Anammox, denitrification and nitrogen fixation in the Black Sea

本提案的目标是了解黑海缺氧区与氮循环有关的化学和微生物分布的巨大变异性。这种大的时间变异性最好的解释是微生物介导的过程，如厌氧氨氧化和硝化作用的变化。以前的工作已经确定了一些细菌存在于整个趋化cline中，但它们的代谢，活动以及对氮的生物地球化学平衡的相对贡献仍然知之甚少。该项目将通过测试两个假设来解决不同类型和丰度的微生物群的存在和缺失，以及它们的代谢活动。第一个假设是，颗粒有机碳通量的季节变化导致厌氧氨氧化和反硝化的相对重要性发生变化。第二个假设是，N2和δ 15 N-N2浓度的变异性是由光合区固氮产生的颗粒有机氮垂直通量的变异性决定的。主要研究人员将通过在俄罗斯研究船上进行四次短途巡航（春季、秋季、冬季和夏季）到黑海深水站的时间序列观察来解决这些假设。在这些巡航期间，将进行全面的水物理、化学和微生物采样，并测量颗粒有机碳的下沉通量。这些新的地球化学数据将用于扩展研究人员以前的数据集，具体观察氮种类和同位素分布以及年循环通量的变化。这里提出的生物学工作的具体重点是不仅要记录微生物群落的变化，而且要确定特定微生物群的活跃生长和基因转录。这项研究的影响超出了黑海，因为研究结果将帮助我们了解低氧条件下氮循环的一些控制。预测由于人为强迫而导致的未来变化的能力要求我们了解氮循环的当前动态。缺氧和厌氧环境容易受到人为强迫的影响，不仅在封闭的盆地，而且在高生产力和经济重要性的地区，如俄勒冈和华盛顿海岸，发挥着越来越重要的作用。这些结果还将揭示在整个地球历史上一直很重要的亚氧和厌氧过程。

The goal of this proposal is to understand the large variability in the chemical and microbial distributions related to nitrogen cycling in the suboxic zone of the Black Sea. The large temporal variability is best explained by changes by microbially mediated processes such as ANAMMOX and nitrification. Previous work has identified some of the bacteria present across the chemocline, but their metabolisms, activities, and relative contributions to the biogeochemical balance of nitrogen are still very poorly understood. This project will address not only the presence and absence of different types and abundances of microbial groups, but also their metabolic activity by testing two hypotheses. The first hypothesis is that the seasonal variability in the flux of particulate organic carbon causes variability in the relative importance of ANAMMOX and denitrification. The second hypothesis is that variability in the concentrations of N2 and Delta 15 N-N2 is determined by variability in the vertical flux of particulate organic nitrogen produced by nitrogen fixation in the euphotic zone. The principal investigators will address these hypotheses by conducting a time series of observations that consist of four short cruises (spring, fall, winter and summer) on a Russian research vessel to deep water stations in the Black Sea. During these cruises comprehensive hydrophysical, chemical and microbiological sampling, and measurements of the sinking flux of particulate organic carbon will be conducted. This new geochemical data will be used to expand on the investigators previous data sets by looking specifically at the variability in nitrogen species and isotope distributions and fluxes over the annual cycle. The specific focus of the biological work proposed here is to document not only changes in the microbial community, but to identify active growth and gene transcripts of specific groups of microbes. The study has ramifications beyond the Black Sea as the results will help us understand some of the controls on nitrogen cycling under low oxygen conditions in general. The ability to predict future change as a result of anthropogenic forcing requires that we understand the current dynamics in the nitrogen cycle. Suboxic and anaerobic environments are susceptible to anthropogenic forcing, and play an increasingly important role not only in enclosed basins but in areas of high productivity and economic importance, such as the Oregon and Washington coast. These results will also shed light on suboxic and anaerobic processes that have been important throughout Earth's history.