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反应，需要了解物理、化学和生物系统目前如何运作，以及它们可能如何对预测的环境变化做出反应。海洋内部的氧气消耗/利用(OUR)和营养物质再生率(NRR)为推断阳光充足的表层水域的海洋生产力提供了一个有吸引力的自下而上的方法。氧的利用率通常使用“瞬时示踪剂”的分布来估计，这些化合物如氯氟烃(CFCs)和六氟化硫(SF6)是由人类活动引入大气和海洋的。基于示踪剂的估计受到若干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比率最接近(和最差)的地方。根据示踪技术对生物地球化学循环速率和表层海洋生产力的调查将与卫星或ARGO花车等其他测量系统的调查结合起来，并将提供对海洋生物地球化学循环的更好看法。关于该技术在哪里发挥作用的建议对于解释未来水文学巡航的结果将是重要的，并可指导今后的示踪剂测量战略。调查人员将包括本科生暑期学生参与研究，并参与当地学校的推广计划。调查人员将使用多模型方法解决基于示踪剂的OUR和NRR中的偏差和不确定性。分析现有示踪剂模型的输出，包括氧、磷酸盐、氯氟烃、SF6、理想年龄和渡越时间分布(TTD)，将揭示在哪些区域和时间内，瞬时示踪剂年龄(结合氧气场)对模型中已知的氧气消耗项给出了最好的估计。他们将使用国家大气研究中心的并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，这还可以研究示踪剂推断的NRRs的准确性，包括反硝化速率、硅酸盐产量、碳酸钙溶解以及溶解的有机营养物质的再生速率。最后，计划在不久的将来将多种生物地球化学示踪算法添加到当前的脱机状态，这将使研究人员能够同时查看复杂的生物地球化学以及瞬时示踪、理想和TTD年龄的全谱。最后，它们将解决在最近和即将到来的气候变异性和预测/全球海洋船舶水文调查计划(CLIVAR/GO-SHIP)重复水文调查(RH)部分中观察到的OUR/NRR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.