METHANE AND HYDROGEN IN EAST PACIFIC RISE HYDROTHERMAL FLUIDS

Recently discovered hydrothermal vents at 21°N on the East Pacific Rise are discharging turbid waters at up to 400°C; mixtures of the plumes with ambient seawater contain significant amounts of dissolved H2 and CH4as well as He. The first grab samples of these waters were diluted 50‐100 foldbut they contained as much as 20 × 10−5 cc(STP) of H2 and 2 × 10−5 cc(STP) of CH4 per gram of water. H2/CH4 ratios in the vents increase with temperaturea result that is tentatively attributed to chemical equilibrium and/or the redox state of the individual waters. The phase diagram for the NaCl‐H2O surrogate‐seawater" system shows that liquid‐vapor separation may take place prior to dischargeand mixing of a vapor phase with entrained cooler sea‐water would profoundly alter original concentrations of volatiles as well as dissolved salts. H2 and CH4 ratios to basalt‐derived helium are respectively about 550 and 70 in these waters. The total fluxes from the world‐ocean ridge systemestimated from the He‐3 fluxare of the order of 1.3 × 109 m³/y for H2 and 1.6 × 108 m³/y for CH4. The CH4 flux so calculated is sufficient to replace the deep‐sea methane in ∼ 30 yearsimplying a very rapid bacterial consumption rate below the thermocline. Copyright 1979 by the American Geophysical Union."