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，以研究热带南太平洋东部（ESTP-10°S-20°S，80°W-110°W）的固氮作用，并确定其作为新氮源对该地区初级生产的贡献。 拟议的巡航路线涵盖了各种各样的初级生产力，从世界上一些生产力最高的海洋沃茨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，参加考察，以量化固氮作用对初级生产率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海洋上层溶解的生物O2过饱和度和17 O过量氧气来确定净群落生产和总光合生产（NCP和GPP）。 通过测量近地表沃茨的O2/Ar比值可以确定生物过程中的氧过饱和度，有效地消除了气泡注入等物理过程产生的过饱和度的影响。过量的17 O使得通过光合作用原位产生的地表水氧与来自大气的氧区别开来。 此外，还将获得上层水柱中的222 Rn剖面，并将其用于评估气-海气体交换率和温跃层中的涡流扩散率。 还计划建立一个在进行中测量近地表氡的系统，该系统应能确定气体交换的空间/时间变化，并有助于确定最近上升或下降的水团。 O2/Ar和三角洲17 O方法的结果，再加上氡不足的区域映射将产生一个很好的数据基础，估计碳出口内的ETSP.In更广泛的影响，研究可能会导致减少不确定性的气体交换率，可以提高生产力测量的精度。 该项目代表了洛杉矶地区两个学术机构之间的合作努力。 作为该项目的一部分，南加州大学的一名博士后和两名本科生将得到支持和培训。

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.