Collaborative Research: US GEOTRACES GP17-ANT: Characterizing the composition, scavenging efficiency and bioavailability of size fractionated particles

南极洲附近的阿蒙森海因冰川迅速融化而受到越来越多的关注。虽然大多数科学和媒体的注意力都集中在冰川融化将如何影响海平面上升，但对海洋化学和生物学也有重要影响。 阿蒙森海的部分地区在南极洲周围的所有开放水域中具有最高的光合作用速率，这可能是因为融化的冰川提供了铁等必需的营养物质。 详细了解冰川融化如何影响铁等营养物质的供应和去除，对于预测冰川融化的生物、化学和气候后果是必要的。本项目旨在通过关注海洋颗粒物在微量营养物质供应和去除中的作用来研究这一系统。 海洋颗粒物包括海水中所有悬浮的固体物质，它们来自生物、化学和地质过程。 某些类型的海洋颗粒为海水提供营养物质，而其他类型的海洋颗粒则从海水中去除营养物质。 研究人员将确定阿蒙森海海洋颗粒的浓度和化学成分，以了解哪些类型的供应和哪些类型的去除海水中的营养物质。 这项工作将阐明颗粒在世界这个快速变化的地区的营养物质供应和去除中的重要作用。 这项工作将培训来自美国西海岸（加州大学，圣克鲁斯），东北（罗得岛大学）和东南（格鲁吉亚大学）三所公立机构的本科生和研究生。该项目还将支持一名记者参与此次巡航，并对此次探险进行宣传、报道和撰写报道，以向公众传达这一合作项目的成果。阿蒙森海是一个典型的“温暖的南极大陆架”，温暖的绕极深水（CDW）侵入大陆架，导致南极边缘最高的冰川基底融化率。美国的GEOTRACES计划已获得资助，在阿蒙森海进行为期60天的研究巡航，以利用地球化学工具研究这种高熔体的地球化学后果。颗粒是所有GEOTRACES部分巡航的关键参数，因为它们在供应，内部循环和许多微量元素和同位素（TEI）的去除方面非常重要。以前对阿蒙森海的考察表明，在受融水影响的地区富含的颗粒状铁可能有助于为阿蒙森海的高NPP提供燃料。颗粒还通过清除在去除溶解的Fe和其他颗粒反应性TEI中发挥重要作用。事实上，模型表明，颗粒清除是迄今为止溶解铁（dFe）的最大损失项，甚至大于生物吸收时，在整个水柱集成。到目前为止，颗粒物仅被表示为颗粒有机物（POM）。除了POM之外，包含其他颗粒类型对于清除可能是重要的：例如，Fe和Mn（羟基）氧化物已经显示出与其他颗粒类型（包括POM）相比，在清除一些TEI方面更有效1-3个数量级。因此，颗粒的组成，而不仅仅是它们的浓度，对于TEI的清除去除是重要的。为了弥补对阿蒙森海颗粒地球化学认识的这一差距，该项目有以下三个主要目标：1）确定主相和次相的分布（颗粒有机碳、蛋白石、CaCO 3、成石颗粒、羟基氧化铁、锰氧化物），以及通过现场过滤收集的粒度分级颗粒的痕量元素和悬浮颗粒质量浓度2）确定阿蒙森海颗粒铁的形态和生物有效性，以评估其作为TEI源和汇的作用3）检查影响TEI形成，反应性，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准。

The Amundsen Sea adjacent to Antarctica has gained increasing attention because of rapid melting of glaciers that drain into it. While most of the scientific and media attention has focused on how melting glaciers will affect sea level rise, there are also important consequences for ocean chemistry and biology. Parts of the Amundsen Sea have the highest rates of photosynthesis of all open water regions surrounding Antarctica, and this may be because melting glaciers are supplying essential nutrients such as iron. A detailed understanding of how melting glaciers affect the supply and removal of nutrients including iron is necessary to predict the biological, chemical, and climate consequences of melting glaciers.This project aims to study this system by focusing on the role that marine particles play in the supply and removal of trace nutrient levels. Marine particles include all suspended, solid material in seawater that derive from biological, chemical, and geological processes. Some types of marine particles supply nutrients to seawater, whereas other types remove nutrients from seawater. The investigators will determine the concentrations and chemical compositions of marine particles in the Amundsen Sea in order to understand which types supply and which types remove nutrients from seawater. This work will clarify the essential role of particles in the supply and removal of nutrients in this quickly changing part of the world. This work will train undergraduate and graduate students from three public US institutions in the west coast (University of California, Santa Cruz), northeast (University of Rhode Island), and southeast (University of Georgia). This project will also support a journalist to participate in the cruise and pitch, report, and write stories from the expedition to communicate the results of this collaborative project to the public.The Amundsen Sea is a classic “warm Antarctic continental shelf”, where intrusions of warm Circumpolar Deep Water (CDW) onto the shelf have resulted in the highest glacial basal melt rates on the Antarctic Margin. The US GEOTRACES program has been funded for a 60-day research cruise in the Amundsen Sea to bring geochemical tools to study the biogeochemical consequences of this high melt. Particles are a key parameter for all GEOTRACES section cruises because of their importance in the supply, internal cycling, and removal of many trace elements and isotopes (TEIs). Previous cruises to the Amundsen Sea have suggested that particulate Fe, abundant in meltwater-influenced regions, may be helping to fuel the high NPP in the Amundsen. Particles also play an essential role in the removal of dissolved Fe and other particle-reactive TEIs via scavenging. Indeed, models have shown that scavenging by particles is by far the largest loss term for dissolved Fe (dFe), even larger than biological uptake when integrated over the entire water column. So far, particles have been represented only as particulate organic matter (POM). The inclusion of other particle types besides POM is likely important for scavenging: for example, Fe and Mn (oxyhydr)oxides have been shown to be 1-3 orders of magnitude more efficient at scavenging some TEIs compared to other particle types, including POM. Thus, the composition of particles, not just their concentration, is important for the scavenging removal of TEIs. To address this gap in the understanding of particle biogeochemistry in the Amundsen Sea, this project has the following three main goals: 1) To determine the distributions of major and minor phases (particulate organic carbon, opal, CaCO3, lithogenic particles, Fe oxyhydroxides, Mn oxides), and trace element and suspended particulate mass concentrations of size fractionated particles collected by in-situ filtration2) To determine the speciation and bioavailability of particulate Fe in the Amundsen Sea to assess its role as a source and sink of TEIs 3) To examine the factors affecting the formation, reactivity, and stability of Mn oxides in the Amundsen SeaThis 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.