Collaborative Research: Applying O2/Ar, DELTA17O and 222Rn methodologies to constrain organic carbon productivity in the upper ocean of the ETSP

最近，美国国家科学基金会资助了一项实地活动，研究南太平洋热带东部（ESTP-10°S-20°S, 80°W-110°W）固氮的发生情况，并确定其作为新氮来源对该地区初级生产的贡献。拟议的巡航轨道涵盖了初级生产力的广泛范围，从世界上一些生产力最高的到生产力最低的海洋水域。南加州大学的两名科学家将与加州大学洛杉矶分校的一名研究人员合作，参加邮轮活动，量化固氮对初级和出口生产率的贡献。为了实现他们的目标，研究人员将通过测量生物O2过饱和和上层海洋中溶解的氧过量来确定净群落产量和总光合产量（NCP和GPP）。生物过程产生的氧过饱和度可以通过测量近地表水的O2/Ar比值来确定，这有效地消除了气泡注入和其他物理过程产生的过饱和度的影响。过量的17O使得由光合作用产生的地表水氧气与来自大气的氧气区别开来。此外，还将获得上层水柱的222Rn剖面，并用于评估跨温跃层的海气交换率和涡动扩散率。还计划在进行中建立一个测量近地表氡的系统，以确定气体交换的空间/时间变化，并帮助确定最近上涌或下涌的水团。O2/Ar和δ 17O方法的结果，加上氡缺乏的面积测绘，将为估计ETSP内的碳输出提供一个极好的数据库。就更广泛的影响而言，该研究可能会降低气体交换率的不确定性，从而提高生产率测量的精度。该项目代表了洛杉矶地区两所学术机构之间的合作努力。来自南加州大学的一名博士后和两名本科生将作为项目的一部分得到支持和培训。

Recently the National Science Foundation funded a field campaign to study the occurrence of nitrogen fixation in the eastern tropical South Pacific (ESTP-10°S-20°S, 80°W-110°W) and determine its contribution as a source of new nitrogen to primary production in the region. The proposed cruise tracks cover a wide range in primary productivity, from some of the most productive to least productive marine waters in the world. Two scientists from the University of Southern California in collaboration with a researcher from the University of California, Los Angeles will participate in the cruises to quantify the contribution of nitrogen fixation to primary and export production rates. To attain their goal, the researchers would determine Net Community Production and Gross Photosynthetic Production (NCP and GPP) by measuring biological O2 supersaturation and 17O excess of oxygen dissolved in the upper ocean. Oxygen supersaturation from biological processes can be determined from measuring O2/Ar ratios of near surface waters, which effectively removes the effect of supersaturation produced by bubble injection and other physical processes. The 17O excess permits surface water oxygen that has been produced by photosynthesis in situ to be distinguished from oxygen from the atmosphere. In addition, 222Rn profiles in the upper water column would also be obtained and used to assess the rate of air-sea gas exchange and eddy diffusivity across the thermocline. A system to measure near-surface radon while underway is also planned and should ascertain spatial/temporal variability in gas exchange and help identify recently upwelled or downwelled water masses. Results for the O2/Ar and delta 17O methodologies, coupled with areal mapping of radon deficiencies will yield an excellent data base for estimation of carbon export within the ETSP.In terms of broader impacts, the research may lead to reduced uncertainties in the gas exchange rates which could improve the precision of productivity measurements. This project represents a collaborative effort between two academic institutions in the Los Angeles area. One postdoc and two undergraduate students from the University of Southern California will be supported and trained as part of the project.