Collaborative research: US GEOTRACES PMT: Trace-metal concentrations and stable isotopes in the North Pacific

国际GEOTRACES计划的目标是了解许多化学元素及其同位素在海洋中的分布。美国国家科学基金会正在支持2018年美国GEOTRACES在太平洋从阿拉斯加到塔希提岛的采样考察。该奖项将侧重于在这次考察中测量海水、过滤颗粒和大气气溶胶颗粒中的铁（Fe）、镍（Ni）、锌（Zn）、铜（Cu）和镉（Cd）的稳定同位素。微量金属Fe、Ni、Zn、Cu和Cd对海洋生物地球化学和碳循环具有强烈的影响。同位素比率的测量——同一化学元素不同形式的相对丰度——提供了仅通过浓度测量无法获得的见解。研究人员将利用同位素数据更多地了解这些元素对海洋的输入和输出，以及影响它们在海洋中分布的生物过程，从而更好地了解这些金属在海洋碳循环中所起的作用。该奖项还将主办一项国际实验室间比较活动，研究海水中低浓度的Cd同位素比率。该项目将支持一名早期职业研究者，一名博士后研究员，以及本科生和研究生。研究人员将沿着美国GEOTRACES太平洋经向样带（PMT）以高空间分辨率测量δ - 56fe、δ - 60ni、δ - 65cu、δ - 66zn和δ - 114cd。得到的所有五种同位素系统的海洋剖面将使他们能够区分关于控制痕量金属分布的不同观点。关于海洋生物地球化学痕量金属循环的各种各样的假设，解决全球重要性的主题将被探索和测试，包括：1)不同的来源，生产力和出口制度，加上翻转环流，如何控制铁，镍，锌，铜和镉及其同位素在太平洋的分布？2)氧最小带是否作为Cd、Zn、Cu和Ni的汇，同时作为Fe的源？3)向北太平洋供应铁的最重要来源是什么？PMT剖面穿越了两个高营养-低叶绿素（HNLC）区域和两个少营养环流，并横切了海洋中最古老的水域，使研究人员能够使用高分辨率的同位素数据集来研究关于垂直、水平和原位生物地球化学过程对所有五种金属及其同位素分布的影响的相互竞争的假设。气溶胶尘埃，火山和减少边缘沉积物，以及热液喷口，如东太平洋隆起，都被假设为太平洋溶解铁循环的主要贡献者。气溶胶和海洋源附近的铁同位素特征的测量将使这些不同的铁源和过程在向铁有限的表层海洋供应铁的重要性得到识别和量化，特别是对沿PMT剖面的两个HNLC区域至关重要。

The goal of the international GEOTRACES program is to understand the distributions of many chemical elements and their isotopes in the oceans. The National Science Foundation is supporting a U.S. GEOTRACES sampling expedition in the Pacific Ocean 2018, from Alaska to Tahiti. This award will focus on measurement of the stable isotopes of iron (Fe), nickel (Ni), zinc (Zn), copper (Cu), and cadmium (Cd) in seawater, filtered particles, and atmospheric aerosol particles on this expedition. The trace metals Fe, Ni, Zn, Cu, and Cd strongly influence marine biogeochemistry and carbon cycling. Measurements of isotope ratios -- the relative abundance of different forms of the same chemical element -- provide insights not possible from concentration measurements alone. The investigators will use isotope data to learn more about the inputs and outputs of these elements to the ocean as well as the biological processes that influence their distributions within the oceans, leading to greater understanding of the role these metals play in oceanic carbon cycling. The award will also host an international inter-lab comparison exercise for Cd isotope ratios at low concentrations in seawater. The project will support an early career investigator, a postdoctoral researcher, and undergraduate and graduate students. The investigators will measure delta-56Fe, delta-60Ni, delta-65Cu, delta-66Zn, and delta-114Cd at high spatial resolution along the U.S. GEOTRACES Pacific Meridional Transect (PMT). The resulting oceanic sections of all five isotope systems will enable them to distinguish between competing ideas about the controls on trace metal distributions. A wide variety of hypotheses about marine biogeochemical trace metal cycling, addressing topics of global importance will be explored and tested, including: 1) How do different sources, productivity and export regimes, coupled with overturning circulation, control the distribution of Fe, Ni, Zn, Cu and Cd and their isotopes in the Pacific? 2) Do oxygen minimum zones act as sinks for Cd, Zn, Cu and Ni, while acting as sources for Fe? and 3) What sources are most important for supplying Fe to the North Pacific Ocean? The PMT section crosses two high nutrient-low chlorophyll (HNLC) regions and two oligotrophic gyres, as well as transecting the oldest waters in the ocean, allowing the investigators to use high-resolution isotope datasets to investigate competing hypotheses about the effect of vertical, horizontal and in situ biogeochemical processes on the distribution of all five metals and their isotopes. Aerosol dust, volcanogenic and reducing margin sediments, and hydrothermal vents such as the East Pacific Rise have all been hypothesized as major contributors to the dissolved Fe cycle in the Pacific. Measurement of iron isotope signatures in aerosols and near to oceanic sources will enable the identification and quantification the importance of these different iron sources and processes in supplying iron to the iron-limited surface ocean, especially important for the two HNLC regions along the PMT section.