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计划的总体目标是“确定控制海洋中关键微量元素和同位素分布的过程和量化通量，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以极低的浓度存在，但在海洋生物，特别是海洋浮游植物的生长和分布中起着关键作用。此外，许多微量元素作为污染物对研究很重要，如铜和铅，它们在高水平时可能对海洋生物有害。因此，需要对痕量金属源和汇进行研究。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，特别是当它们被海洋雪运输时，即缓慢沉降的海洋颗粒将这些微量元素和碳带到深海。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提供培训，一名专注于样本分析，另一名专注于建模。为了开展这项研究，本提案将使用天然存在的粒子反应性放射性核素钍-234（234，半衰期= 24.1 d）来量化微量元素和同位素清除、停留时间以及粒子从海洋表面输出及其衰减到深海的变化。该项目将对极端生物地理和微量元素梯度进行采样，范围从低粉尘、低生产力的南太平洋（GP17-OCE）的清澈水域到“最绿色”的高生产力阿蒙森海及其南大洋的多冰湖（GP17-ANT）。评估这些空间和垂直梯度需要在每个站点进行第234次采样（n=66个铸件x 13个深度），并测量颗粒的TEI/234比（n=43 x 8个深度x 2个尺寸类别）。这个项目的结果将使我们进一步了解微量元素是如何通过清除和再生来修饰的，这些清除和再生与下沉颗粒的再矿化有关。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.