Methane concentrations in various marine environments

Abstract

Methane concentrations have been measured in the surface waters and at depth for several different marine environments. Measurements have also been made in rain water collected in Washington, D.C., over the Pacific Ocean, and in Hawaii. In tropical open ocean areas, surface water concentrations average 4.5 × 10−5 ml/l and decrease to values approaching 0.6 × 10−5 ml/l at a depth of 5000 meters. In natural anoxic conditions (i.e., Cariaco Trench, Black Sea, Lake Nitinat) concentrations can increase as much as four orders of magnitude. In the case of Lake Nitinat, 1.6 ml/l is found at a depth of 200 meters. Nearshore and bay concentrations can be 2–3 orders of magnitude higher than open ocean surface values. Open ocean surface waters are slightly supersaturated with methane, whereas estuary systems are highly supersaturated. Open ocean surface values remain fairly constant, whereas bay and river systems vary considerably, depending on the time of year, addition of pollutants, and tidal mixing. Rain water analyses yielded an average concentration of 5.0 × 10−5 ml/l for the Hawaiian and Pacific samples, and an average concentration of 8.8 × 10−5 ml/l was found for the Washington, D.C., area. Atmospheric methane concentrations over the open ocean remain fairly constant at 1.4 ppm. Atmospheric values in Washington, D.C., at NRL averaged 1.7 ppm.

Enhanced methane emissions from oil and gas exploration areas to the atmosphere – The central Bohai Sea

“…Due to natural physical and biological processes and anthropogenic activities, sea surface concentrations of dissolved CH 4 ([CH 4 ] for short) usually exceed atmospheric equilibrium (e.g., Lamontagne et al, 1973;Conrad and Seiler, 1988;Plass-Dülmer et al, 1993, 1995Reeburgh, 2007). In open oceans, CH 4 sources in shallow water depths are provided by microbial subsurface CH 4 generation taking place in zooplankton guts, the oxygen-deficient interior of particles, or under phosphate-limiting conditions (Karl et al, 2008;Damm et al, 2010).…”

Methane production induced by dimethylsulfide in surface water of an upwelling ecosystem

“…For instance, distinctive superficial peaks, some of which are located at the base of the photic layer, have frequently been described in marine environments (Lamontagne et al, 1973;Holmes et al, 2000), leading to the discussion on CH 4 sources in such layers. New insights reveal that CH 4 could be a by-product during the cycling of MPn or DMSP, but both mechanisms seem to be dependent on strong limitations or co-limitation of nutrients that trigger utilization of the compound (Karl et al, 2008;Damm et al, 2010).…”

“…Considerable focus is placed on excess quantities of biogenic CH 4 in surface oceans, apparently generated by a local methanogenesis in oxygenated surface waters (Karl et al, 2008;Rudd and Taylor, 1980). Given that CH 4 microbial production does not occur in oxic environments, this phenomenon is called the ''methane paradox'' (Wolfe, 1971;Lamontagne et al, 1973). A number of studies suggest that CH 4 excess in surface waters results from several in situ sources other than vertical advection of subsurface waters (Scranton and Brewer, 1977).…”

“…Earlier studies suggest that CH 4 production is carried out by microorganisms living within micro-environments which occur in dead cells, fecal pellets or large organisms (Scranton and Brewer, 1977). Other sites and mechanisms of CH 4 generation include zooplankton biomass (Traganza et al, 1979), the digestive tracts of fish (Lamontagne et al, 1973;Oremlad, 1979;Brooks et al, 1981) and the degradation of particulate organic matter (Karl and Tilbrook, 1994). Additional mechanisms for CH 4 formation in oxic environments are via methylphosphonate (MPn) cycling in subtropical gyres which are phosphate-stressed (Karl et al, 2008) and via DMSP in polar oligotrophic waters which are nitrate-stressed (Damm et al, 2010).…”

Ethylene and methane in the upper water column of the subtropical Atlantic

“…Advection of methane enriched coastal waters (Scranton & Farrington 1977;De Angelis & Lilley 1987;Cynar & Yayanos 1992) and riverine influence (Jones & Amador 1993) are also relevant processes. For the open ocean, biological in situ production is assumed to cause elevated methane concentrations in the upper water column < 500 m (Lamontagne et al 1973;Scranton & Brewer 1977;Traganza et al 1979;Burke et al 1983;Owens et al 1991). Compared to a global methane input to the atmosphere of about 540 Tg a −1 , methane release from the ocean is modest and suggested to be in the range of 3 to 18 Tg a −1 (Conrad & Seiler 1988;Khalil & Rasmussen 1983;Bange et al 1994).…”