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

这个项目将研究极地海洋，特别是白令海中的反硝化作用的机制--将溶解的营养物质NO3化学还原为惰性氮气。海洋中的反硝化作用是生物过程所必需的营养氮的损失，传统上认为只有在相对溶解氧不足([O2]5-10 mm)的条件下才会发生。与磷酸盐相比，北极海洋显示出显著的硝酸盐消耗，尽管该地区大部分地区的氧气浓度很少降至15微米以下。多年来，人们已经知道，白令海尤其表现出相当大的硝酸盐亏缺，但这是出现在水柱还是沉积物中，或者甚至是从太平洋低纬最低含氧区平流进来的，目前尚不清楚。硝酸盐的同位素测量将用于根据观测到的伴随这两个过程的不同同位素特征来评估沉积反硝化和水柱反硝化的相对作用。利用最近开发的同位素分析方法，海洋硝酸盐的d18O也将被开发为示踪剂，以补充对d15N差异的解释，以研究海洋氮循环的这些方面。这项研究的另一条线索是考虑这样一个命题，即现代极地太平洋作为冰川作用的南大洋的类似物，在解释大气二氧化碳的全新世变化方面是一个关键的未知因素，从而拓宽了我们对地质上最近的气候变化的理解。

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.