Fate and transport of sedimentary organic carbon on the Louisiana continental margin
Description
Lignin and pigment biomarkers were analyzed in sediments of the Louisiana Continental margin along two major depositional pathways (along shore and offshore to the Mississippi Canyon) from SW Pass in July 2003. Results from surface sediments indicate resuspension and reworking of shelf sediments in shallow waters and mobile mud deposits were more effective at oxidizing terrestrial material west of SW Pass than to the southwest. Barataria Bay material may be a contributing source of sedimentary organic matter in shallow shelf areas bordering the Bay and is thus potentially important in carbon cycling. Hurricane Ivan mobilized sedimentary organic carbon (SOC) offshore and homogenized terrestrial sediment parameters and gradients Results from box-core profiles showed preferential loss of more labile pigment SOC during burial and diagenesis. Low burial efficiencies along the western transect for bulk and labile biomarkers indicate mobile muds were efficient in the remineralization of labile organic matter. Lignin appeared to be a useful paleo indicator in dynamic RioMar environments likely reflecting source input rather than diagenesis after initial deposition. Pigment concentrations and ratios may not be useful in a quantitative sense for paleo-reconstructions within dynamic RioMar regions. Oxic degradation of labile material in the Surface Active Zone was highly efficient, effecting the quantity and quality of material buried below Lignin profiles in age-dated cores (210Pb geochronology) indicate artificial reservoir retention as a major control on organic carbon quantity and quality post-1950 reaching the margin, whereas, pre-1950 sediments may reflect soil erosion due to land-clearing and farming practices. Terrestrially derived organic carbon signatures were mixed angiosperms over the last 150 yrs. Stochastic events such as hurricanes and large river floods have a measurable, albeit ephemeral, effect on the shelf SOC record. Land-use changes in the MR basin have likely affected carbon cycling and SOC burial on the LCM over a large spatial extent as observed by similar trends in cores from across and along margin. Finally, sediment focusing seems to be a very important aspect that can complicate down-core interpretation when trying to make comparisons over wide spatial scale