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

由于流入阿蒙森海的冰川迅速融化，毗邻南极洲的阿蒙森海得到了越来越多的关注。虽然科学和媒体的大部分注意力都集中在冰川融化将如何影响海平面上升上，但这也给海洋化学和生物带来了重要的后果。阿蒙森海部分地区的光合作用速率是南极洲周围所有开放水域中最高的，这可能是因为融化的冰川提供了铁等必要的营养物质。详细了解冰川融化如何影响包括铁在内的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。本项目旨在通过重点研究海洋颗粒在微量营养物质水平的供应和去除中所起的作用来研究这一系统。海洋颗粒包括海水中来自生物、化学和地质过程的所有悬浮固体物质。一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。调查人员将确定阿蒙森海中海洋颗粒物的浓度和化学成分，以了解哪些类型的颗粒提供营养物质，哪些类型的颗粒去除海水中的营养物质。这项工作将阐明在这个快速变化的世界地区，颗粒在营养物质的供应和去除中所起的重要作用。这项工作将培训来自西海岸(加州大学圣克鲁斯分校)、东北部(罗德岛大学)和东南部(佐治亚大学)的三所美国公立院校的本科生和研究生。该项目还将支持一名记者参与这次探险，并进行宣传、报道和撰写故事，向公众传达这一合作项目的结果。阿蒙森海是一个经典的“温暖的南极大陆架”，温暖的环极深水(CDW)侵入大陆架，导致南极边缘最高的冰川基面融化速率。美国GEOTRACES计划已经得到资助，将在阿蒙森海进行为期60天的研究巡航，携带地球化学工具来研究这种高融化的生物地球化学后果。颗粒是所有GEOTRACES航段巡航的关键参数，因为它们在供应、内部循环和清除许多痕量元素和同位素(TEI)方面非常重要。之前前往阿蒙森海的航行表明，在受融水影响的地区大量存在的颗粒铁可能有助于推动阿蒙森地区的高NPP。颗粒在清除溶解的铁和其他颗粒反应性TEI的过程中也起着至关重要的作用。事实上，模型已经表明，到目前为止，颗粒清除是溶解铁(DFE)的最大损失项，甚至超过了整个水柱的生物吸收。到目前为止，颗粒仅被表示为颗粒有机物(POM)。除了POM外，还包括其他类型的颗粒可能对清除作用很重要：例如，与包括POM在内的其他颗粒类型相比，铁和锰(氢氧化物)氧化物在清除某些TEI方面的效率要高出1-3个数量级。因此，颗粒的组成，而不仅仅是它们的浓度，对于清除TEI很重要。为了解决对阿蒙森海颗粒生物地球化学认识上的这一差距，该项目有以下三个主要目标：1)确定主要和次要相(颗粒有机碳、蛋白石、CaCO3、致石颗粒、铁氧化物、锰氧化物)的分布，以及通过现场过滤收集的粒度分级颗粒的微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，评估其作为TEIs的源和汇的作用3)检查影响形成、反应活性、阿蒙森海中锰氧化物的稳定性这一裁决反映了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 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.