Evaluating the Accuracy of Biogeochemical Cycling Rates from Transient Tracers

要预测未来海洋对二氧化碳的吸收，从而预测海洋/陆地/大气耦合系统对气候强迫的响应，就需要了解物理、化学和生物系统目前如何运作，以及它们如何可能对预测的环境变化作出反应。海洋内部的氧气消耗/利用（OUR）和养分再生（NRR）率提供了一种有吸引力的自下而上的方法来推断阳光照射的表层水域的海洋生产力。氧利用率通常是用“瞬态示踪剂”的分布来估计的，即人类活动引入大气和海洋中的氯氟烃和六氟化硫等化合物的分布。基于示踪剂的估计受到几个因素的不确定性的影响，包括示踪剂的时间历史和海洋混合。华盛顿大学的研究人员计划使用海洋模型来检查这些不确定性的来源，并确定海洋中基于示踪剂的估计与实际速率最一致（和最不一致）的地方。基于示踪技术的生物地球化学循环速率和海洋表面生产力的研究将与其他测量系统（如卫星或Argo浮标）的研究结合起来，并将提供对海洋生物地球化学循环的改进看法。关于该技术在何处起作用的建议对于解释未来水文巡航的结果非常重要，并且可以指导未来示踪剂测量的策略。调查人员将在研究中包括本科生暑期学生，并参与当地学校的外展项目。研究人员将使用多模型方法解决基于示踪剂的our和NRRs中的偏差和不确定性。对现有示踪剂模型输出的分析，包括氧、磷酸盐、CFCs、SF6、理想年龄和传输时间分布（TTDs），将揭示在哪些区域和时间内，瞬态示踪剂年龄（结合氧场）对模型中已知的耗氧量项给出了最好的估计。他们将使用国家大气研究中心的平行海洋计划模型输出（仅海洋配置）来扩展这项工作，该模型包含更多种类的生物地球化学参数和更复杂的生物地球化学（尽管没有SF6， TTDs或理想年龄旋转到稳定状态）。除了我们的数据外，还可以对示踪剂推断的nrr的准确性进行调查，包括反硝化速率、硅酸盐生成速率、碳酸钙溶解以及溶解有机营养物的再生速率。最后，计划在不久的将来将多种生物地球化学示踪剂算法添加到当前的离线中，将使研究人员能够同时查看复杂的生物地球化学和瞬态示踪剂、理想年龄和TTD年龄的全谱。最后，他们将讨论在最近和即将到来的气候变率和预测/全球海洋船舶水文调查计划（CLIVAR/GO-SHIP）重复水文（RH）部分观测到的our /NRRs的明显变化的稳健性。

The ability to predict future oceanic uptake of carbon dioxide and, consequently, the response of the coupled ocean/land/atmosphere system to climate forcing, requires an understanding of both how the physical, chemical, and biological systems presently function and how they are likely to respond to predicted environmental changes. Oxygen consumption/utilization (OUR) and nutrient regeneration (NRR) rates in the ocean interior provide an attractive bottom-up approach to infer marine productivity in the sunlit surface waters. Oxygen utilization rates are often estimated using the distributions of "transient tracers,' compounds such as chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) that are introduced in to the atmosphere and oceans by human activity. Tracer-based estimates are subject to uncertainties based on several factors including the time history of the tracers and ocean mixing. Investigators at the University of Washington plan to use ocean models to examine the sources of these uncertainties and determine where in the oceans the tracer-based estimates agree best (and worst) with the actual rates. The investigation of biogeochemical cycling rates and surface ocean productivity based on tracer techniques will be put into context with those from other measurement systems such as satellite or Argo floats and will provide an improved view of biogeochemical cycling in the ocean. Recommendations on where the technique works will be important for the interpretation of results from future hydrographic cruises and can guide strategies for future tracer measurements. The investigators will include undergraduate summer students in the research, and participate in outreach programs in local schools.The investigators will address the biases and uncertainties in the tracer-based OURs and NRRs using a multi-model approach. Analysis of existing tracer model output, including oxygen, phosphate, CFCs, SF6, ideal ages and transit time distributions (TTDs), will reveal in which regions and during which times transient tracer ages (combined with oxygen fields) give the best estimation of the known oxygen consumption terms in the model. They will expand this work using the National Center for Atmospheric Research's Parallel Ocean Program model output (ocean-only configuration) which contains a much larger variety of biogeochemical parameters and more complex biogeochemistry (though no SF6, TTDs or ideal age spun up to steady state). In addition to OURs, this allows investigation of the accuracy of tracer-inferred NRRs, including denitrification rates, silicate production rates, and calcium carbonate dissolution, as well as regeneration rates of dissolved organic nutrients. Finally, a planned, near-future addition of multi-biogeochemical tracer algorithms to the current offline will enable the investigators to look at complex biogeochemistry and the full spectrum of transient tracer, ideal, and TTD ages simultaneously. Finally they will address the robustness of apparent changes in OURs/NRRs observed during recent and upcoming Climate Variability and Prediction/Global Ocean Ship-based Hydrographic Investigations Program (CLIVAR/GO-SHIP) Repeat Hydrography (RH) sections.