Controls on the distribution and accumulation of anic matter in sediments from the Mississippi and Atchafalaya river margin.pdf

Marine Chemistry 92 (2004) 331–352
ate/marchem
Controls on the distribution and accumulation of terrigenous
organic matter in sediments from the Mississippi
and Atchafalaya river margin
Elizabeth S. Gordon*, Miguel A. Gon˜i
Department of Geological Sciences and Marine Science Program, University of South Carolina, Columbia, SC 29208, United States
Received 21 November 2003; received in revised form 8 April 2004; accepted 30 June 2004
Abstract
Sediment samples from 14 box cores across the Mississippi and Atchafalaya River Margin were examined in order to
quantify the magnitude position of the OM depositional flux in sediments from a river-dominated margin and
identify the fate of terrigenous OM in the study area. Elemental, isotopic, mineral surface area, and terrigenous biomarker
analyses suggest that physical sorting of particles across this river-dominated margin controls the position of
sedimentary OM. Sediment accumulation rates in the area ranged from to cm/year and showed an inverse
logarithmic relationship with water depth. anic carbon (OC) content (–%) was observed on the inner shelf
(b10 m water depth) and slope (N200 m water depth), with lower OC (%) measured on the outer shelf (10–200 m water
depth). Mineral surface area (SA) showed a similar spatial distribution as OC, with the highest values on the inner shelf
(average 41 m2/g) and slope (average 54 m2/g), and low SA values (average 23 m2/g) on the outer shelf. Association of OM
with minerals and its apparent differential transport across the study area results in the greatest proportion of OM
accumulating on the inner shelf (37%), although the slope also plays a significant role in OM accumulation (33%) due to its
greater areal extent.
13
anic carbon isotope (d COC) values ranged between À23x and À21x across the study area, with a slight
seaward enrichment. The spatial trend in lignin yields mirrored that of d13C, with a substantial decrease in ligni