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

海洋环境中痕量元素和同位素(TEI)的生物地球化学循环是全球变化背景下的一个重要研究领域，它推动了国际地学研究计划。已知一些微量元素作为微量营养素在生物循环中可能发挥重要作用，特别是在海洋环境中的酶和催化过程中。放射性同位素、瞬时示踪剂和惰性气体是这些过程和相关过程的宝贵示踪物，也是海洋与大气和固体地球相互作用的宝贵示踪物，这些相互作用反过来又在塑造海洋中的许多微量元素分布方面发挥作用。根据GEOTRACES科学计划，GEOTRACES计划的指导任务是“确定控制海洋中关键微量元素和同位素分布的过程和通量”。GEOTRACES的关键观测战略是对关键的TEI进行国际协调的全球规模海洋调查。定于2013年在东南太平洋东部举行的美国地质灾害监测系统第二个部分，旨在描述氧气最小区(OMZ)以及从东太平洋隆起向西延伸的主要深海热液羽流中的关键过程。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在东南太平洋探险中与GEOTRACES的其他研究人员合作，测量一套有助于解释其余天气学TEI数据的示踪剂。具体地说，该小组将对惰性气体、氦同位素、氚和放射性碳进行测量，以便：(1)量化OMZ中的通风、环流和昼夜混合，以便能够估计关键TEI的通量和转化率；(2)在一系列时间尺度上确定氧最小区(OMZ)的上升率，以限制生物地球化学重要性质的通量；(3)使用3He作为通量计估计关键TEI的热液通量，并使用3He作为热液羽流中下游稀释的测量；(4)使用放射性碳估计关键TEI的珊瑚再矿化率；(5)寻找热液作用对TEI分布的离轴贡献证据。这一集体努力将使海洋地球化学家能够从机械和定量上了解各种物理、化学和生物过程是如何结合在一起来确定海洋中TEI的分布的。广泛的影响：有人认为，人类对许多元素的全球循环的影响正在显现为重要的。正如国际地球科学计划所概述的那样，这项活动的更广泛影响包括海洋环境生物地球化学状态的重要“基线快照”，以及在描述和了解海洋环境中的重要过程方面的数量改进。这两点都为改进模型和定量预测海洋在全球变化和气候变化中的反应和作用奠定了基础，特别是在人为强迫的情况下。例如，最近关于“海洋除氧”的证据对海洋生物的反应有着深远的影响。特别是，海洋OMZ的演变状态代表了一个重要的生物地球化学“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响应的一个关键好处是改善了全球变化海洋-大气生物地球化学耦合模式的预测能力。

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.