HR: 0800h
AN: B21A-1023    [Abstracts]
TI: Petroleum Weathering Associated with Hydrocarbon Migration and Seepage, a Case Study From the Santa Barbara Channel, CA.
AU: * Wardlaw, G D
EM: gwardlaw@umail.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, 1006 Webb Hall, Santa Barbara, CA 93106-9630 United States
AU: Nelson, R K
EM: rnelson@whoi.edu
AF: Woods Hole Oceanographic Institution, Marine Chemistry and Geochemistry Department, MS #4, Woods Hole, MA 02543 United States
AU: Reddy, C M
EM: creddy@whoi.edu
AF: Woods Hole Oceanographic Institution, Marine Chemistry and Geochemistry Department, MS #4, Woods Hole, MA 02543 United States
AU: Valentine, D L
EM: valentine@geol.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, 1006 Webb Hall, Santa Barbara, CA 93106-9630 United States
AB: A 2003 report by the National Research Council estimates that 50 to 70 percent of oil that is released into the sea is from natural seeps (National Research Council, 2003), indicating that catastrophic oil spills or the runoff from roads and highways are not the major sources of oil in the marine environment. For example, approximately 37 tons of petroleum is emitted daily from seeps off the coast of Santa Barbara, California (Quigley et al. 1996). The Santa Barbara seeps are some of the most active in the world and have been releasing petroleum for thousands of years. Sheens of oil on the water surface and tar patches on the beaches are ubiquitous along the coastline of Santa Barbara and are continuing reminders of this natural process. Although the geochemistry of these seeps have been studied in the past, it has been hindered by the complexity of the petroleum hydrocarbons and the inability of traditional gas chromatography to separate, identify, and quantify each component of the oil. To expand on these previous efforts, we have begun to use comprehensive two-dimensional gas chromatography (GCxGC). This new technology provides at least an order of magnitude increase in the resolution and detection of petroleum hydrocarbons compared to traditional methods. Preliminary work using GCxGC has focused on examining the chemical composition of unrefined petroleum as it migrates up from depth through natural faults to the seafloor, from the seafloor to the sea surface, and from the sea surface to local beaches. Petroleum collected from a subsurface reservoir (Platform Holly Well 2342-15) is composed of a wide range of resolved petroleum hydrocarbons including n-alkanes, branched alkanes, cycloalkanes, linear alkane benzenes, polycyclic aromatic hydrocarbons, steranes, hopanes, cyclic isoprenoids, and very large branched biomarkers with 38 to 40 carbons. This product is significantly different than oil emerging from the seafloor at the Jackpot seep, which we believe is due to biodegradation. Alternatively, direct comparisons of the latter to samples collected on the sea surface show extensive losses of light-end components due to evaporation and not water washing. Tar balls collected from nearby beaches appear to be the end result of biodegradation, evaporation, and water washing of the original material seeping from the ocean floor. These initial studies reveal that the geochemistry and processes acting on petroleum seeping from the ocean floor are complex. Efforts are underway to construct accurate models that will quantify each environmental process that affects the fate of petroleum in the marine environment.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 4251 Marine pollution (0345, 0478)
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4850 Marine organic chemistry (0470, 1050)
SC: Biogeosciences [B]
MN: Fall Meeting 2005