Collaborative Research: US GEOTRACES GP17-OCE and GP17-ANT: Export and remineralization rates of bioactive and particle reactive trace elements using thorium-234

国际GEOTRACES计划的首要目标是“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的敏感性。”这些微量元素在海洋中的浓度极低，但对海洋生物，特别是海洋浮游植物的生长和分布起着关键作用。此外，许多痕量元素作为污染物进行研究很重要，例如铜和铅，它们的含量过高可能对海洋生物有害。因此，需要对痕量金属源和金属汇进行研究。为了实现这一目标，该项目旨在测量这些微量元素在海洋食物网中循环的速度，特别是当它们通过海洋雪运输时，即缓慢地将携带这些微量元素和碳的海洋颗粒沉淀到深海。这项工作将在即将到来的两次美国GEOTRACES探险中进行，分别前往南太平洋、南大洋和阿蒙森海。该项目将为两名博士后研究人员提供培训，一名专注于样本分析，一名专注于建模。为了开展这项研究，这项提议将使用自然产生的粒子反应性放射性核素钍-234(234，半衰期=24.1d)来量化痕量元素和同位素清除、停留时间、从表层海洋输出的粒子及其进入深海的衰减方面的变异性。该项目将对极端的生物地理和痕量元素梯度进行采样，范围从低粉尘、低生产率的南太平洋(GP17-OCE)的清澈水域到南大洋“最绿色”的高生产率阿蒙森海及其波尼亚(GP17-ANT)。评估这些空间和垂直梯度需要在每个站点进行234次采样(n=66个投射深度x 13个深度)，并测量粒子的TEI/234比率(n=43 x 8深度x 2个大小类别)。该项目的结果将使人们更好地理解如何通过清除下沉颗粒和重新矿化下沉颗粒来修改微量元素。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The overarching goal of the international GEOTRACES Program 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 environmental conditions.” These trace elements exist at exceeding low concentrations in the ocean, yet play a key role in the growth and distribution of marine organisms, in particular marine phytoplankton. In addition, many trace elements are important to study as pollutants, such as copper and lead, which at high levels can be harmful to marine life. Thus, studies of the trace metal sources and sinks are needed. To meet this goal, the project is designed to measure how quickly these trace elements are cycled through marine food webs, in particular as they are transported by marine snow, i.e. slowly settling marine particles that carry these trace elements and carbon to the deep sea. The work will be conducted aboard two upcoming US GEOTRACES expeditions to the South Pacific, Southern Ocean, and Amundsen Sea. The project will provide training for two postdoctoral investigators, one focused on sample analysis and one on the modeling. To carry out this study, this proposal will use the naturally occurring particle reactive radionuclide Thorium-234 (234Th, half-life = 24.1 d) to quantify variability in trace elements and isotopes scavenging, residence times, and particle export from the surface ocean and their attenuation into the deep sea. This project will sample across extreme biogeographical and trace elemental gradients that range from the clear waters of the low dust, low productivity South Pacific (GP17-OCE) to the “greenest” high productivity Amundsen Sea and its polynyas in the Southern Ocean (GP17-ANT). Assessing these spatial and vertical gradients requires 234Th sampling at every station (n=66 casts x 13 depths) and measuring the TEI/234Th ratio on particles (n=43 x 8 depths x 2 size classes). There results of this project will lead to an increased understanding of how the trace elements are modified by removal and regeneration associated with scavenging on to, and remineralization off of, sinking particles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.