Collaborative Research: Control of Denitrification and Anammox in the Oxygen Deficient Waters of the Eastern Tropical North and South Pacific

最基本的问题仍然是氧气最小区(OMZ)中的氮(N)循环，以及反硝化和厌氨氧化对固定氮损失的相对贡献。华盛顿大学和普林斯顿大学的科学家最近的工作表明，在阿拉伯海的OMZ中发生了厌氨氧化和反硝化作用，并表明与东热带南太平洋(ESTP)的OMZ的报告相反，反硝化作用主导着固定氮的去除。观察到的差异归因于提供给OMZ水域的有机碳的性质和时间。在这个项目中，科学家们建议通过记录以下情况来解释在OMZ中观察到的有限的反硝化作用：反硝化作用与来自地表水的有机碳的通量有关，而Anammox不直接对有机C输入做出反应，而是依赖于有机物分解过程中释放的可溶副产物(如铵和亚硝酸盐)的通量。将开展一项实地方案，涉及两个独立的巡航，一个前往东热带北太平洋(ETNP)，一个前往东热带北太平洋(ETNP)。之所以选择这些地点，是因为ESTP是三个主要OMZ中研究最多的，而ETNP是体积最大的OMZ，在数量上可能是联合脱氮最重要的。实现其目标的实验计划包括：(1)使用广泛的空间覆盖作为高分辨率时间覆盖的替代，以获得许多反硝化和厌氧氨氧化速率的测量；(2)使用操纵实验来研究反硝化和厌氧氨氧化速率对特定扰动的响应，例如有机物添加和瞬时氧气扰动；(3)在培养实验中使用新的示踪剂测量来区分反硝化作用、异化硝酸盐还原为氨氮和厌氧氨氧化；(4)使用DNA/RNA微阵列来研究转化速率和反硝化菌组合之间的关系，以确定颗粒在反硝化速率刺激中的作用；(5)使用高灵敏度的氧探头来确定氧的分布，并在示踪剂孵育过程中跟踪低水平的氧动力学。在更广泛的影响方面，华盛顿大学计划在R/V Thompson号上贡献时间，以便本科生可以参加邮轮，了解开展海洋研究所涉及的方法和技术，特别是与本研究相关的方法和技术。作为该项目的一部分，华盛顿大学的一名研究生和普林斯顿大学的一名博士后、一名研究生和一名本科生将得到支持和培训。

Fundamental question remain on how nitrogen (N) cycles in oxygen minimum zones (OMZs) and on the relative contribution of denitrification and anammox to the loss of fixed N. Recent work by scientists at the University of Washington and Princeton University showed the occurrence of anammox and denitrification in the OMZ of the Arabian Sea and indicated that denitrification dominated the fixed N removal in contrast to reports for the OMZ in the Eastern Tropical South Pacific (ESTP). The observed difference was attributed to the nature and timing of organic carbon supplied to the OMZ waters. In this project, the scientists propose to explain the limited observations of denitrifications in the OMZs by documenting that denitrification is linked to the flux of organic carbon from surface waters whereas anammox does not respond directly to organic C inputs but depends on the flux of soluble byproducts such as ammonium and nitrite released during the breakdown of organic matter. A field program involving two separate cruises, one to the ETSP and one to the Eastern Tropical North Pacific (ETNP) will be carried. These sites were selected because the ESTP is the most studied of the three major OMZs whereas the ETNP is the largest OMZ by volume and may be quantitatively the most important in terms of combined nitrogen removal. The experimental plan to attain their goals include the following: (1) use extensive spatial coverage as a substitute for high resolution temporal coverage to obtain many measurements of denitrification and anammox rates; (2) use manipulation experiments to investigate the response of denitrification and anammox rates to specific perturbations such as organic matter additions and transient oxygen perturbation; (3) use new tracer measurements to distinguish denitrification, dissimilatory nitrate reduction to ammonium and anammox in incubation experiments; (4) use DNA/RNA microarrays to investigate relationships between transformation rates and the denitrifier assemblage to resolve the role of particles in stimulation of denitrification rates; and (5) use high sensitivity oxygen probes to define the oxygen distribution and to follow oxygen dynamics at low levels in tracer incubation. In terms of the broader impacts, the University of Washington plans to contribute time on the R/V Thompson so that undergraduate students can participate in a cruise and learn about the methods and techniques involved in carrying out oceanographic research, especially those related to this study. One graduate student from the University of Washington and one postdoc, one graduate student and one undergraduate student from Princeton University would be supported and trained as part of this project.