CONCLUSIONS

1. A unique, high-resolution data set consisting of pore-water concentration and isotopic data was gathered through the sulfate-reduction zone and within the uppermost methanogenic zone of Sites 994, 995, and 997 (ODP Leg 164).

2. Linear sulfate gradients are common within the sediments of the Carolina Rise and Blake Ridge, occurring at widely distributed ODP and piston-core sites.

3. Concave-up methane profiles, linear sulfate gradients, patterns of interstitial dissolved CO2 concentration, and extremely 13C-depleted 13CCO2 values consistently suggest that anaerobic methane oxidation is a significant sulfate-consuming process at all three ODP sites.

4. An inverse diagenetic model based on measured interstitial methane concentrations estimates that 35% of the total sulfate flux into the sediments at Site 995 is consumed by anaerobic methane oxidation.

5. Forty percent of the (nondiapir) sites sampled in the CR-BR area (by both piston coring and drilling operations) possess linear sulfate gradients larger than that seen at Site 995, implying that anaerobic methane oxidation may be responsible for even larger proportions of total sulfate depletion at these sites.

6. The wide occurrence of steep (linear) sulfate gradients over the Carolina Rise and Blake Ridge suggests that anaerobic methane oxidation is an important, additional process in consuming interstitial sulfate in these gas hydrate-associated sediments. Methane-rich sediments elsewhere, including those associated with gas hydrates, are expected to display similar chemistries.

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