Controls on remote Pacific Ocean aerosol iron solubility: the importance of aerosol source and organic aerosol composition

Iron is an element essential to life that is present at extremely low concentrations in seawater. Over large areas of the ocean, the primary source of iron to ocean ecosystems is from small aerosol particles in the atmosphere that are carried thousands of kilometers from land. In addition, only a small amount of the iron dissolves and becomes available for phytoplankton and other organisms. This project will study iron in aerosol and rainwater samples from the remote North and South Pacific. The outcome will be better understanding of ocean productivity, which ultimately supports ocean economies and human health. The project will support a graduate student who will receive training in fieldwork, laboratory practices and analyses, data analysis, and scientific writing and communication. Work in the North Atlantic indicates a link between iron solubility and the loading of water-soluble organic matter (WSOM), with WSOM characteristics influenced by aerosol provenance. Understanding of how different sources influence aerosol iron solubility over the remote Pacific Ocean is limited by a lack of field studies, particularly in the South Pacific. Modeling studies indicate that Asian dust and anthropogenic aerosols dominate soluble iron supply to the North Pacific, while a much lower input rate to the South Pacific from Australia and South America has a greater relative contribution from wildfire aerosols. This project will take advantage of upcoming basin-scale oceanographic expeditions in the Pacific Ocean to investigate the relationship between iron solubility and WSOM in aerosols from different sources. To improve understanding about controls on soluble Fe supply to the surface ocean, the team will: 1. Collect aerosol and rain samples from the remote North and South Pacific during three U.S. GO-SHIP sections (P16S/C, P16N, P06) and use source-specific tracers to relate total and soluble iron loading to relative source contributions. 2. Identify and quantify the relationship between Fe solubility and the relative loading of WSOM in Pacific aerosols. 3. Use proton nuclear magnetic resonance (NMR) spectroscopy and Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry to identify source-diagnostic WSOM molecular signatures (including the identification of iron-bound WSOM ligands) in aerosols. 4. Calculate atmospheric deposition fluxes of total and soluble iron and other trace elements to the remote Pacific Ocean based on aerosol size distributions and precipitation rate. 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. NSF Award ID: 2547395 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Christopher Marsay | Institution: University of Delaware, NEWARK, DE | Award Amount: $972,945 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2547395 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2547395.html