HR: 1340h
AN: OS13A-0516    [Abstracts]
TI: Nature of Decadal-scale Sediment Accumulation in the Mississippi River Deltaic Region
AU: * Corbett, R
EM: corbettd@mail.ecu.edu
AF: East Carolina University, Department of Geology Coastal Resources Management, Greenville, NC 27858 United States
AU: McKee, B
EM: bmckee@tulane.edu
AF: Tulane University, Deptartment of Earth and Environmental Sciences, New Orleans, LA 70118 United States
AU: Allison, M
EM: malliso@tulane.edu
AF: Tulane University, Deptartment of Earth and Environmental Sciences, New Orleans, LA 70118 United States
AB: Rivers deliver approximately 15 x 10$^{9}$ tons of sediment to coastal margins each year. This sediment delivery to coastal systems plays a key role in the global carbon and nutrient cycles as deltas and continental shelves are considered to be the main repositories of organic matter in marine sediments. The Mississippi River, delivering more than 50% of the total dissolved and suspended materials from the conterminous U.S., is the dominant stimulus for coastal processes in the northern Gulf of Mexico. Draining approximately 47% of the conterminous U.S., the Mississippi delivers approximately 2 X 10$^{8}$ tons of suspended matter to the northern Gulf shelf each year. Although many researchers have evaluated sediment accumulation in different areas on the shelf near the Mississippi River Delta, this study examines data from more than 90 cores collected throughout the last decade covering majority of the shelf ($<$150 m water depth) adjacent to the Mississippi River Delta. This provides a unique and invaluable dataset of the spatial and modern temporal variations of the sediment accumulation in this dynamic coastal environment. Four types of $^{210}$Pb profiles were observed from these short cores (15-45 cm) collected on the shelf. Proximal to Southwest Pass in 30-100 m of water, two types of non-steady state profiles were observed. These profiles either showed (1) rapid accumulation or (2) an event layer with a change in sedimentation rate. Sedimentation rates in this area are typically $>$2.5 cm yr$^{-1}$ ($>$1.6 g cm$^{-2}$ y$^{-1}$). Two Kasten cores ($\sim$200 cm in length) collected near Southwest Pass also indicate rapid deposition ($>$4 cm y$^{-1}$) on a longer timescale than that captured in the box cores. Near shore ($<$20 m), profiles are dominated by (3) mixing, probably reworked by waves and currents, with the exception of an area just south of Barataria Bay that have steady state profiles. The remainder of the shelf (distal of Southwest Pass) is dominated by (4) steady state accumulation beneath a $\sim$10 cm mixed layer. Sedimentation rates for the distal shelf are typically $<$0.7 cm yr$^{-1}$ ($<$0.4 g cm$^{-2}$ y$^{-1}$). A preliminary sediment budget indicates that more than 50% of the sediment delivered by the river annually are either deposited prior to exiting Southwest Pass or is transported out of the study area, presumably off the shelf.
DE: 4804 Benthic processes/benthos
DE: 4860 Radioactivity and radioisotopes
DE: 4863 Sedimentation
DE: 4219 Continental shelf processes
DE: 3022 Marine sediments--processes and transport
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting