海水硝酸盐氮、氧同位素组成研究进展

海洋中氮的生物地球化学循环影响着海洋生态系统的结构和功能,并和全球气候变化有着密切的联系,一直是海洋科学研究的重点和热点。海水硝酸盐的15N/14N和18O/16O比值可以反映海洋中氮循环的主要过程,因而成为研究海洋氮循环的一个重要手段。综述海水硝酸盐氮、氧同位素组成的测定方法,同化吸收作用、硝化作用、反硝化作用、生物固氮作用等氮循环过程所导致的氮、氧同位素分馏及其在海洋学研究中的应用。海洋生态系中硝酸盐氮、氧同位素的分布可以提供支持生物生产力的氮来源信息,以及氮在不同储库迁移转化的路径与机制。未来的研究需要发展适用于低含量硝酸盐的同位素测量方法,构筑海洋氮的收支平衡,掌握影响上层海洋硝酸盐氮、氧同位素变化的过程,获取全球海域有关硝酸盐氮、氧同位素组成的更多数据。

Progress in Nitrogen and Oxygen Isotopic Composition of Nitrate in Seawater

Marine nitrogen cycle plays a key role in marine biogeochemical cycles,which has its impacts on the structure and function of regional and global marine ecosystem,and is closely related to global climate change.Nitrogen and oxygen isotopes of nitrate reflect the major nitrogen transformation processes in the ocean,and become important tools in the study of marine nitrogen cycle.In this paper,we summarized recent progresses in the analysis of nitrogen and oxygen isotopes of nitrate in seawater,the isotopic fractionations during the major nitrogen cycling processes,i.e.assimilation of nitrogen nutrients,nitrification,denitrification,dinitrogen fixation,and their application in marine nitrogen studies.The distribution of nitrogen and oxygen isotopes of nitrate within marine ecosystems can provide a record of the sources of nitrogen supporting biological production and the major pathways and mechanisms moving nitrogen through different pools.Current challenge for successful use of nitrogen and oxygen isotopes of nitrate in resolving nitrogen cycle fluxes and processes requires an analytical advance,an accurate construction of nitrogen budget,and a further understanding of processes affecting nitrogen and oxygen isotopes in the upper ocean.The spatial and temporal variation in the isotopic composition of nitrate requires a sampling extension among global oceans,especially in China marginal seas with little data now.