Using Ocean Tritium/Helium-3 Observations to Quantify Thermocline Circulation and Biogeochemistry

在这项研究中，来自伍兹霍尔海洋研究所的研究人员将对海洋氚/氦-3观测的大量数据集进行首次系统和连贯的全球规模分析，并将研究结果纳入全球地球系统模型。 20世纪50年代末和60年代初的核武器试验向大气中释放了大约400公斤的氚，这是氢的放射性同位素。 大部分氚通过降水进入北方表层海洋。氚和氦-3（氚发生放射性衰变时产生）随后在海洋中的移动是海洋环流和混合的有力示踪剂。 在过去的四十年里，对全世界海洋沃茨中的氚/氦-3比率进行了实地测量，仅在北大西洋就收集了20 000多个样本。这项研究的结果将使人们更好地了解海洋中的氧气和营养物动态，并为社区地球系统模型（CESM）海洋模型增加新的功能，该模型广泛用于海洋物理，海洋地球化学和生态研究以及气候变化研究。研究人员还将把研究结果纳入研究生课程。释放到海洋中的氚是大洋俯冲、环流和温跃层及新形成的深、中层沃茨混合的有力示踪剂。氚还作为营养素的化学和生物惰性类似物，以及一种独特的示踪剂，可以跟踪和量化营养素上涌途径和生物新生产。这项研究将提供北大西洋和北太平洋海洋氚/氦-3观测的综合结果，将四十多年的实地观测汇集成一个单一的公开数据集。海洋学数据分析技术与诊断和逆向建模相结合，然后将用于估计物理和地球化学速率。先进的三维海洋环流模式的氚/氦-3模拟将用于解决诊断建模中使用的区域/时间数据缺口、物理传输机制和地球化学假设等问题。这项研究的总体结果将是海洋氚的时空演变特征，更好地了解氧的利用率，并结合表面氚数据与地下氚：营养分布。

In this study, researchers from the Woods Hole Oceanographic Institution will conduct the first systematic and coherent global-scale analysis of a considerable dataset of ocean tritium/helium-3 observations, and integrate findings into a global Earth System Model. Nuclear weapons tests in the late 1950s and early 1960s released into the atmosphere approximately 400 kilograms of tritium, a radioactive isotope of hydrogen. A large fraction of the tritium entered the Northern Hemisphere surface ocean via precipitation. The subsequent movement of tritium and helium-3 (produced when tritium undergoes radioactive decay) in the oceans has served as a powerful tracer of ocean circulation and mixing. For the past four decades, field measurements of the tritium/helium-3 ratio in worldwide oceanic waters have been collected, amassing more than 20,000 samples in the North Atlantic alone. Results from this study will provide a better understanding of oxygen and nutrient dynamics in the oceans, and will add new capabilities to the Community Earth System Model (CESM) ocean model, which is widely used for ocean physical, biogeochemical, and ecological research as well as climate change research. The researchers will also incorporate the results of the study into a graduate-level course. Tritium released into the oceans has been a powerful tracer of ocean subduction, circulation, and mixing in the thermocline and newly formed deep and intermediate waters. Tritium also acts as a chemically and biologically inert analogue for nutrients and a unique tracer allowing the tracking and quantification of nutrient upwelling pathways and biological new production. This study will provide a synthesis of ocean tritium/helium-3 observations for the North Atlantic and North Pacific, bringing together more than four decades of field observations into a single, publicly available dataset. Oceanographic data analysis techniques combined with diagnostic and inverse modeling then will be used to estimate physical and biogeochemical rates. Tritium/helium-3 simulations from an advanced 3-D ocean circulation model will be used to resolve issues involving regional/temporal data gaps, physical transport mechanisms, and biogeochemical assumptions used in the diagnostic modeling. Overall results of the study will be a characterization of the spatial and temporal evolution of ocean tritium, a better understanding of oxygen utilization rates, and combined surface tritium data with subsurface tritium:nutrient distributions.