Marine Geochemistry of Lithium Isotopes

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A new method has been developed for the measurement of lithium isotope ratios in geological material, as a result of an initial study funded by NSF. The mass spectrometric technique involves the thermal ionization of lithium tetraborate and is capable of producing 6Li/7Li ratios with an uncertainty of 1.3 0/00 (one standard deviation). The results of a preliminary survey indicate important variation of th eisotope composition of Li in the marine environment and demonstrate the usefulness of Li isotope ratio as a tracer for mass exchange in the ocean. This proposal summarizes the findings of the initial research and requests support for a comprehensive investigation of the marine isotope geochemistry of lithium. Efforts will be directed at determining the isotopic composition of the sources and sinks of Li in the ocean and the isotopic fractionation associated with the mass transfer processes. The main emphasis is on the utilization of Li isotope systematics in the understanding of (1) the control on the Li isotopic composition of seawater, (2) the direction and magnitude of Li transfer during seawater-basalt interaction and (3) the process by which Li is enriched in marine sediments. These considerations address the problem of mass balance of Li in the ocean and is of fundamental importance in the characterization of the geochemical cycle of Li.