HR: 17:00h
AN: OS42C-05    [PDF]
TI: Expulsion of Barium and Methane at Mud Volcanoes in the Gulf of Mexico
AU: * Castellini, D G
EM: dgc@rice.edu
AF: Rice University, Earth Science - MS126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Dickens, G R
EM: jerry@rice.edu
AF: Rice University, Earth Science - MS126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Snyder, G T
EM: gsnyder@rice.edu
AF: Rice University, Earth Science - MS126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Gilhooly, W P
EM: wpg6n@virginia.edu
AF: University of Virginia, Department of Envirnmental Science 291 McCormick Rd. P.O. Box 400123, Charlottesville, VA 22904-4123 United States
AU: Ruppel, C D
EM: cdr@piedmont.eas.gatech.edy
AF: Georgia Institute of Technology, School of Eart & Atmospheric Scienes 311 Ferst Dr., Atlanta, GA 30332-0340 United States
AB: Submarine mud volcanoes and cold-seeps along continental margins transfer methane from gas-charged marine sediments to the water column. Such methane venting is dynamic and may provide an important and variable supply of carbon to the ocean and atmosphere through time. Barite mounds and chimneys have been found around some modern mud volcanoes and seeps, and similar structures can be identified in the geological record (e.g., bedded barite deposits). These observations suggest that expelled methane-rich fluids are greatly enriched in dissolved barium. However, there are very few analyses of barium concentrations in these systems. Here, we examine the dissolved barium of pore fluids from a series of shallow piston cores across two submarine mud volcanoes in the Gulf of Mexico. Dissolved barium concentrations at 1.5 m below the seafloor at the Garden Bank volcano range from 18200 $\mu$M at the center of the feature to 0.56 $\mu$M on its flanks approximately 1 km away. Similarly, dissolved barium concentrations at the Mississippi Canyon volcano range from 15600 $\mu$M to 0.50 $\mu$M. Thus, the concentrations in the cores of the mud volcanoes are nominally 5 orders of magnitude greater than in mean ocean water ($\sim$0.1 $\mu$M). Anaerobic oxidation of upward flowing methane consumes sulfate, which leads to the dissolution of barite and release of barium to pore fluids. Because this mechanism alone cannot explain the extreme concentrations in the mud volcanoes, a deep source of barium may exist in the Gulf of Mexico strata. Our current work is focused on quantifying the fluxes and sedimentary fate of expelled barium at these locations. However, even if a large fraction of the barium precipitates adjacent to the sites of methane venting, fluid expulsion at mud volcanoes must significantly impact the barium cycle in the Gulf of Mexico. Conceivably, submarine mud volcanoes and cold-seeps along continental margins are a major source of barium to the deep ocean, a concept that has profound implications with respect to certain paleoceanographic reconstructions.
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4825 Geochemistry
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting