The Marine Dissolved N2/Ar Ratio, A Tracer for Deep Ocean Denitrification?

海洋溶解的 N2/Ar 比率，深海反硝化的示踪剂？

• 批准号: 1029299
• 负责人: Steven Emerson
• 金额: $ 50.35万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-15 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1029299&HistoricalAwards=false
• 关键词: Marine; Dissolved; N2; Ar; Ratio

The role of nitrate in the ocean carbon cycle and its relatively short residence time make it crucial to understand the marine nitrogen cycle; however, there is currently insufficient experimental evidence to accurately determine present day fluxes. Denitrification and nitrogen fixation are the main sink and source for dissolved inorganic nitrogen in the sea. In this study a research team at the University of Washington will collaborate with colleagues at the University of Victoria to study changes in the N2/Ar ratio in seawater caused by denitrification. Previous research has demonstrated the utility of this tracer in the oxygen minimum zones of the Pacific and Indian Ocean, but they will investigate observed changes in the "background" distribution of the ratio. The investigators already have unpublished data that indicate the N2/Ar ratio increases by about 0.5 % from the Atlantic to Pacific Oceans in waters below 1000 meters. If this increase is assumed to be caused by denitrification in deep ocean sediments it amounts to roughly 80 Tg/yr of denitrification. This is a significant portion of estimated global denitrification (between 200 and 400 Tg/yr) and within the range of the largely untested predictions of deep-ocean sediment denitrification using global sediment diagenesis models. Presently it is not possible to unequivocally attribute the observed deep water column N2/Ar increase to denitrification because it could also be caused by deep-water formation processes in the Antarctic. The investigators will separate the fraction of the N2/Ar ratio increase due to the physical processes of atmosphere or ice-water interaction from that due to denitrification by measuring other noble gas ratios (primarily Ne/Ar and Kr/Ar) that change only in response to ocean surface cooling and bubble processes. They will measure deep water-column profiles of N2/Ar, Ne/Ar and Kr/Ar in strategically-located sites where there are ships of opportunity: the Labrador Sea, the North Atlantic at the Bermuda time-series site, the Drake Passage, the Indian Ocean south of Madagascar, the subtropical North Pacific at the Hawaii Ocean time-series site, and the subarctic North Pacific at Station P. Preliminary measurements of all of the gas ratios have been made, and extensive testing has been done to identify sources of contamination in the sampling methods. This proposal involves a two-laboratory collaboration to make it possible to sample a large number of ocean sites, minimize atmospheric contamination by rapid sample analysis, and create maximum accuracy through laboratory intercalibration. Broader Impacts: This project will promote international ocean science collaboration between the U.S.and Canada. It will support the research of an assistant professor to apply analytical methods that she has helped develop to an important problem in oceanography. A PhD candidate at the University of Washington will be trained in the area of chemical oceanography using analytical methods of gas ratio and isotope ratio mass spectrometry.

硝酸盐在海洋碳循环中的作用及其相对较短的停留时间使其对了解海洋氮循环至关重要;然而，目前没有足够的实验证据来准确确定当今的通量。 反硝化作用和固氮作用是海水中溶解无机氮的主要汇和源。 在这项研究中，华盛顿大学的一个研究小组将与维多利亚大学的同事合作，研究反硝化作用引起的海水中N2/Ar比率的变化。 以前的研究已经证明了这种示踪剂在太平洋和印度洋氧气最低区的实用性，但他们将调查观察到的比例“背景”分布的变化。 研究人员已经有了未公布的数据，表明在1000米以下的沃茨，从大西洋到太平洋，N 2/Ar比率增加了约0. 5%。 如果假设这种增加是由深海沉积物中的脱氮作用引起的，那么它相当于大约80 Tg/年的脱氮作用。 这是估计的全球脱氮（200和400 Tg/年之间）的一个重要部分，并在深海沉积物脱氮的基本上未经测试的预测范围内，使用全球沉积物成岩模型。 目前还不可能明确地将观测到的深水水柱N2/Ar增加归因于脱氮作用，因为这也可能是南极深水形成过程造成的。 研究人员将通过测量其他惰性气体比率（主要是Ne/Ar和Kr/Ar），将由于大气或冰水相互作用的物理过程而导致的N2/Ar比率增加的部分与由于反硝化作用而导致的N2/Ar比率增加的部分分开，这些比率仅响应于海洋表面冷却和气泡过程。 他们将在有机会的战略地点测量N2/Ar、Ne/Ar和Kr/Ar的深水柱剖面：拉布拉多海、百慕大时间序列站点的北大西洋、德雷克海峡、马达加斯加以南的印度洋、夏威夷海洋时间序列站点的亚热带北太平洋、已经对所有气体比率进行了初步测量，并进行了广泛的测试，以确定采样方法中的污染源。 这一提议涉及两个实验室的合作，以便能够对大量海洋地点进行取样，通过快速样品分析尽量减少大气污染，并通过实验室相互校准实现最大的准确性。 更广泛的影响：该项目将促进美国和加拿大之间的国际海洋科学合作。 它将支持一名助理教授的研究，将她帮助开发的分析方法应用于海洋学的一个重要问题。 华盛顿大学的一名博士候选人将接受使用气体比率和同位素比率质谱分析法的化学海洋学领域的培训。