GEOTRACES Pacific Section: Measurement of Helium Isotopes, Tritium, Noble Gases, and Radiocarbon

海洋环境中微量元素和同位素（TEI）的地球化学循环是全球变化背景下的一个重要研究领域，推动了国际GEOTRACES计划。已知某些微量元素作为微量营养素在生物循环中，特别是在海洋环境中的酶和催化过程中发挥潜在的重要作用。放射性同位素、瞬变示踪剂和惰性气体是这些和相关过程以及海洋的有价值的示踪剂吗？海洋与大气和固体地球的相互作用，反过来又在塑造海洋中的许多微量元素分布中发挥作用。 根据GEOTRACES科学计划，GEOTRACES方案的指导使命是"查明控制海洋中关键微量元素和同位素分布的过程并量化通量"。 GEOTRACES的关键观测战略是对关键TEIs进行国际协调的全球规模海洋调查。美国GEOTRACES的第二个部分定于2013年在南太平洋东部进行，目的是描述最低含氧区以及从东太平洋海隆向西延伸的主要深海热液羽流的关键过程。为了帮助实现这些目标，在这笔赠款的支持下，伍兹霍尔海洋研究所的一个研究小组将与东南太平洋考察队的其他GEOTRACES调查人员合作，测量一套用于解释其余天气TEI数据的示踪剂。 具体来说，该小组将对稀有气体、氦同位素、氚和放射性碳进行测量，以便：（1）量化OMZ中的通风、循环和透环混合，以估计关键TEI的通量和转化率;（2）确定最小氧区（OMZ）在一系列时间尺度上的上升流速率，以限制地球化学重要属性的通量;（3）利用氦-3作为通量计估算关键TEI的热液通量，并利用氦-3作为热液羽流下游稀释的量度;（4）利用放射性碳估算关键TEI的深海再矿化速率;（5）探索热液过程对TEI分布的离轴贡献的证据。集体的努力将使海洋地球化学家了解机械和定量的各种物理，化学和生物过程如何加入，以确定在ocean.Broader影响的分布：有人认为，人类活动对全球循环的许多元素正在出现显着。正如国际地球跟踪科学计划所概述的那样，这项活动的更广泛影响包括对海洋环境的地球化学状态进行重要的"基线快照"，以及从数量上改进对海洋环境重要过程的定性和了解。这两个方面都为改进模式和定量预测海洋在全球变化和气候中的反应和作用奠定了基础，特别是在人为强迫方面。例如，最近关于"海洋脱氧"的证据对海洋生物反应具有深远的影响。特别是，海洋有机隔离区的演变状态是一个重要的地球化学"气候金丝雀"。诊断痕量金属动力学和对不断变化的氧化还原条件的反应的一个关键益处是提高耦合海洋-大气地球化学模型对全球变化的预测能力。

The biogeochemical cycling of trace elements and isotopes (TEIs) in the marine environment is an important research area within the context of global change that motivates the International GEOTRACES program. Some trace elements are known to play potentially important roles as micronutrients in biological cycling, particularly in regard to enzymatic and catalytic processes in the marine environment. Radioisotopes, transient tracers, and noble gases are valuable tracers of these and related processes, and of the ocean?s interaction with the atmosphere and the solid earth, which in turn play a role in shaping many trace element distributions within the ocean. According to the GEOTRACES Science Plan, 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 TEIs. The second US GEOTRACES section, set for the Eastern South Pacific in 2013, is aimed at the characterization of key processes in an oxygen minimum zone (OMZ), as well as a major abyssal hydrothermal plume extending westward from the East Pacific Rise. To help achieve these goals, with support from this grant, a research team at the Woods Hole Oceanographic Institution will collaborate with other GEOTRACES investigators on the Eastern South Pacific expedition to measure a suite of tracers useful for interpreting the rest of the synoptic TEI data. Specifically, the team will make measurements of the noble gases, helium isotopes, tritium, and radiocarbon include in order to: (1) quantify ventilation, circulation, and diapycnal mixing in the OMZ to enable estimation of fluxes and transformation rates of key TEIs; (2) determine upwelling rates in the oxygen minimum zone (OMZ) over a range of timescales to constrain the fluxes of biogeochemically important properties; (3) estimate hydrothermal fluxes of key TEIs using 3He as a flux gauge, and also use 3He as a measure of downstream dilution in the hydrothermal plume; (4) use radiocarbon to estimate abyssal remineralization rates for key TEIs; and (5) probe for evidence of off-axis contribution of hydrothermal processes to TEI distribution. The collective effort will allow marine geochemists to understand mechanistically and quantitatively how a variety of physical, chemical, and biological processes join to determine the distribtuion of TEIs in the ocean.Broader Impacts: It has been argued that anthropogenic influence on the global cycles of many elements is emerging as significant. As outlined in the International GEOTRACES Science Plan, the broader impacts of this activity include both an important "baseline snapshot" of the biogeochemical state of the oceanic environment, and a quantitative improvement in the characterization and understanding of important processes in the marine environment. Both of these build a foundation for improved models and quantitative predictions of the oceanic response and role in global change and climate, particularly with anthropogenic forcing. For example, recent evidence of "ocean deoxygenation" has profound implications for marine biologic response. In particular, the evolving state of marine OMZs represents an important biogeochemical "climate canary". A key benefit of diagnosing trace metal dynamics and response to changing redox conditions is the improvement in prognostic capabilities of coupled ocean-atmosphere biogeochemical models for global change.