古海洋生产力指标研究进展

寻求反映古海洋生产力变化的指标是古海洋学研究的重要内容。生物沉积物、营养元素、微量元素和同位素、古生物资料等与古海洋生产力具有一定的关系,常用于古海洋生产力的重建工作:(1)生物沉积物主要包括有机碳、生物碳酸盐和生物硅质沉积等,其埋藏速率在很大程度上受到古海洋生产力的控制,常常用作古海洋生产力的替代性指标;(2)在地质时间尺度上,古海洋生产力主要受到大洋中营养元素可利用程度的控制,因此营养元素的相关记录可以提供古海洋生产力状况的重要信息;(3)海洋中某些微量元素的地球化学行为或者与有机质的改造有关,或者受到氧化还原条件变化的控制,或者受到某种浮游生物的生长的影响,从而能够直接或者间接地指示古海洋生产力的变化;(4)海相碳酸盐和有机质的碳同位素记录,海相有机物的氮同位素比值也用以再造古生产率等古海洋学参数;(5)可以利用对微体化石丰度值及其组合反映古生产力的变化。

Progress in the study of proxies of paleocean productivity

It is of importance to obtain proxies reflecting the fluctuations of primary productivity in paleoceanographic studies. Biological sediments, nutrients, trace elements, isotopes and paleontological data, commonly show some relationship with the marine production. Therefore, they could be used to reconstruct paleocean productivity. The accumulation rates of biological sediments, including organic carbon, biogenetic carbonates and deposition of siliceous sediments. These are often dominated by paleocean productivity, so that these sediments can be used as the productivity proxies. Oceanic production, on the geological timescale, may be controlled by the availability of nutrients in the ocean. The nutrition records could still give much information to the prolificacy of the paleocean. The geochemical behavior of certain trace elements might either be related to the remineralization of organic matter, or controlled by the redox status in the bottom water, or affected by the growth of some plankton. Consequently, the abundance or ratio of these elements may indicate, directly or indirectly, the variations in paleoproductivity. Paleoproduction could be obtained from the carbon stable isotopic records of marine carbonates and organic matter, and nitrogen isotopic ratios in the marine organic matter. The abundances and assemblages of microfossils can be utilized to reflect the variations of paleoproductivity.