海洋沉积物中生物成因Ba的海洋生产力研究

REVIEW ON OCEAN PRODUCTIVITY BY USING BIOGENIC BA IN MARINE SEDIMENTS

一直以来,对海洋古生产力的研究是古海洋学研究领域中一个非常重要的分支,因而寻求反演海洋古生产力替代性指标成为了海洋工作者的首要任务。沉积物中有机碳、钙质生物、硅质生物及其碳、氧同位素组成等经典的海洋生产力指标早已确立,但这些与浮游生物直接相关的替代指标因其在海底沉积物中低的保存率,限制了它们在广阔海域中的应用。一些与生物成因相关的地球化学指标(Ba,P,Al,U等),其在海洋中独特的生物地球化学性质使得它们成为定性、定量指示海洋古生产力强有力的手段,尤其是生物成因Ba,在富氧沉积环境中可达30%左右的保存率,是重建海洋生产力最有前景的替代指标。利用单一的生物成因Ba,或结合其他指标,在国外已经成为研究海洋古生产力的重要方法。文章在阐述Ba作为古海洋生产力指标的发展、计算以及影响因素等问题的基础上,进一步描述了其应用现状以及南海生物成因Ba的初步研究状况。南海沉积物ODP1148站岩芯中生物成因Ba的初步研究表明,Ba与Ca含量具有较好的相关性,在我国南海北部中中新世以来以Ba作为古生产力替代指标具有较大的潜力,但在方法的利用上还需进一步研究。如果要获得更加准确的古海洋环境信息,综合分析多个替代性指标会更加可靠。

Paleoproductivity is an essential topic in paleoceanography studies. The key point is to seek reliable proxies for paleoproductivity reconstruction. The classic proxies, for example, organic carbon, calcareous and siliceous organism and their carbon, oxygen isotope compositions, have been broadly applied to indicate paleoproductivity changes. These proxies,however,generally have very low preservation rates in sediments,which make their paleoproductivity interpretations ambiguous. More recently, some biogenic geochemical proxies, such as Ba, P, Al, U, are applied to qualitatively or quantitatively which indicate paleoproductivity changes. Among these proxies, biogenic Ba, has becomes the most promising proxy for it＇s high preservation rate, up to 30% in sediments, compared with less than 1% for organic carbon and 5% for biogenic silica. Using single biogenic Ba or coupling with some other proxies has been considered a powerful tool to research paleoproductivity,but it seldom applies to our marginal sea. In this article, we review the development,calculation methods, influence factors and research status of Ba as ocean productivity proxy, and further state the application in China marginal sea. Preliminary research of biogenic Ba on sediments at ODP 1148 site in South China Sea suggests that Ba could be a reliable paleoproductivity proxy in the Northern SCS since middle Miocene, which show a good correlation between concentration of CaCO3 and biogenic Ba during 0 - 14Ma. To a certain extent, there is need to further research the method of how to get biogenic Ba because of much terrigenous material inputted to marginal sea. Any proxy has it limitation, so, synthetically combination of several proxies will help to obtain more reliable reconstructions for paleoproductivity in the SCS or other sea area.