Barite in the Central Equatorial Pacific: Implications for Marine Chemistry, Productivity, and Circulation of the Modern and Past Oceans

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The mineral barite BaSO4) is an ubiquitous component of particulate material in the water column, and of pelagic sediments. Many workers have noted a correlation between the abundance of barite in sediments and productivity in overlying surface waters. Barite is clearly important in the geochemical cycle of Ba, and it is also quite insoluble and therefore resists dissolution and diagenetic exchange in sediments. Furthermore, three elements for which the seawater isotopic composition is important for solving many paleoceanographic problems (Sr, S and Nd) occur in barite in amounts that permit precise isotopic measurements to be made on very small amounts of the separated phase. For all of these reasons, barite appears to be an important tracer of productivity, geochemical cycling, and a host of processes that may affect seawater chemical and isotopic compositions, e.g. climate, tectonics, sealevel change and rates of marine hydrothermal activity. Nevertheless, the present understanding of the sites and mechanisms of barite formation, transport, and fate in the sedimentary column is very incomplete and the linkage between Ba, barite and C fluxes need to be clarified. In this research a mass- balance, morphological, geochemical and isotopic approach to the study of the cycling of barite in upper sedimentary layers of the equatorial Pacific and its relation to the C cycling will be made Novel aspects of the work include the use of Nd, Sr and S isotopes as clues to the environment of formation and possible recycling of barite. This study will make use of sediment trap, filtered and bottom sediment samples, and will be closely coordinated with geochemical and isotopic investigations of the water column by other workers. It will also be undertaken with close attention to the potential of barite as a contemporary as well as a paleo monitor of biogeochemical and isotopic characteristics of seawater.