Pore-water sulfate concentration profiles of sediment cores from Krishna-Godavari and Goa basins, India

Abstract

Several cores from Krishna-Godavari (Western Bay of Bengal) and Goa (Eastern Arabian Sea) basins have been studied for pore water sulfate concentrations in order to understand and contrast the diagenetic processes. K-G sediments differ markedly from Goa sediments in pore water sulfate gradients and depth-integrated sulfate reduction rates. Significantly higher sulfate reduction rates in K-G sediments (3.6 to 15.8 nmol cm -2 day -1 ), compared to that in Goa sediments (0.011 to 0.94 nmol cm -2 day -1 ), can be attributed to higher sedimentation rates. Lower exposure time to oxygen for the organic matter in K-G sediments has preserved reactive organic compounds required for sulfate reducers and possibly methanogens. Authigenic carbonates with depleted carbon isotopic composition (δ 13 C = -48 to -50‰) at the base of the sulfate reduction zone in a core from K-G suggests anaerobic methane oxidation (AMO) process. The possibility, that the underlying methane gas hydrate zone is acting as a methane source for sulfate reduction can not be negated specially in light of the existing geophysical studies. Both methane and the fermentation products of organic matter degradation served as a substrate for sulfate reduction. However, a clear understanding of there relative importance needs further investigation.

An interdisciplinary investigation of a recent submarine mass transport deposit at the continental margin off Uruguay

“…Variability in sulfate reduction rates (SRR) and TOC concentrations play a role in shaping pore water profiles as well. As was shown by Mazumdar et al [2007], high SRs that lead to an enhanced preservation of TOC may fuel sulfate reduction and result in a steep SO 4 2− gradient compared to sites of low SRs and enhanced degradation of TOC by oxygen. However, variations in SRR and TOC with depth might explain concave profiles, but are not suitable to explain kink‐shaped profiles as observed at site GeoB 13804.…”

“…Given that the SO 4 2− gradient in a slide block differs from the gradient in the underlying sediment, the base of the MTD is usually characterized by an inflexion point in the SO 4 2− profile. Considerable variation in SO 4 2− gradients over small distances as well as SO 4 2− concentrations scattering around the concentration in bottom water over the whole lengths of m long gravity cores are known to occur in the study area (e.g., sites GeoB 2803‐3 and GeoB 2806‐5 [ Bleil et al , 1994]) and could reflect local differences in SRs, TOC concentrations, and SRR [ Mazumdar et al , 2007]. Thus, the prerequisites for the formation of kink‐shaped pore water profiles by mass wasting events at the continental slope off Uruguay are given.…”

Activity and community structures of sulfate-reducing microorganisms in polar, temperate and tropical marine sediments

“…Brief descriptions of the study sites are provided in Table 1. Samples were obtained from the upper 15 cm of sediment from each site, which corresponds to the depth range where bacterial sulfate reduction peaks (Abed et al, 2006;Mazumdar et al, 2007;Kristensen et al, 2008;Niemann et al, 2009;Robador et al, 2009;Sawicka et al, 2010;Holmkvist et al, 2014;Xu et al, 2014). After sampling, sediments were kept under anoxic conditions at in situ temperatures until further processing in the laboratory, which occurred within 1 week of sampling.…”

Seismic and heat flow constraints from the gas hydrate system in the Krishna–Godavari Basin, India

“…Seafloor temperatures (T Seaf ) were estimated using the linear regression from the in situ temperature measurements under NGHP Expedition-01 which is quite comparable with CTD measurements by Mazumdar et al (2007): T Seaf =13.09− 0.0062× z, where z is water depth in meters.. Temperature at the BSR depths (T BSR ) were estimated using the experimental thermobaric stability conditions for the methane-seawater system (Bouriak et al, 2000), which is based on pure methane and standard seawater (34 ppt).…”