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

最近，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)固氮的发生，并确定其作为该区域初级生产的新氮源的贡献。拟议的邮轮航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海域到生产力最低的海域。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，参加这些邮轮，以量化固氮对初级生产力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氧过饱和度和上层海洋中溶解的氧的17O过剩来确定净群落生产和总光合作用生产(NCP和GPP)。生物过程的氧过饱和度可以通过测量近地表水体的O2/Ar比来确定，这有效地消除了气泡注入和其他物理过程产生的过饱和的影响。过量的17O允许将原位光合作用产生的地表水氧气与大气中的氧气区分开来。此外，还将获得上层水柱中的222Rn剖面，并用于评估海气交换速率和跨温跃层的涡旋扩散率。还计划建立一个测量正在进行中的近地表氡的系统，该系统应确定气体交换的空间/时间变异性，并帮助查明最近涌升或下降的水团。对于O2/Ar和Delta 17O方法的结果，再加上氡缺乏的区域制图，将为ETSP内的碳出口估计提供一个很好的数据基础。从更广泛的影响来看，这项研究可能会减少气体交换率的不确定性，从而提高生产力测量的精度。这个项目代表了洛杉矶地区两个学术机构之间的合作努力。南加州大学的一名博士后和两名本科生将作为该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.