HR: 14:15h
AN: H23C-04 INVITED     [Abstracts]
TI: New Insights into the Biogeochemistry of Particulates in the Lower Mississippi River and Adjacent Margin: Transport and Transformation Processes
AU: * McKee, B A
EM: bmckee@tulane.edu
AF: Department of Earth and Environmental Sciences, Center for River-Ocean Studies (CeROS), Tulane University, New Orleans, LA 70118 United States
AB: During the past few years, a number of research projects in the lower Mississippi River and on the adjacent margin have greatly increased our understanding of biogeochemical cycling in this major river system. In particular, we have gained a better appreciation for the dynamic nature of large river systems and the importance of processes that operate on time scales of minutes to days and on space scales of centimeters to decimeters. An overview of these new insights will be presented, which represents the work of many colleagues and students over the past 5 years. These include: (1) our current assessment of the geochemical characteristics and flux of suspended materials within the lower Mississippi; (2) an evaluation of the seasonal storage, diagenetic transformation and remobilization of particulates within the lower Mississippi; (3) recent work quantifying the deposition of particulate materials on the adjacent margin; and (4) initial assessment of the fate (burial or export) of particulate materials in the coastal margin. Gram-quantity suspended particulate samples have been collected (1-3 times per month) over the past two years at a station in the lower river. Analyses of geochemical tracers (⁷Be, ²³⁴Th, ¹³⁷Cs, ²¹⁰Pb, ^234/238U) reveal a large seasonal variability in particulate source and residence time within the basin, including remobilization of older stored sediments. Within the lower 500 km of the Mississippi, riverine suspended sediments are deposited on the riverbed during decelerating flows and can remain there for 3-20 months, depending on the annual hydrograph. Substantial diagenetic alteration occurs during these periods of seasonal storage, thereby impacting the characteristics and partitioning of materials that enter the coastal zone. Riverine particulates are delivered to the adjacent shelf as a diffuse suspended sediment plume and as a highly concentrated near-bottom suspension (fluid mud). Extensive remineralization and reususpension/export takes place within margin sediments after deposition. As a result, less than half of the organic carbon delivered to the shelf is buried there on a decadal time scale.
UR: http://www.tulane.edu/~riomar
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1655 Water cycles (1836)
DE: 1815 Erosion and sedimentation
DE: 1860 Runoff and streamflow
DE: 4558 Sediment transport
SC: Hydrology [H]
MN: 2005 Joint Assembly