Osmium Isotopes in Seawater

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The work to date on the marine geochemistry of osmium points to the need to constrain the Os-isotopic composition of the oceans in order to derive cosmic and terrestrial Os fluxes from the more readily conducted measurements on sediments and Mn-nodules. The Os-isotopic composition of the oceans cannot be properly assessed without at least a first order understanding of the oceanographic behavior of the element. This research will elucidate the marine chemistry of Os through determination of its distribution and isotopic composition in seawater. Together with a separate but compatible study of marine solid phases, the project will significantly increase our overall comprehension of the marine geochemical cycle of this element. Such groundwork is prerequisite to exploiting the potential of this isotopic system for probing marine geochemical processes. Whether the Os-isotopic system in seawater is homogeneous will determine if its sedimentary signature records the relative magnitudes of its crustal, mantle and cosmogenic sources on the global scale or if it traces more local processes affecting its accumulation. This in turn determines whether the paleo cosmogenic material flux or the paleo-redox state of the oceans might be reconstructed from sedimentary records of Os. On a more immediate timescale, an understanding of the behavior of Os in the water column will provide the basis for using anthropogenic Os as a tracer in affected coastal areas and enclosed basins.