链不饱和烯酮指标的古海洋生产力变化及其与气候的关系

古生产力的精确重建对于了解地质历史时期的碳循环具有非常重要的作用,高分辨率有机地球化学记录在重建古海洋生产力上有独到的优势。基于17个AMS14C年代分析数据,本文分析了冲绳海槽南端MD05-2908孔(24°48.04′N,122°29.35′E)沉积柱状样中的长链不饱和烯酮含量以及物质通量,并结合沉积物有机碳同位素数据恢复评价了南冲绳海槽古海洋生产力的变化。结果显示近7000aB.P.以来南冲绳海槽古生产力存在着显著波动。将海洋古生产力指标与全新世ITCZ南北移动记录的对比分析,发现其变化与ITCZ的南北移动有密切的关系,一方面ITCZ南北移动影响陆源物质的输入,从而改变海洋营养物质的供应状况,造成生产力的高低变化;另一方面,ITCZ南北移动所造成的陆源物质输入冲淡了海洋生产力输入对沉积有机质的贡献,因此在高陆源物质影响区单用生物标志化合物相对有机碳的丰度评价古海洋生产力存在着一定的不可靠性。此外,通过与高纬度气候记录的对比发现,南冲绳海槽海洋生产力的低值变化与北半球高纬度地区的气候冷事件基本一致,显示出高低纬度气候环境变化之间的强相关性。

PALEOPRODUCTIVITY VARIATION AND ITS CORRELATION WITH CLIMATE CHANGES:AN APPROACH OF LONG-CHAIN ALKENONE

The accurate reconstruction of paleoproductivity is critical for understanding the carbon cycle in the past and for predicting the fate of anthropogenic carbon in the future.Biomarkers in marine sediments are useful tools for paleoenvirionment study and have been used as proxies for total and specific phytoplankton group paleoproductivity.Based on 17 AMS14C age controlling points,we report here molecular abundance data for alkenone and organic carbon isotopic data for bulk samples from a giant piston core MD05-2908(24°48.04'N,122°29.35'E).The aim is to evaluate the paleoproductivity and interpret the climatic-induced controlling factors for the past 7000aB.P.The results showed that the paleoproductivity in the South Okinawa Trough(SOT)fluctuated frequently in the past 7000aB.P.By correlating with the Titanium records from Huguang Marr and Cariaco Basin,we found out that the paleoproductivity was largely controlled by the latitude migration of ITCZ.The rapid southward shift of the ITCZ might have caused longer staying of the rainfall front in the source supply area,thus,led to intensified erosion,brought increased terrigenous material into the ECS and SOT by fluvial the terrigenous materil delivers to the SOT.Terrigenous input on the one hand might have fertilized the sea surface of SOT and stimulated the production,but on the other hand might have diluted the signal of marine derived input to the sediments.The lower production periods in the SOT correlated well with those ice-drift episodes recorded in the high latitude Atlantic Ocean,suggesting the strong relationships between high and low latitude climate.