We report dissolved sulfide sulfur concentrations and the sulfur isotopic composition of dissolved sulfate and sulfide in pore waters from sediments collected during Ocean Drilling Program Leg 204. Porewater sulfate is depleted rapidly as the depth to the sulfate/methane interface (SMI) occurs between 4.5 and 11 meters below seafloor at flank and basin locations. Dissolved sulfide concentration reaches values as high as 11.3 mM in Hole 1251E. Otherwise, peak sulfide concentrations lie between 3.2 and 6.1 mM and occur immediately above the SMI. The sulfur isotopic composition of interstitial sulfate generally becomes enriched in 34S with increasing sediment depth. Peak d34S-SO4 values occur just above the SMI and reach up to 53.1 per mil Vienna Canyon Diablo Troilite (VCDT) in Hole 1247B. d34S-Sigma HS values generally parallel the trend of d34S-SO4 values but are more depleted in 34S relative to sulfate, with values from -12.7 per mil to 19.3 per mil VCDT. Curvilinear sulfate profiles and carbon isotopic composition of total dissolved carbon dioxide at flank and basin sites strongly suggest that sulfate depletion is controlled by oxidation of sedimentary organic matter, despite the presence of methane gas hydrates in underlying sediments. Preliminary data from sulfur species are consistent with this interpretation for Leg 204 sediments at sites not located on or near the crest of Hydrate Ridge.

Sediment depth is given in mbsf. For carbon isotopic composition of dissolved carbon dioxide (d13C-CO2) see Torres and Rugh (2006) dataset: doi:10.1594/PANGAEA.774441. Sulphate concentrations and alkalinity are given in Tréhu et al. (2006, doi:10.2973/odp.proc.sr.204.101.2006)

Supplement to: Borowski, Walter S (2006): Data report: Dissolved sulfide concentration and sulfur isotopic composition of sulfide and sulfate in pore waters, ODP Leg 204, Hydrate Ridge and vicinity, Cascadia Margin, offshore Oregon. In: Tréhu, AM; Bohrmann, G; Torres, ME; Colwell, FS (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 204, 1-13