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

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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.