Deep Sediment-Sourced Methane Contribution to Shallow Sediment Organic Carbon: Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico

Richard B. Coffin, Christopher L. Osburn, Rebecca E. Plummer, Joseph P. Smith, Paula S. Rose and Kenneth S. Grabowski
Additional contact information
Richard B. Coffin: Naval Research Laboratory, Washington, DC 20735, USA
Christopher L. Osburn: Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, USA
Rebecca E. Plummer: Department of Geology, University of Maryland, College Park, MD 20742, USA
Joseph P. Smith: Oceanography Department, US Naval Academy, Annapolis, MD 21402, USA
Paula S. Rose: Naval Research Laboratory, Washington, DC 20735, USA
Kenneth S. Grabowski: Naval Research Laboratory, Washington, DC 20735, USA

Energies, 2015, vol. 8, issue 3, 1-23

Abstract: Coastal methane hydrate deposits are globally abundant. There is a need to understand the deep sediment sourced methane energy contribution to shallow sediment carbon relative to terrestrial sources and phytoplankton. Shallow sediment and porewater samples were collected from Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico near a seafloor mound feature identified in geophysical surveys as an elevated bottom seismic reflection. Geochemical data revealed off-mound methane diffusion and active fluid advection on-mound. Gas composition (average methane/ethane ratio ~11,000) and isotope ratios of methane on the mound (average ? 13 C CH4(g) = ?71.2‰; D 14 C CH4(g) = ?961‰) indicate a deep sediment, microbial source. Depleted sediment organic carbon values on mound (? 13 C SOC = ?25.8‰; D 14 C SOC = ?930‰) relative to off-mound (? 13 C SOC = ?22.5‰; D 14 C SOC = ?629‰) suggest deep sourced ancient carbon is incorporated into shallow sediment organic matter. Porewater and sediment data indicate inorganic carbon fixed during anaerobic oxidation of methane is a dominant contributor to on-mound shallow sediment organic carbon cycling. A simple stable carbon isotope mass balance suggests carbon fixation of dissolved inorganic carbon (DIC) associated with anaerobic oxidation of hydrate-sourced CH 4 contributes up to 85% of shallow sediment organic carbon.

Keywords: methane; advection; geochemistry; carbon isotopes; sediment carbon (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2015
References: View references in EconPapers View complete reference list from CitEc
Citations:

Downloads: (external link)
https://www.mdpi.com/1996-1073/8/3/1561/pdf (application/pdf)
https://www.mdpi.com/1996-1073/8/3/1561/ (text/html)

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:gam:jeners:v:8:y:2015:i:3:p:1561-1583:d:46072

Access Statistics for this article

Energies is currently edited by Ms. Agatha Cao

More articles in Energies from MDPI
Bibliographic data for series maintained by MDPI Indexing Manager ().