High concentrations of microbial methane and carbon dioxide are present in sediments cored during Leg 175 on the southwest African margin. Headspace carbon dioxide concentrations increase quickly below the seafloor. In contrast, headspace methane concentrations do not increase until after interstitial sulfate is depleted. Only a small fraction of the available carbon is microbially converted into interstitial gases. No geochemical evidence was found either for migration of hydrocarbon gases from deeper, thermally mature sediments or for formation of well-developed gas hydrate layers, even though seismic data suggest that both processes occur along this margin.
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Ms
175IR-121
Reproduced online:
31 August 2007