HR: 1330h
AN: OS23A-15    [Abstracts]
TI: Sources and Transformations of Organic Matter in Surface Sediments Across Different Dispersal Pathways on the Louisiana Continental Shelf/Slope: The Application of Plant Pigments and Lignin-Phenols as Biomarkers
AU: * Sampere, T
EM: tsampere@tulane.edu
AF: Tulane University, Tulane University, Department of Earth and Environmental Sciences, New Orleans, LA 70118
AU: Bianchi, T S
EM: tbianch@tulane.edu
AF: Tulane University, Tulane University, Department of Earth and Environmental Sciences, New Orleans, LA 70118
AB: Bulk surface sediments from the Mississippi Margin were analyzed for lignin phenols (a biomarker of vascular plant material) and plant pigment biomarkers. Sediment samples were collected at five stations along a transect extending from the mouth of the Mississippi River (SW pass) to the Mississippi River Canyon (MRC)and a second transect from outside SW Pass extending to Barataria Bay, along-shelf at the 50 meter isobath. An additional smaller transect comprised of three stations from just inside Barataria Bay to the inner shelf was also sampled. The average lambda-8 (e.g., lignin-phenols normalized to 100 mg carbon) and (Ad/Al)v (e.g., decayed lignin) values for all shelf stations was 1.12 ug/100g OC and 0.49, respectively. On the cross-margin transect, lamda-8 and Ad/Al)v values ranged from 1.45 to 0.34 and 0.35-0.78, respectively, and from 1.05 to 0.42 and 0.45-0.68 along the 50 m isobath transect, respectively. The Barataria Bay transect showed higher lambda-8 values compared to mid and outer-shelf sites and ranged from 0.93 to 4.85. Terrestrially-derived organic matter (TOM) (based on lignin-phenol concentrations) showed similar trends of decreasing concentrations and increasing degradation in surface sediments along both major transects: 1) across shelf to the MRC and 2) westward along the 50 m isobath. Similar decreases in lignin abundance and increased degradative state of TOM along either major transport pathways indicate that decomposition of TOM in mobile muds in shallow waters and/or across deeper waters to the MRC are effective at oxidizing terrestrial material, yet over different time periods. Lignin-phenols also indicated fresh loading of local marsh material from Barataria Bay to the inner shelf, emphasizing that local marshes are sources of TOM the the coast. Pigment data indicated much of the marine-derived organic matter (MDOM) is dominated by diatoms. Increasing pigment concentrations along the 50 m isobath transect co-occurred with decreasing lignin concentrations suggesting local sources of phytoplankton inputs outside the Mississippi River plume. The occurrence of fresh diatom pigments in the MRC may suggest transport of MDOM from the shelf to the MRC. Lignin data will also be contrasted between pre- and -post hurricane Ivan concentrations as a major disturbance event.
DE: 3344 Paleoclimatology
DE: 4215 Climate and interannual variability (3309)
DE: 4219 Continental shelf processes
DE: 4532 General circulation
DE: 4815 Ecosystems, structure and dynamics
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly