title: Pathways of organic carbon oxidation in three continental margin sediments.
abstract: We have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of Denmark and Norway. Rates of NH4+ and Sigma CO2 liberation sediment incubations were used with O2 penetration depths to conclude that O2 respiration accounted for only between 3.6-17.4% of the total organic carbon oxidation. Dentrification was limited to a narrow zone just below the depth of O2 penetration, and was not a major carbon oxidation pathway. The processes of Fe reduction, Mn reduction and sulfate reduction dominated organic carbon mineralization, but their relative significance varied depending on the sediment. Where high concentrations of Mn-oxide were found (3-4 wt% Mn), only Mn reduction occurred. With lower Mn oxide concentrations more typical of coastal sediments, Fe reduction and sulfate reduction were most important and of a similar magnitude. Overall, most of the measured O2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon. We suspect that the importance of O2 respiration in many coastal sediments has been overestimated, whereas metal oxide reduction (both Fe and Mn reduction) has probably been well underestimated.
authors.affiliation: Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta 30332-0340, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Canfield
authors.forename: B B
authors.initials: BB
authors.lastname: Jorgensen
authors.forename: H
authors.initials: H
authors.lastname: Fossing
authors.forename: R
authors.initials: R
authors.lastname: Glud
authors.forename: J
authors.initials: J
authors.lastname: Gundersen
authors.forename: N B
authors.initials: NB
authors.lastname: Ramsing
authors.forename: B
authors.initials: B
authors.lastname: Thamdrup
authors.forename: J W
authors.initials: JW
authors.lastname: Hansen
authors.forename: L P
authors.initials: LP
authors.lastname: Nielsen
authors.forename: P O
authors.initials: PO
authors.lastname: Hall
mesh_terms: D002244:Carbon / Q000737:chemistry / Q000378:metabolism*; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism; D003718:Denmark; D019015:Geologic Sediments / Q000032:analysis* / Q000382:microbiology; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D008386:Marine Biology; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism; D009664:Norway; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism; D014871:Water Microbiology
chemical_list: D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D013431:Sulfates; D002245:Carbon Dioxide; D008345:Manganese; D002244:Carbon; D007501:Iron; D010100:Oxygen