西北太平洋溶解有机氮固氮来源及矿化作用的同位素示踪

溶解有机氮（DON）在调节热带、亚热带上层海洋的生物地球化学循环和生态系统结构与功能中扮演着重要角色，由于受到传统观点限制、分析测试手段局限等原因，迄今对海洋DON循环的理解仍十分薄弱。固氮作用是热带、亚热带开阔大洋最重要的新氮输入来源之一，因此，探明DON的固氮来源及矿化作用，是理解海洋DON源汇过程的关键。本项目将以西北太平洋这一理想研究区域为对象，以DON的同位素组成为切入点，综合天然同位素测定、标记同位素示踪实验、分子生物学分析、箱式模型等手段，揭示西北太平洋上层水体DON含量及同位素组成的时空变化，探明DON与固氮作用之间的内在关联，检验DON矿化过程及相关同位素分馏导致次表层硝酸盐δ15N极小值的假说，同时，引入全新的同位素参数（Δδ15N(DON-NO3)），揭示DON的源汇格局。倘若能获得资助，可望在海洋DON循环的同位素示踪这一前沿领域取得创新性成果。

Dissolved organic nitrogen (DON) plays an important role in regulating biogeochemical cycles and the structure/function of the upper ocean ecosystem in tropics and subtropics. However, our understanding of marine DON cycle is by far insufficient due to traditional views and analytical difficulties. N2 fixation is one of the most important new nitrogen sources for the tropical/subtropical open ocean. Undoubtedly, examining the contribution of N2 fixation to DON and subsequent decomposition will provide invaluable insights into understanding the key pathways of source and sink of DON in the ocean. In this study, multiple tools including natural isotopic composition (δ15N), isotope tracer assay, molecular biology analysis, box model, etc., will be applied to investigate DON cycle in the northwestern Pacific Ocean. From an isotopic perspective, we aim to: (1) obtain the spatio-temporal distribution patterns of DON concentration and its δ15N; (2) reveal the link between DON and N2 fixation; (3) test the hypothesis that DON remineralization and relevant isotopic fractionation plays a major role in the formation of the subsurface nitrate δ15N minimum; and (4) introduce a new isotopic parameter (Δδ15N(DON-NO3)) as an indicator of DON source or sink for a given oceanic region. This study in the cutting-edge field will help better understand some key aspects of DON cycle in the ocean.