Coupled organic and inorganic carbon cycling in the deep subseafloor sediment of the northeastern Bering Sea Slope (IODP Exp. 323)

We studied microbially mediated diagenetic processes driven by carbon mineralization in subseafloor sediment of the northeastern Bering Sea Slope to a depth of 745 meters below seafloor (mbsf). Sites U1343, U1344 and U1345 were drilled during Integrated Ocean Drilling Program (IODP) Expedition 323 a...

Full description

Saved in:
Bibliographic Details
Published in:Chemical geology 2011-05, Vol.284 (3), p.251-261
Main Authors: Wehrmann, Laura M., Risgaard-Petersen, Nils, Schrum, Heather N., Walsh, Emily A., Huh, Youngsook, Ikehara, Minoru, Pierre, Catherine, D'Hondt, Steven, Ferdelman, Timothy G., Ravelo, Ana Christina, Takahashi, Kozo, Zarikian, Carlos Alvarez
Format: Article
Language:English
Subjects:
Bering Sea
Carbon
Carbonates
Deep subseafloor sediment
Diagenetic carbonate formation
Integrated Ocean Drilling Program
Magnesium
Methane
Microbially mediated diagenetic processes
Microorganisms
Mineralization
Organic carbon mineralization
Sediments
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:We studied microbially mediated diagenetic processes driven by carbon mineralization in subseafloor sediment of the northeastern Bering Sea Slope to a depth of 745 meters below seafloor (mbsf). Sites U1343, U1344 and U1345 were drilled during Integrated Ocean Drilling Program (IODP) Expedition 323 at water depths of 1008 to 3172 m. They are situated in the high productivity “Green Belt” region, with organic carbon burial rates typical of the high-productivity upwelling domains on western continental margins. The three sites show strong geochemical similarities. The downward sequence of microbially mediated processes in the sediment encompasses (1) organoclastic sulfate reduction, (2) anaerobic oxidation of methane (AOM) coupled to sulfate reduction, and (3) methanogenesis. The sediment contains two distinct zones of diagenetic carbonate formation, located at the sulfate–methane transition zone (SMTZ) and between 300 and 400 mbsf. The SMTZ at the three sites is located between 6 and 9 mbsf. The upward methane fluxes into the SMTZ are similar to fluxes in SMTZs underlying high-productivity surface waters off Chile and Namibia. Our Bering Sea results show that intense organic carbon mineralization drives high ammonium and dissolved inorganic carbon (DIC) production rates (> 4.2 mmol m − 3 y − 1 ) in the uppermost 10 mbsf and strongly imprints on the stable carbon isotope composition of DIC, driving it to a minimum value of − 27‰ (VPDB) at the SMTZ. Pore-water calcium and magnesium profiles demonstrate formation of diagenetic Mg-rich calcite in the SMTZ. Below the SMTZ, methanogenesis results in 13C-enrichment of pore-water DIC, with a maximum value of + 11.9‰. The imprint of methanogenesis on the DIC carbon isotope composition is evident down to a depth of 150 mbsf. Below this depth, slow or absent microbially mediated carbon mineralization leaves DIC isotope composition unaffected. Ongoing carbonate formation between 300 and 400 mbsf strongly influences pore-water DIC and magnesium concentration profiles. The linked succession of organic carbon mineralization and carbonate dissolution and precipitation patterns that we observe in the Bering Sea Slope sediment may be representative of passive continental margin settings in high-productivity areas of the world's ocean. ► Organic and inorganic carbon diagenesis during all burial stages in deep subseafloor. ► Characteristic succession of microbially mediated processes in subseafloor sediment. ► No diagenetic sig
ISSN:0009-2541
1872-6836
DOI:10.1016/j.chemgeo.2011.03.002