Collaborative Research (OSU, USC, RU): Continental Shelf Diagenesis II: The Importance of Increasing Oceanic Hypoxia to Coastal Iron Supply and the Ocean's Iron Isotope Composition

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AbstractCoastal zone hypoxia (oxygen depletion) has both natural and, increasingly, anthropogenic dimensions that can lead to host of changes to the biogeochemical processes taking place on continental shelves. Continental shelf regions are well known to be important transition zones between terrestrial sources and the deep ocean. The objectives of this collaborative study are to determine the efflux rates of iron from coastal zone and continental shelf sediments to overlying water columns during the development of seasonal anoxia cycles. The underlying hypothesis being tested at selected study sites in the Gulf of Mexico, and on previously sampled materials from Peru and Namibia continental margins, is that the redox gradients occurring in these shelf sediments will deliver both increasing flux rates and with characteristically isotopically lighter Fe signatures as anoxia develops. If the extent of anoxia transitions to a sulfidic sediment regime, the benthic iron flux may decrease in a negative feedback loop due to solubility constraints, but with even lighter isotopic Fe escaping to the water column. A better understanding of the diagenetically delivered flux of iron, an essential micronutrient for phytoplankton growth, from sediments is sought to account for the global balance of ocean productivity under changing oceanic conditions. The ability of Fe-isotopic systematics to trace coastal benthic iron sources is a potentially transformative outcome of this research. The work will also strengthen the international collaboration between US, and German researchers, and provide an opportunity to develop these ideas with methodologies such as benthic chambers for bottom water sampling, as well as sediment pore fluids and core incubations, and water column isotopic studies. A range of educational and outreach activities will also be carried out.