Metabolic variability in seafloor brines revealed by carbon and sulphur dynamics

Brine fluids that upwell from deep, hot reservoirs below the sea bed supply the sea floor with energy-rich substrates and nutrients that are used by diverse microbial ecosystems. Contemporary hypersaline environments formed by brine seeps may provide insights into the metabolism and distribution of microorganisms on the early Earth or on extraterrestrial bodies. Here we use geochemical and genetic analyses to characterize microbial community composition and metabolism in two seafloor brines in the Gulf of Mexico: an active mud volcano and a quiescent brine pool. Both brine environments are anoxic and hypersaline. However, rates of sulphate reduction and acetate production are much higher in the brine pool, whereas the mud volcano supports much higher rates of methane production. We find no evidence of anaerobic oxidation of methane, despite high methane fluxes at both sites. We conclude that the contrasting microbial community compositions and metabolisms are linked to differences in dissolved-organic-matter input from the deep subsurface and different fluid advection rates between the two sites. DOI: 10.1038/NGEO47

An inverse model for reactive transport in biogeochemical systems : application to biologically-enhanced pore water transport (irrigation) in aquatic sediments

M.S.Herbert L. Windo

Metabolic variability in seafloor brines revealed by carbon and sulphur dynamics

Brine fluids that upwell from deep, hot reservoirs below the sea bed supply the sea floor with energy-rich substrates and nutrients that are used by diverse microbial ecosystems. Contemporary hypersaline environments formed by brine seeps may provide insights into the metabolism and distribution of microorganisms on the early Earth 1 or on extraterrestrial bodies 2 . Here we use geochemical and genetic analyses to characterize microbial community composition and metabolism in two seafloor brines in the Gulf of Mexico: an active mud volcano and a quiescent brine pool. Both brine environments are anoxic and hypersaline. However, rates of sulphate reduction and acetate production are much higher in the brine pool, whereas the mud volcano supports much higher rates of methane production. We find no evidence of anaerobic oxidation of methane, despite high methane fluxes at both sites. We conclude that the contrasting microbial community compositions and metabolisms are linked to differences in dissolved-organic-matter input from the deep subsurface and different fluid advection rates between the two sites. Seafloor mud volcanoes are high-flow environments characterized by vigorous discharge of fluidized mud and gas, and sometimes brine and oil, often at elevated temperature (∼50 • C; ref. 3). Over time, fluid flow rates decrease, transitioning some mud volcanoes into quiescent brine pools; brine pools can also form through lateral accumulation of brine into seafloor depressions. Seafloor brines exist in the Black, Red and Mediterranean seas 4-6 and the Gulf of Mexico Detailed insights into microbial activity in two brines from the northern Gulf of Mexico continental slope, a brine pool with a low fluid-flow rate (Brine Pool NR1; refs 3, Stratified profiles from the overlying sea water to ∼200 cm into the brine fluid were collected using a novel sampling device 8 . The chemical composition and salinity of the endmember brine fluids were similar 8 . The sharp salinity transition between hypersaline brine and sea water, and a higher suspended particle load underscored the rapid fluid-flow regime of the mud volcan

Comment on "A Persistent Oxygen Anomaly Reveals the Fate of Spilled Methane in the Deep Gulf of Mexico"

Kessler et al. (Reports, 21 January 2011, p. 312) reported that methane released from the 2010 Deepwater Horizon blowout, approximately 40% of the total hydrocarbon discharge, was consumed quantitatively by methanotrophic bacteria in Gulf of Mexico deep waters over a 4-month period. We find the evidence explicitly linking observed oxygen anomalies to methane consumption ambiguous and extension of these observations to hydrate-derived methane climate forcing premature