Bottom boundary layer mediation of chemical fluxes from ocean margins

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Marine sediments are an important source of essential micronutrients to the ocean, but measuring these inputs is problematic. I aim to observe and understand the behavior of micronutrient inputs, in particular iron, close to the seafloor, where exchanges between sediments and seawater are thought to mediate the uptake of carbon via photosynthesis in the surface ocean. Refining this critical source to the ocean is needed to improved ocean-coupled models of the Earth's climate. A key aspect of this work will be to collect samples of dissolved and suspended particulate material in vertical transects close to the seabed, where the physical mixing and chemical exchanges in the ocean are completely different from the ocean interior. Chemical processes in this 'bottom boundary layer' are largely unknown, because sampling it from the ocean surface is difficult; large distances from a research vessel propagates inaccuracy close to the seafloor and risks damage or loss of costly equipment. A novelty of this project will be to develop and optimize a free-falling instrument that can rest remotely on the seabed and collect bottom water and particulate samples across a 10 to 100 meter thick layer of the ocean using remote and autonomous controls. The instrument will be developed with support from the Ocean Technology and Engineering Group at the National Oceanography Centre, with additional funds from the Royal Society provided by Prof. Gideon Henderson at the University of Oxford. The new instrument will be first used in conjunction with the NERC Shelf Sea Biogeochemistry Programme in the UK North Atlantic planned for late 2014. Observed conditions will be simulated in laboratory experiments to identify chemical exchange mechanisms between sediments and seawater. The fellowship will benefit from analytical expertise at the Marine Trace Element Laboratory of University of South Carolina, USA, through which newly developed metal isotope observations in seawater will be made. Future deployments of the new instrument are planned within the lifetime of this fellowship through interaction with the international GEOTRACES program. A legacy of this work will be to refine estimates of micronutrient supply from ocean margins to improve ocean climate models, and to establish an operational platform for a broad range of chemical observations across an under-explored part of the Earth system. Potential research avenues for the future include refining chemical tracers of ocean processes; monitoring marine habitats and contaminant transport processes; and observing chemical processes at the seafloor in dynamic ice-covered or volcanic regions of the ocean over time.