Assessing Coastal Benthic Denitrification using High Precision Water Column N2/Ar

ABSTRACTProposal没有。[cn]据认为，大陆边缘的底栖生物反硝化作用超过水柱反硝化作用，但其幅度不太确定，部分原因是在相对较少的地点进行的困难的短期速率测量范围很大。对底栖生物反硝化作用的改进估计将促进我们对海洋氮动态和海洋氮收支状态的基本理解。在该提案中，来自马萨诸塞大学达特茅斯分校的PI将通过大大改进的N2/Ar测定方法，通过测量在大气N2大背景下积累在上覆水柱中的生物源N2，对沿海底栖生物反硝化进行地球化学评估。这些测量的一个主要优点是由水质量停留时间和与沉积物的接触面积决定的大空间/时间尺度的整合。为了实现这一目标，他将利用实验室同位素比质谱仪（IRMS）和海上四极杆质谱仪（QMS）仪器开发高精度和高通量的分析能力。在实验室中，通过IRMS和QMS的耦合运行，开发并优化了溶解气体萃取系统。样本收集和处理方案将通过码头取样进行季节性周期测试，并通过分析长岛湾每月水质评估调查收集的样本进行测试。DG-QMS系统的海上试验随后将在两次短途巡航中进行，届时将有大量预期的生物成因N2/Ar异常。用于质量控制测定化学计量关系的辅助测量包括O2/Ar、15N-N2、18O-O2、36Ar、DIC、13C-DIC和营养物浓度。此外，通过罗德岛大学（URI）的分包商，部署了一种新的剖面气体张力装置，将测试该技术在脱硝研究中的潜力，并结合高精度气体比分析。该提案的更广泛影响包括发展解决最近出现的关于海洋N循环的主要问题的能力，这是一个主要的生物地球化学循环，反过来又影响全球碳循环。反硝化在改善由人为N输入引起的沿海富营养化方面也具有重要作用，本项目的LIS部分在这方面具有直接相关性。拟议的工作将为未来的海洋反硝化研究创造重要的技术，并利用高精度水柱N2/Ar对底栖生物反硝化进行首次地球化学评估。拟议的研究将扩大新马萨诸塞大学校际研究生院的范围，并将通过URI的合作促进思想和成果的交流。在此过程中，本科生和研究生将通过参与本项目，第一次接触到海洋生物地球化学和海洋学研究。该项目将特别支持硕士或博士研究生检查LIS时间序列样本。

ABSTRACTProposal No.: OCE-0623199Benthic denitrification on continental margins is thought to exceed water column denitrification, but its magnitude is less certain due in part to the large range in difficult, short-term rate measurements made at relatively few locations. Improved estimates of benthic denitrification will advance our fundamental understanding of marine N dynamics and the state of the oceanic N budget. In this proposal, a PI from University of Massachusetts - Dartmouth, will conduct a geochemical assessment of coastal benthic denitrification by measuring the biogenic N2 that accumulates in the overlying water column against the large background of atmospheric N2 through greatly improved N2/Ar determination. A major advantage of these measurements will be the large space/time scales of integration as determined by water mass residence time and contact area with the sediments.To accomplish this goal, he will develop very high precision and high throughput analytical capability using lab-based isotope ratio mass spectrometer (IRMS) and sea-going quadrupole mass spectrometer (QMS) instruments. In the laboratory, a dissolved gas extraction system will be developed and optimized through coupled operation of the IRMS and QMS. Sample collection and handling protocols will be tested by dockside sampling through a seasonal cycle as well by analysis of samples collected on monthly water-quality assessment surveys of Long Island Sound (LIS). Sea trials of the DG-QMS system will then be carried out on two short cruises to LIS with its large expected biogenic N2/Ar anomalies. Ancillary measurements for quality control determination of stoichiometric relationships include O2/Ar, 15N-N2, 18O-O2, 36Ar, DIC, 13C-DIC, and nutrient concentrations. In addition, via a subcontractor at University of Rhode Island (URI), deployment of a new profiling gas tension device will test the potential of this technology for denitrification studies in conjunction with high precision gas ratio analysis.The broader impacts of this proposal include developing capability for addressing major questions that have recently arisen regarding the ocean's N cycle which as a major biogeochemical cycle in turn impacts global carbon cycling. Denitrification also has an important role in ameliorating coastal eutrophication stimulated by anthropogenic N input, and the LIS component of this project has direct relevance in this regard. The proposed work will create technology important for future studies of marine denitrification as well as conduct the first geochemical assessment of benthic denitrification using high precision water column N2/Ar. The proposed research will expand the scope of the new University of Massachusetts Intercampus Graduate School and will foster the exchange of ideas and results through collaborations at URI. During the course of this work, undergraduate and graduate students will be exposed to marine biogeochemical and oceanographic research for the first time through their involvement in this project. The project will specifically support a M.S. or Ph.D. student to examine the LIS time-series samples.