HR: 1340h
AN: OS43A-0538    [Abstracts]
TI: Does Barite Form in the Oceanic Water Column?
AU: * Rushdi, A
EM: arushdi@coas.oregonstate.edu
AF: COAS, Oregon State University, Corvallis, OR 97331 United States
AU: Collier, R
EM: rcollier@coas.oregonstate.edu
AF: COAS, Oregon State University, Corvallis, OR 97331 United States
AB: Understanding the physical and chemical conditions that lead to the formation and preservation of barite in marine environment is important to validate the application of barium/barite abundance in ocean sediments as an index of productivity. In this work we rely on time-series sediment trap results to explore: (1) barium and strontium concentration variations; (2) the changes in the degree of saturations with respect to barite and celestite; and (3) the equilibrium relationship between barite and celestite in seawater cup solutions in order to investigate the formation of "natural" marine barite as the mixed solid phase Ba$_{x}$Sr$_{1-x}$SO$_{4}$. The data were collected along 170W between Subtropical Front and Ross Sea from November 1996 to January 1997, as part of the U.S. Joint Global Ocean Flux Study (USJGOFS-AESOPS) to study the Southern Ocean impact on biogeochemical processes of the oceans. High concentrations of barium and strontium were measured in the cup solutions of sediment traps during the high particle flux periods. The cup solutions of the sediment traps were estimated to be supersaturated with respect to pure barite between 100% and over 900%. They were undersaturated to slightly supersaturated with respect to celestite, ranging between 14 and 150%. The modeled equilibrium relationship of a mixed solid phase of barite and celestite in solution has indicated that barite with up to 23% mole fraction of SrSO$_{4(s)}$ might form in these cup solutions. The Sr/Ba ratios in the bulk solid phases collected from the same sediment trap cups were much higher (25-99%) than modeled values and are likely controlled by non-sulphate solids. These results also suggest that the precipitation of marine barite crystals is not favorable in these cup solutions due to the high solubility of high strontian barite. If the cup solutions can approximate the isolated chemical environment within particle aggregates collected by these traps, then it is unlikely that significant precipitation of marine barite occurs during their transport to the seafloor.
DE: 4805 Biogeochemical cycles (1615)
DE: 4807 Chemical speciation and complexation
DE: 4825 Geochemistry
DE: 1050 Marine geochemistry (4835, 4850)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting