GEOTRACES GP-17 OCE: Measurement of 7Be as a Tracer of Upper Ocean Processes

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The International GEOTRACES Program was established to identify processes and quantify fluxes that control the distributions of key trace elements and their isotopes in the ocean as these chemical species play important roles as nutrients, as tracers of current and past oceanographic processes, and as contaminants derived from human activity. This is a proposal to make measurements of one such species (the radioactive isotope Beryllium-7) in the water column and on aerosols during the US GEOTRACES GP17-OCE section of the South Pacific and Southern Oceans. Beryllium-7 is a tracer that, because of its half-life (53.3 days), allows the study of processes such as biological production, nutrient regeneration, and atmospheric deposition, which occur over seasonal time scales and shallow depths (200m). The data will be used to derive important biogeochemical rate information pertinent to interpreting sources and transformations of the extensive suite of trace elements and isotopes that will be measured during the expedition. The proposed work will measure beryllium-7 in the surface waters and in the lower atmosphere to provide estimates of the atmospheric input of relevant trace elements and isotopes. The atmospheric input into the global ocean is an important budgetary component of numerous chemical species, but there is little-to-no data from this region. Determination of the atmospheric input and its variability will allow observation of the oceanic response to this flux along the cruise track. The water column measurements of beryllium-7 will be used as a tracer of physical processes, such as mixing and upwelling, which redistribute biologically active species. The rate of oxygen utilization (OUR) within the upper thermocline will also be determined by water column measurements of beryllium-7 coupled with hydrographic data and observed oxygen distributions. Accurate characterization of this process within 200m of the euphotic zone, where carbon utilization is most intense, has been difficult owing to limitations of other available techniques which are characterized by multiyear to decadal timescales that likely miss the rapid organic matter remineralization occurring along shallow isopycnal surfaces. The seasonal timescale of beryllium-7 will allow for estimation of OUR within the shallow water just beneath the euphotic zone, where the most significant remineralization occurs. This research will support undergraduate researchers in a minority serving institution.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.