Collaborative Research: US GEOTRACES GP17-ANT: Answering key questions in marine particle trace element biogeochemistry in the Amundsen Sea

国际GEOTRACES项目的目标是了解海洋中微量化学元素及其同位素的分布。该项目将生成一个包含悬浮颗粒和表面沉积物样本的40种微量元素的数据集，这些样本是由GEOTRACES GP17-ANT号在南极洲西部阿蒙森海巡航时收集的。阿蒙森海拥有整个南极洲单位面积上产量最高的冰湖，其生物碳吸收量比南大洋的平均水平高出十倍。在过去的30年里，该地区已成为淡水输入增加的主要地点，因为南极洲西部冰川融化速度最快，为阿蒙森海提供了大量且不断增加的淡水。这一区域对全球海平面上升的主要贡献是有案可稽的，但融化水和相关化学成分加速增加对南极陆架水域生物地球化学的影响，特别是对微量元素循环的影响，还没有得到全面的调查。针对阿蒙森海生物地球化学系统的四个关键组成部分的假设将进行测试，结果将与其他GP17-ANT研究人员提出的补充努力密切吻合。该项目将支持一名研究生和几名本科生实习生，重点是扩大对STEM的参与。研究人员还将与已建立的项目合作，为初高中学生创造有意义的校外科学体验。该项目的目的是量化和解释大约500个样本中颗粒微量元素的分布，这些样本覆盖了阿蒙森海大陆架的一大片区域，包括受五个主要冰架影响的水域，以及在西经100°和135°、南纬67°以南的邻近铁有限的南大洋水域。研究人员将使用粒度分馏样品收集、总酸消化和弱酸浸出，以及完善的质谱方法来确定浓度并探测颗粒微量元素的物理化学状态。研究小组将利用这些新数据研究以下问题：1)浮游植物在经历不同程度的铁胁迫时在上层水柱中驱动元素循环的作用，重点关注阿蒙森海陆架上的优势类群褐藻和硅藻；2)“融水泵”，从冰架空洞中产生强劲而富含颗粒的流出物；(3)再悬浮沉积物的底部网状层作为一个反应带，决定了沉积古记录的组成，并调节了沉积-水边界的化学通量；4)稀土元素（REE），该团队提出，在地质多样性的冰川流域中，稀土元素携带着独特的陆源颗粒来源的地球化学信息，还包括一个不稳定的颗粒分数，其大小和元素间比率可以作为元素清除强度的相对指标，可以应用于预测其他颗粒活性元素的最大清除区域。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 goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. This project will generate a dataset of 40 trace elements on suspended particles and surface sediment samples collected on the GEOTRACES GP17-ANT cruise to the Amundsen Sea, West Antarctica. The Amundsen Sea hosts the most productive polynya per unit area in all of Antarctica, with biological carbon uptake ten times higher than the average for the Southern Ocean. Over the past 30 years, this region has become a primary locus of increased freshwater input, as the fastest melting glaciers in West Antarctica deliver huge and increasing volumes of freshwater to the Amundsen Sea. The major contribution of this region to global sea level rise is well documented, but the impact of accelerated additions of meltwater and associated chemical constituents on the biogeochemistry of the Antarctic shelf waters, and in particular on the cycling of trace elements, has not received comprehensive investigation. Hypotheses addressing four key components of the biogeochemical system in the Amundsen Sea will be tested, and results will closely mesh with complementary efforts proposed by other GP17-ANT investigators. The project will support a graduate student and several undergraduate interns, with a focus on broadening participation in STEM. The investigators will also work with established programs to create meaningful out-of-school science experiences for middle and high school students.The aim of the project is to quantify and interpret the distributions of particulate trace elements in approximately 500 samples covering a large swath of the Amundsen Sea shelf, including waters influenced by five major ice shelves, and in the adjacent iron-limited Southern Ocean waters bounded by 100°W and 135°W, and south of 67°S. The investigators will use size-fractionated sample collection, total acid digestion and weak acid leaching, and well-established mass spectrometric methods to determine concentrations and probe the physico-chemical state of the particulate trace elements. The team will use the new data to investigate the following issues: 1) the role of phytoplankton, with a focus on Phaeocystis and diatoms, dominant taxa on the Amundsen Sea shelf, in driving element cycling in the upper water column while experiencing variable degrees of iron stress; 2) the “meltwater pump” which generates vigorous and particle-rich outflow from ice shelf cavities; 3) the bottom nepheloid layer of resuspended sediments as a reaction zone that determines the composition of the sedimentary paleo-record and also modulates of chemical fluxes at the sediment-water boundary; and 4) the rare earth elements (REE), which the team proposes carry unique geochemical information about terrigenous particle provenance among the geologically diverse glacial drainage regions, and also includes a labile particulate fraction whose magnitude and inter-element ratios may serve as a relative index of element scavenging intensity that can be applied to predict regions of maximal scavenging for other particle-reactive elements.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.