GEOTRACES Atlantic Section: Measurement of Helium Isotopes and Tritium

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。GEOTRACES计划的指导使命是确定控制海洋中关键微量元素和同位素分布的过程和量化通量。GEOTRACES的主要观测战略是对关键微量元素和同位素（TEI）进行国际协调的全球规模海洋调查，作为该调查的一部分，美国的第一个部分位于北大西洋。了解速率和通量是开发TEIs海洋生物地球化学循环的机制和预测模型的重要一步，特别是在全球变化（过去和未来）的框架内。我们对大尺度海洋速率和通量的了解，大部分是从放射性和瞬态示踪剂分布的观测和模拟中推断出来的。测量适当的瞬态示踪剂以及核心TEI将是实现GEOTRACES目标的有效策略。在该项目中，伍兹霍尔海洋研究所的研究人员将进行氦同位素和氚测量，为在美国GEOTRACES第一个全球调查部分进行的更重要的TEI测量提供有用的地球化学速率信息。氚和3 He测量可以对该计划做出的主要贡献包括：（1）在MOC中量化渡越时间尺度和TEI稀释：3 H和3 He是用于确定西部边界深部电流示踪剂传输速率和内部混合稀释尺度的有用示踪剂，这是许多TEI的重要问题;（2）浅水计时器：使用氚-3He钟，可以确定流体包在6个月至几十年的时间尺度上俯冲所经过的时间;（3）TEI温跃层回流计：3 He是一种独特的“类营养物”瞬态示踪剂，可用作“通量计”，以确定温跃层化TEI返回上层海洋的速率;（4）测量TEI热液稀释比例：在热液活动期间注入的火山3 He是这些羽流中稀释的强大保守示踪剂，允许诊断某些TEI中的非保守行为，并允许与盆地和全球尺度上的热液活动相关的通量估计。 更广泛的影响：拟议的工作是为了支持GEOTRACES计划，因此有助于该计划所支持的更广泛的社会目标和知识目标。与此相关的主要问题涉及了解碳循环和预测/减缓气候变化，以及海洋食物网和人类活动对海洋的影响。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The guiding mission of the GEOTRACES program is to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean. The key observational strategy for GEOTRACES is an internationally-coordinated global-scale ocean survey of key trace elements and isotopes (TEIs), and the first U.S. section as part of that survey is in the North Atlantic. Knowing rates and fluxes is a vital step in the development of mechanistic and predictive models of ocean biogeochemical cycles of TEIs, particularly within the framework of global change (both past and future). Much of what we have learned about large scale oceanic rates and fluxes has been inferred from the observation and modeling of tracer distributions, both radioactive and transient. Measurement of appropriate transient tracers alongside of core TEIs would be an effective strategy for achieving GEOTRACES goals. In this project, researchers at the Woods Hole Oceanographic Institution will make helium isotope and tritium measurements to provide useful biogeochemical rate information for the more centrally important TEI measurements made on the first U.S. GEOTRACES global survey section. The primary contributions that tritium and 3He measurements can make to the program include: (1) Quantifying transit timescales and TEI dilution in the MOC: 3H and 3He are useful tracers for determining deep western boundary current tracer transport rates and interior mixing dilution scales, an important issue for many TEIs; (2) A shallow water chronometer: Using the tritium-3He clock, the time elapsed since fluid parcels have been subducted on timescales ranging from 6 months to several decades can be determined; (3) A TEI thermocline reflux gauge: 3He is a unique "nutrient-like" transient tracer that can be used as a "flux gauge" to determine the rates at which thermocline-remineralized TEIs are returned to the upper ocean; and (4) Gauging TEI hydrothermal dilution scales: Volcanic 3He injected during hydrothermal activity is a powerful conservative tracer of dilution in these plumes, allowing diagnosis of nonconservative behavior in some TEIs, and permitting flux estimates associated with hydrothermal activity on basin and global scale. Broader Impacts: The proposed work is in support of the GEOTRACES program, and as such contributes to the broader societal goals and intellectual objectives espoused by that program. The primary issues related to this are pertinent to understanding the carbon cycle and predicting/mitigating climate change, as well as the marine food web and anthropogenic impacts on the oceans.