HR: 10:35h
AN: OS22A-02    [Abstracts]
TI: Sources of Organic Carbon to a River-Dominated Coastal Shelf: the Use of Biomarkers to Track Terrestrial Organic Matter Inputs
AU: * Wysocki, L A
EM: lwysock@tulane.edu
AF: Tulane University, Department of Earth and Environmental Sciences, New Orleans, LA 70118, United States
AU: Bianchi, T S
EM: tbianchi@tamu.edu
AF: Texas A&M University, Department of Oceanography, College Station, TX 77843, United States
AU: Filley, T R
EM: filley@purdue.edu
AF: Purdue University, Department of Earth and Atmospheric Sciences, West Lafayette, IN 47907, United States
AB: Because of high sedimentation rates in the coastal ocean, particularly along river-dominated ocean margins, estuarine and coastal sediments can be important repositories for organic carbon derived from both allochthonous and autochthonous sources. Using molecular biomarker analyses (C:N, bulk isotopes, lignin, and compound-specific isotopes) this study examines the sources of organic carbon to the Louisiana shelf within the dispersive path of the Mississippi River. Surface sediment samples were collected from a grid of stations across the Mississippi river plume and adjacent waters during two cruises in the spring and fall of 2000. Lignin biomarker data shows a mixture of sources to the sediments. Sediments near the mouth of the Mississippi River are chemically distinct from those found in the central portion of the shelf. Based on lignin acid:aldehyde ratios and stable C isotope analyses, terrestrial material delivered in this region is comparatively less degraded and richer in C4 plant carbon. A mixing model based on parameters defining riverine, marsh, and marine organic carbon suggests the highest OC inputs to the shelf in spring were from marine sources (58% to 63% marine OC) while the river supplied the most OC (63% to 76% river OC) during the fall sampling period. This model furthermore estimated marsh inputs ranging from 20% to 30% of the OC in spring and 13% to 19% during the fall, in contrast to the prevailing notion that local terrestrial sources provide insignificant inputs to the carbon pool in this environment.
DE: 0428 Carbon cycling (4806)
DE: 0442 Estuarine and nearshore processes (4235)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly