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

建议编号：OCE-0623199大陆边缘的底栖生物反硝化作用被认为超过了水柱反硝化作用，但其大小不太确定，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的范围很大。改进的底栖反硝化估算将促进我们对海洋氮素动态和海洋氮素收支状况的基本理解。在这项提案中，马萨诸塞大学达特茅斯分校的一名PI将通过大大改进的N_2/Ar测定，在大气N_2的大背景下测量积累在上覆水柱中的生物N_2，从而对沿海底栖生物反硝化作用进行地球化学评估。这些测量的一个主要优势是由水质量停留时间和与沉积物的接触面积确定的大空间/时间尺度的积分。为了实现这一目标，他将利用实验室的同位素比质谱仪(IRMS)和海上四极质谱计(QMS)仪器开发非常高精度和高通量的分析能力。在实验室中，将通过IRMS和QMS的耦合运行来开发和优化溶解气体提取系统。样本收集和处理方案将通过季节性周期的码头采样以及对长岛海湾每月水质评估调查所收集的样本进行分析来测试。DG-QMS系统的海上试验随后将在前往LIS的两次短途航行中进行，LIS预计会出现较大的生物成因氮气/Ar异常。用于确定化学计量关系的质量控制的辅助测量包括O2/Ar、15N-N2、18O-O2、36Ar、DIC、13C-DIC和营养浓度。此外，通过罗德岛大学(URI)的一家分包商，部署一种新的剖面气体张力装置将测试这项技术在反硝化研究中的潜力，并结合高精度的气体比率分析。这项提议的更广泛影响包括发展解决最近出现的有关海洋N循环的主要问题的能力，海洋N循环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。反硝化作用在改善人为N输入刺激的沿海富营养化方面也有重要作用，该项目的LIS部分在这方面具有直接相关性。拟议的工作将创造对未来海洋反硝化研究非常重要的技术，并首次使用高精度水柱N_2/Ar进行底栖生物反硝化的地球化学评估。拟议的研究将扩大新的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。在这项工作的过程中，本科生和研究生将通过参与这一项目第一次接触到海洋生物地球化学和海洋学研究。该项目将专门支持一名硕士或博士生研究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.