风尘刺激下的固氮作用在西北太平洋亚热带环流区沉积物捕获器中的记录

北太平洋亚热带环流区是典型的寡营养海域，该区域表层水体中硝酸盐长期处于耗尽状态，生物生产力极低。尽管如此，由于该海域生态系统是地球上最大的生态系统之一，该海域生态系统生产力的微小变化都会对全球碳循环都有一个重要的影响。生物固氮作用引入的结合态氮是该海域的一个重要氮源，对输出生产力有着重要的贡献，大气沉降输入的Fe是限制该海域固氮作用的主要化学因子，因此大气沉降通量的变化对该区域的固氮作用有着重要的影响。本项目拟通过沉积物捕获器中沉降颗粒有机氮含量及其同位素组成分析，结合水体硝酸盐氮同位素组成，利用氮及其同位素质量平衡模型估算：（1）上层海洋生物固氮作用强度及其对输出生产力贡献的季节和年际变化；（2）固氮作用对在深层沉降颗粒有机碳的贡献。在此基础上结合卫星遥感手段观测该区域大气沉降通量的时间序列变化，研究大气沉降输入的铁对生物固氮的刺激作用，并探讨该海域大气沉降通量的变化对生物碳泵的影响。

The North Pacific subtropical gyre (NPSG) is considered to be the marine analogues of terrestrial desert because of chronic nutrient depletion. Despite of low rates of ecosystem production, it contributes significantly to the global productivity as NPSG is one of the largest ecosystems in the world, and even a small change of marine productivity in this area will influence distinctly on global carbon cycle. N2 fixation as the most important nitrogen supplier plays a key role to promote the primary production, and has an important contribution to the export production in this area. On the other hand, the N2 fixation is basically controlled by aeolian-supplied Fe in this area. In this project, the seasonal and annual change of nitrogen export and nitrogen isotopic composition in the NPSG will be analyzed using the particle samples collected by time-series sediment traps, and nitrogen isotopic composition of water column nitrate will also be measured. The intensity of N2 fixation and its contribution to the export production and to the settling particle organic carbon will be calculated with the method of the nitrogen isotope balance. The change of aeolian dust deposition recorded by real-time satellite observation will be utilized to study the relationship between the variations of N2 fixation and aeolian-supplied Fe flux, and their impact on the biological carbon export in the studied area.