Collaborative Research: Measurement of tritium, helium isotopes, and noble gases on GO-SHIP line P18

GO-SHIP项目旨在描述热、淡水、碳、氧、营养物质和其他化学示踪剂在全球范围内随时间变化的海洋分布特征，以期阐明和量化重要的物理和生物地球化学过程，并记录全球变化。作为这项国际努力的一部分，2016年，沿东太平洋和南大洋约110°W（从下加利福尼亚到南极洲的冰缘）的经向部分P18被占领。这笔资金将用于测量海洋示踪剂——氚、3He/4He同位素比率，以及全套惰性气体（He、Ne、Ar、Kr和Xe）——对2016年P18剖面收集的约500份水样进行测量。示踪剂样品将在WHOI同位素地球化学设施的专门提取系统和质谱仪上进行处理。不断变化的海洋气候系统给我们带来的挑战从未像现在这样重要。冰川和海冰融化加剧、海平面上升、海洋酸化和脱氧是必须预测的一些重要社会效应，如果可能的话，还可以利用全球海洋环流和生物地球化学模型进行定量预测。这样的模型需要对固有过程有更好的理解，因为它们必然是复杂的，而且是对现实的不完整的抽象，它们需要对校准、测试和（如果可能的话）验证进行观察。在许多其他观测数据集和理论的背景下，评估和记录这些示踪剂的分布及其演变，将为全球海洋-气候物理和生物地球化学模型提供有价值的约束，这些模型是理解和处理全球变化的关键。新的P18氚- 3he和惰性气体数据将通过CLIVAR和碳水文办公室（CCHDO）网站公开提供给任何感兴趣的各方。该项目的科学目标是：(1)记录2016年P18剖面上相对于1994年和2008年早期职业的氚和3He分布的演变，以阐明东太平洋通风和环流的十年尺度模式和可能的气候变化；(2)在东太平洋和南大洋进行第一次高质量的稀有气体测量，以表征海气交换效应和洋底旋流混合对太平洋溶解气体的影响，以及冰川融化对环极深水的贡献。在美国全球海洋碳和重复水文测量计划中，氚- 3he是二级（“非常理想”）数据集，该数据集与核心GO-SHIP计划分开资助，但在很大程度上利用并增加了测量和船舶时间。新的氚- 3he和稀有气体数据将在2016年GO-SHIP P18水文和示踪剂观测（例如CFCs， SF6, O2）， 1994年和2008年以前P18观测的氚- 3he数据以及其他GO-SHIP和GEOTRACES剖面的太平洋盆地尺度氚- 3he数据的背景下进行解释。新的示踪剂数据为东太平洋和南大洋的物理和生物地球化学过程提供了独特而有价值的信息：氚作为一种瞬态示踪剂具有独特的半球不对称性，可以用作热带南北水团来源的诊断示踪剂。氚氦定年法提供了一种独特而灵敏的浅层通风和环流的年至年代际时间尺度测量方法，与其他示踪剂（如氯氟烃和SF6）不同，它可以估计浅层水域的水团起源、年龄和变化。深海氦同位素为热液羽流的来源、扩散和稀释以及约束深水环流模式提供了重要信息。稀有气体是气-海交换、水团物源、冰-海相互作用、上升流和原位岩浆混合的敏感而明确的示踪剂。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The GO-SHIP program seeks to characterize the time-evolving global scale ocean distributions of heat, freshwater, carbon, oxygen, nutrients and other chemical tracers with a view to illuminating and quantifying important physical and biogeochemical processes and to document global change. As part of this international effort, the meridional section P18 was occupied in 2016 along approximately 110°W in the eastern Pacific and Southern Ocean (from Baja California to the ice edge off Antarctica). The grant will fund efforts to measure ocean tracers – tritium, 3He/4He isotope ratio, and the full suite of noble gases (He, Ne, Ar, Kr, and Xe) – on approximately 500 archived water samples collected on the 2016 P18 section. The tracer samples will be processed on specialized extraction systems and mass spectrometers at the WHOI Isotope Geochemistry Facility. Evolving ocean-climate systems present us with challenges that are never more important than now. Increased glacial and sea-ice melting, increasing sea level, ocean acidification, and deoxygenation are a few of the societally important effects that must be anticipated and if possible quantitatively predicted using global ocean circulation and biogeochemical models. Such models require a better understanding of the inherent processes, and because they are necessarily complex, yet incomplete abstractions of reality, they need observations for calibration, testing, and (if ever possible) verification. Evaluation and documentation of the distributions of these tracers and their evolution, within the context of many other observational data sets and theories, will provide valuable constraints on global ocean-climate physical and biogeochemical models that are key to understanding and dealing with global change. The new P18 tritium–3He and noble gas data will be made publicly available to any interested parties through the CLIVAR and Carbon Hydrographic Office (CCHDO) site. The project science objectives are to: (1) Document the evolving tritium and 3He distributions in 2016 on the P18 section relative to the earlier 1994 and 2008 occupations to illuminate decadal-scale patterns and possible climatic changes in ventilation and circulation in the eastern Pacific; (2) Make the first high quality noble gas measurements in the eastern Pacific and Southern Ocean to characterize air-sea exchange effects and diapycnal mixing on dissolved gases in the Pacific, and glacial melt contributions to the Circumpolar Deep Water. In the U.S. Global Ocean Carbon and Repeat Hydrography Program, tritium–3He is a Level 2 (“highly desirable”) data set that is funded separate from, but heavily leverages and adds to the measurements and ship time conducted by the core GO-SHIP program. The new tritium–3He and noble gas data will be interpreted in the context of the 2016 GO-SHIP P18 hydrographic and tracer observations (e.g., CFCs, SF6, O2), tritium–3He data from previous P18 occupations in 1994 and 2008, and Pacific basin-scale tritium–3He data from other GO-SHIP and GEOTRACES sections. The new tracer data offer unique and valuable information on physical and biogeochemical processes in the eastern Pacific and Southern Ocean: Tritium as a transient tracer has a unique hemispheric asymmetry that can be used as a diagnostic tracer of north vs south water mass provenance in the tropics. Tritium-helium dating provides a unique and sensitive measure of shallow ventilation and circulation on annual to decadal time-scales that is distinct from other tracers such as CFCs and SF6, giving estimates of water mass origins, ages, and modification in shallow waters. Helium Isotopes in the deep water provide important information regarding hydrothermal plume provenance, dispersion and dilution, and constraining deep-water circulation models. Noble gases are sensitive and unambiguous tracers of air-sea exchange, water mass provenance, ice-ocean interaction, upwelling, and in situ diapycnal mixing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.