南海深海盆表层沉积物氮的地球化学特征与生态学功能

Geochemical characteristics and ecological functions of nitrogen in the abyssal basin surface sediments,South China Sea

研究了南海深海盆区域(南沙海槽西南部)表层沉积物中氮的形态、分布及其在生物地球化学循环中的功能.研究表明,表层沉积物中不同形态氮的含量不同.其中,氧化还原转化态的氮(SOEF-N)含量最高,平均为68.3μg/g,占总氮(TN)的7.08%;弱酸转化态氮(WAEF-N)含量最小,仅占总氮(TN)的1.09%.离子交换态(IEF-N),WAEF-N,S OEF-N及TN的地球化学分布特征存在一定相似性:均由海槽东西两侧向中央递增,并在槽底呈高含量分布;SAEF-N(强碱转化态)分布则与该趋势相反.IEF-N,SAEF-N和SOEF-N的分布主要受沉积物中有机碳含量(OC)控制;而WAEF-N则与碳酸盐(CaCO3)存在显著的负相关关系;TN与OC不具有显著意义的相关,间接说明二者来源的不同.同时,各形态氮的分布还与沉积物粒度类型密切联系.此外,研究区域内由沉积物提供的氮源很大程度上补偿了浮游植物对水体中营养盐的消耗,对维持该海域的初级生产力水平起到一定作用.其中,IEF-N和SOEF-N的释放对浮游植物生长及初级生产力的贡献较为显著.

The abyssal basin of the South China Sea（southwestern Nansha Trough）, one of the most productive areas of the southern South China Sea, is a typical semi-deep sea area and forms the transition from the shoal water zone to the abyssal zone. In order to understand the roles and distributions of nitrogen in the biogeochemical cycling in this area, the quantities of various nitrogen forms and total nitrogen content （TN） in surface sediments were experimentally quantified during a cruise in April - May 1999. The quantities of various nitrogen forms in surface sediments of the study area were different： nitrogen in ion exchangeable form （IEF-N） 11.4～35.8μg/g, nitrogen in weak acid extractable form （WAEF-N） 4. 4～23.1μg/g, nitrogen in strong alkali extractable form （SAEF-N） 10.4～29.3μg/g and nitrogen in strong oxidation extractable form （SOEF-N） 15.4～218.3μg/g. The distribution characteristics of the various nitrogen forms （except SAEF-N） and TN were to some extent similar with the relatively low nitrogen contents observed on the Kalimantan continental slope （KCS） in the east and Nansha oceanic plateau （NOP） in the west of the study area, thus forming high values in the trough area. It was controlled by organic carbon contents （OC） and carbonate contents （CaCO3） in sediments as well as by the sediment grain size. Four forms of extractable nitrogen in surface sediments could be released and participated in biogeochemical recycling. When all the four forms of extractable nitrogen were released to take part in recycling, IEF-N and SOEF-N were the predominant contributors to phytoplankton and primaryproductivity in water column.