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

Go-Ship计划寻求表征全球尺度海洋中热量、淡水、碳、氧、营养物质和其他化学示踪剂的时间演变分布，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。作为这一国际努力的一部分，2016年在东太平洋和南大洋(从下加利福尼亚州到南极洲冰缘)的西经约110°处占据了经向段P18。这笔赠款将用于测量海洋示踪剂--氚、3He/4He同位素比值和全套惰性气体(He、Ne、Ar、Kr和Xe)--在2016年P18段收集的大约500个存档水样上。示踪剂样品将在世界卫生组织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。不断演变的海洋气候系统给我们带来了前所未有的挑战。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见的几种社会重要影响，如果可能的话，还必须使用全球海洋环流和生物地球化学模型进行定量预测。这样的模型需要更好地理解内在过程，而且因为它们必然是对现实的复杂而不完整的抽象，它们需要用于校准、测试和(如果可能的话)验证的观察。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，将对全球海洋气候物理和生物地球化学模型提供宝贵的制约，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)网站向任何感兴趣的各方公开。项目的科学目标是：(1)记录2016年P18区段相对于1994年和2008年早期活动的氚和3He的演变分布，以阐明东太平洋通风和环流中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首次高质量惰性气体测量，以确定对太平洋溶解气体的气-海交换和昼夜混合的影响，以及冰川融化对绕极深水的贡献。在美国全球海洋碳和重复水文测量计划中，氚-3He是一个2级(“非常理想”)的数据集，它的资金来源独立于核心GO-SHIP计划，但在很大程度上利用并补充了核心GO-SHIP计划进行的测量和装船时间。新的氚-3He和惰性气体数据将结合2016年Go-Ship P18水文和示踪观测(例如，CFCs、SF6、O2)、1994年和2008年以前P18职业的氚-3He数据以及来自Go-Ship和GEOTRACES其他部分的太平洋盆地范围的氚-3He数据来解释。新的示踪剂数据提供了关于东太平洋和南大洋物理和生物地球化学过程的独特和有价值的信息：氚作为一种瞬变示踪剂具有独特的半球不对称性，可用作热带南北水团来源地的诊断示踪剂。氚-氦测年提供了一种在年度到十年的时间尺度上对浅层通风和循环的独特和灵敏的测量方法，不同于其他示踪剂，如CFCs和SF6，给出了浅水中水团的来源、年龄和修改的估计。深水中的氦同位素提供了有关热液羽流来源、扩散和稀释的重要信息，并制约了深水循环模型。稀有气体是海-气交换、水团来源、冰海相互作用、上升流和原地昼夜混合的敏感和明确的示踪物。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.