GEOTRACES Peru-Tahiti section: Measurement of 7Be as a Tracer of Upper Ocean Processes

在海洋中，微量元素作为营养物质、人类活动的污染物，甚至是当前和过去的海洋过程的便捷示踪剂，发挥着不同的作用。它们的生物地球化学循环对海洋碳循环和生态系统动态以及全球气候变化都有重大影响。许多影响海洋中痕量元素分布和行为的过程无法直接观测，因此各种地球化学示踪剂被用来提供对其速率和途径的重要限制。铍-7(Be7)是一种宇宙源(即在高层大气中产生的)放射性核素，由于其半衰期(53.3d)，可用于研究发生在季节性时间尺度上的环境过程。这个时间尺度对生物生产、营养再生和大气沉积的研究很重要，仅举几例。在这个项目中，迈阿密大学的一个研究小组将在2013年对从秘鲁到塔希提岛的美国地学横断面上的Be7水柱进行测量。国际地球物理研究计划(美国计划是该计划的一部分)的使命是“确定控制海洋中关键微量元素和同位素分布的过程和通量，并确定这些分布对环境条件变化的敏感性。”作为多机构美国地球科学计划太平洋行动的一部分，迈阿密团队将处理在地球科学计划内制定的主要任务。具体地说，它们将：(1)对影响所测量的感兴趣元素(TEI)分布的基本输送过程提供现实的估计；它们将使用BE7的水柱测量作为物理过程的示踪剂，例如混合和上升流，这将重新分布生物活性物种；(2)开发和应用新的BE7方法，以量化参加该活动的其他研究小组测量的TEI的大气沉积。对巡航航道沿线地表水和低层大气中Be7的测量将提供对相关TEI大气输入的估计。大气对全球海洋的输入是众多化学物质的重要预算组成部分，但很难加以限制。在这项工作中产生的数据将可用于气溶胶沉积模型的地面真实和痕量元素的大气输入。更广泛的影响：拟议的工作是为了支持GEOTRACES计划，因此有助于该计划的许多广泛的智力目标。能够提供对相关TEI的大气输入的估计是一个重要的例子，这一能力将在地球物理轨道以外的未来对该领域作出广泛贡献，包括了解人为对海洋的影响。研究生的教育和培训将是这项研究的重要组成部分。

In the ocean, trace elements function variously as nutrients, as contaminants from human activity, and even as convenient tracers of current and past oceanographic processes. Their biogeochemical cycling has major impacts on the ocean carbon cycle and ecosystem dynamics as well as on global climate change. Many processes influencing the distribution and behavior of trace elements in the ocean cannot be directly observed, so consequently a variety of geochemical tracers are used to provide important constraints on their rates and pathways. Beryllium-7 (Be7) is a cosmogenic (i.e., produced in the upper atmosphere) radionuclide that, because of its half-life (53.3d), can be used in the study of environmental processes occurring over seasonal timescales. This timescale is important to studies of biological production, nutrient regeneration, and atmospheric deposition, to name a few. In this project, a research team from the University of Miami will make measurements of water column Be7 along the U.S.GEOTRACES transect from Peru to Tahiti in 2013. The mission of the International GEOTRACES Program (of which the US program is a component) is "to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions." As part of the multi-institutional U.S.GEOTRACES Pacific campaign, the Miami team will address key tasks formulated within the GEOTRACES Science Plan. Specifically, they will: (1) provide realistic estimates of the underlying transport processes influencing measured trace elements of interest (TEI) distributions; they will use water column measurements of Be7 as a tracer of physical processes, such as mixing and upwelling, which redistribute biologically active species; and (2) develop and apply new Be7 methods for quantifying the atmospheric deposition of TEIs measured by other research teams participating in the campaign. Measurements of Be7 in the surface waters and in the lower atmosphere along the cruise track will provide estimates of the atmospheric input of relevant TEIs. The atmospheric input into the global ocean is an important budgetary component of numerous chemical species, yet is very difficult to constrain. The data generated in this work will be available to allow ground-truthing of aerosol deposition models and the atmospheric input of trace elements. Broader impacts: The proposed work is in support of the GEOTRACES program, and as such contributes to many of the broad intellectual objectives of that program. The ability to provide estimates of the atmospheric input of relevant TEIs is an important example, and one that will contribute widely to the field in the future beyond GEOTRACES, including understanding anthropogenic impacts on the oceans. Education and training of graduate students will be essential components of this research.