Stable isotope and geochemical record of convective hydrothermal circulation in the sedimentary sequence of Middle Valley, Juan de Fuca Ridge, Leg 139

Abstract

Carbon and oxygen isotope data of shallow carbonates at the active hydrothermal field are consistent with methane oxidation and, together with the presence of dolomite and Mg pre-water profiles, provide evidence for the advection of cold, oxidizing surface waters at shallow depths. From about five mbsf to the base of the cored section at Site 858 and throughout the hydrothermal reservoir at Site 857, the carbonate cement and nodules with δ13C values between -10‰ and -25‰ reflect sulfate reduction and/or thermal decomposition of organic matter. Delineates a system of large-scale convective hydrothermal circulation through the sedimentary sequence. In addition, smaller-scale fluid advection occurs in the shallowest part of the section. -from Authors