Role of Organic Matter in Determining the Solubility of Atmospherically-Delivered Iron

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The atmospheric delivery of soluble Fe to the ocean is an important process contributing to oceanic primary production and the drawdown of atmospheric CO2. Combustion influenced air masses carry highly soluble Fe, but the reasons for this increased solubility remain unclear despite the importance to global carbon cycling. Acidic organic matter (OM) components (e.g., -COOH groups) can complex with trace metals, yet no study to date has investigated the comprehensive molecular characteristics of aerosol OM for their role as a determinant of Fe solubility. In this project, researchers at Old Dominion University will study the relationship between the molecular characteristics of marine aerosol water soluble OM (WSOM) and Fe solubility. Marine particulate aerosols collected during GEOTRACES cruises will be examined to identify WSOM characteristics that may play a role in delivering soluble and bioavailable Fe to the N. Atlantic Ocean. Aerosol WSOM will be characterized using advanced molecular and chemometric techniques to test whether: (1) continental combustion-influenced aerosol samples show molecular characteristics unique from those of continental dust influenced samples, having characteristics consistent with higher contributions from OM with acidic functional group; (2) aerosol WSOM examined along a gradient of Fe solubility show concurrent changes in the relative magnitude of highly oxygenated compounds and contributions from acidic functional groups; and (3) 2D HMBC NMR reveal unique components in composite continental combustion influenced samples relative to marine and dust-influenced samples, and these unique components include OM with carboxyl functional groups that can bind Fe. This project will be the first of its kind to extensively examine WSOM molecular characteristics and Fe solubility on concurrently collected aerosol samples. The results will be useful for understanding Fe distributions and biogeochemical cycling in the ocean. A potentially transformative aspect of this proposal will be the identification of aerosol WSOM molecular components unique to combustion influenced air masses that have the potential to facilitate aerosol Fe solubility. Broader Impacts: The findings of this project are expected to be highly relevant to oceanic and global biogeochemical cycling of OM and many trace metals that form organic complexes. Combustion-influenced OM associations may help explain patterns in the global oceanic distribution of other trace metals and provide key insights into oceanic processes (e.g., primary production, biological pump). The project would provide a strong interdisciplinary, training and learning environment for the PIs and undergraduate and graduate students at ODU. A PhD student would be involved in all aspects of the project and learn state-of-the-art analytical techniques and gain experience in aspects of project management, data processing, and data presentation