SGER: Mobilization and Deposition of Organic Matter along the Louisiana Coast following Hurricane Katrina

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ABSTRACTOCE-0553090Hurricanes and large storms play a critical but often unpredictable role in the transport and redistribution of sediments and organic matter in the coastal ocean. Previous work on the effects of Hurricane Lili, a much smaller storm than Hurricane Katrina, revealed large seaward transport and deposition of fine sediments onto the shelf region west of the storm track. Furthermore, massive deposition of organic carbon and nitrogen associated with these fine sediments was observed throughout the region, vastly exceeding the long-term accumulation of these materials in this area. Based on earlier findings following Hurricane Lili and given its much larger magnitude and intensity, Hurricane Katrina (~ 4m storm surge, 135-160 mph winds) may have potentially mobilized and redistributed much larger amounts of sediment and associated organic matter over a much wider area. The majority of the offshore transport likely occurred in the western region of the storm track, where winds were predominantly in the offshore direction. The impacted area ranges from the more distal Atchafalaya River subaqueous delta to the more proximal Mississippi River delta and associated canyon. With funding from this Small Grant for Exploratory Research, investigators at the Oregon State University will collect samples and carry out analyses of seabed sediments from the region affected by Hurricane Katrina to evaluate its effects on the mobilization and deposition of sediment and organic matter along the Louisiana Shelf. The immediacy of the proposed work is to sample the storm deposits before they are eroded and mixed and while they retain their unique chemical (e.g. short-lived isotopes, organic carbon contents) characteristics. In cooperation with colleagues at East Carolina University and Tulane University, he research team will sample the seabed at several locations along the Louisiana Shelf that have been previously sampled and for which the sediment accumulation rates and sedimentary organic matter have been characterized. These observations will provide baseline information that will be compared to the findings from samples collected after the Katrina event. The Oregon State group will analyze the sediments collected at these sites to determine the concentration and composition of organic matter in the storm layer. The chemical analyses of the organic matter (e.g. stable isotopes, radiocarbon concentrations, terrigenous and marine biomarkers) will help characterize the sources of the organic matter, which will yield information on the ultimate source of the mobilized materials. These results will yield novel insights into the effects of such large storms on the sedimentology and biogeochemistry of this region. Specifically, it will provide detailed information on the role of large storms as a mechanism for the export of terrigenous materials from the inshore regions of the shelf to the more offshore regions, such as the Mississippi Canyon and the prograding Atchafalaya subaqueous-delta clinoform.The broader impacts of the proposed work include the collection and analyses of seabed samples impacted by a major hurricane in a coastal system that has a well-developed baseline of information. Collaboration with other research groups will enhance the understanding of sediment and organic matter cycling in coastal systems during such stochastic events. The proposal will also include involvement by undergraduate students in the field and laboratory aspects of the work.