Collaborative Research: Isotopic Constraints on the Nitrogen Dynamics of the Bering Sea

本项目将研究极地海洋（特别是白令海）的反硝化机制，即溶解营养物NO3的化学还原，主要是惰性N2气体。海洋中的反硝化作用，即生物过程所必需的营养N的损失，通常被认为只发生在溶解氧相对缺乏（[O2] 5-10mM）的条件下。尽管整个北极地区的氧浓度很少低于15uM，但相对于磷酸盐而言，北极海洋显示出显著的硝酸盐损耗。多年来，人们已经知道白令海特别显示出相当大的硝酸盐赤字，但这是在水柱中还是在沉积物中，或者甚至可能是从太平洋低纬度氧气最低区平流进来的，目前还不清楚。硝酸盐的同位素测量将用于评估沉积反硝化与水柱反硝化的相对作用，基于观察到的伴随这两个过程的不同同位素特征。利用最近发展的同位素分析方法，海洋硝酸盐的d18o也将作为示踪剂来补充d15n差异的解释，以研究海洋氮循环的这些方面。该研究的进一步研究方向是考虑现代极地太平洋作为冰川南大洋的类似物的命题，这是解释大气二氧化碳全新世变化的一个关键未知因素，从而扩大了我们对地质近期气候变化的理解。

ABSTRACTOCE-0136449OCE-0136584This project will consider the mechanisms of denitrification - the chemical reduction of dissolved nutrient NO3- largely to inert N2 gas- in the polar oceans and specifically the Bering Sea. Denitrification in the ocean, the loss of nutrient N essential for biological processes, is conventionally thought to take place only in conditions of relative dissolved oxygen deficiency ( [O2] 5-10mM). The northern Polar ocean shows significant nitrate depletion relative to phosphate despite the concentration of oxygen rarely falling below 15uM throughout much of the region. It has been known for many years that the Bering Sea in particular exhibits a sizeable nitrate deficit, but whether this arises in the water column or in the sediments, or perhaps is even advected in from low-latitude oxygen minimum zones in the Pacific remains unclear. Isotopic measurements of nitrate will be used to assess the relative role of sedimentary vs. water column denitrification based on observed distinct isotopic signatures accompanying these two processes. Using a recently developed isotopic analytical method, the d 18O of oceanic nitrate will also be developed as a tracer to complement the interpretation of d 15N differences to study these aspects of the oceanic nitrogen cycle. A further line of enquiry of the study is to consider the proposition that the modern polar Pacific ocean operates as an analogue of the glacial Southern Ocean, a key unknown in interpreting Holocene variations in atmospheric CO2 and thus broadening our understanding of geologically recent climate change.