Quantification of co-occurring reaction rates in deep subseafloor sediments
Document Type
Article
Date of Original Version
7-15-2008
Abstract
Net rates of biogeochemical reactions in subseafloor sediments can be quantified from concentration profiles of dissolved reactants or products and physical properties of the sediment. To study net rates of microbial activities in deep sediments, we developed a robust approach that is well suited to use over a broad range of sediment depths. Our approach is based on a finite-difference solution to a continuity equation that considers molecular diffusion, sediment burial, fluid advection, and reaction under the assumption of steady state. Numerical procedures are adopted to identify the maximum number of depth intervals with statistically different reaction rates. The approach explicitly considers downcore variation in physical properties and sample spacing. Uncertainties in the rate estimates are quantified using a Monte Carlo technique. We tested our approach using synthetic concentration profiles generated from analytical solutions to the continuity equation. We then applied the approach to concentration profiles of dissolved sulfate, sulfide, methane, and manganese in the 420-m thick sediment column of eastern equatorial Pacific Ocean Drilling Program Site 1226. Our results indicate that (i) sulfate reduction and iron reduction occur at most sediment depths, (ii) net methane production occurs in discrete depth intervals and (iii) manganese reduction occurs near the seafloor and deep in the sediments. These results provide quantitative evidence that multiple respiration pathways co-exist in the same depth intervals of these deep subseafloor sediments. © 2008 Elsevier Ltd. All rights reserved.
Publication Title, e.g., Journal
Geochimica et Cosmochimica Acta
Volume
72
Issue
14
Citation/Publisher Attribution
Wang, Guizhi, Arthur J. Spivack, Scott Rutherford, Uri Manor, and Steven D'Hondt. "Quantification of co-occurring reaction rates in deep subseafloor sediments." Geochimica et Cosmochimica Acta 72, 14 (2008). doi: 10.1016/j.gca.2008.04.024.