Methane plumes

Figure 4 shows results for the second methane plume detection with the physics-based signatures detection algorithm. Again, the clutter-matched filter fails to detect any methane at this level while the physics-based signatures algorithm detects a spatially compact, well-defined source. 

Methane August, 1980. The surface distribution of dissolved methane (nL/L, STP) in August 1980 is shown in Figure 3a. The highest surface concentrations were found near the entrance to Port Moller and near Unimak Pass (see Figure 1). At the entrance to Port Moller, concentrations of dissolved methane were greater than 2500 nL/L (about 35 times the equilibrium value) and decreased along the coast toward the northeast. The direction of the methane plume marks the mean drift of the coastal current. 

Dissolution of these metastable gas hydrates is a natural consequence of tectonic uplift of accretionary prisms at plate margins and is likely to be partly responsible for the extensive methane plumes above these sites (Herzig Hannington, 2000). The amount of methane that is slowly released from these hydrates can be enough to support a dependent biological community (Suess etal., 1999). 

Charlou, J.L., Donval, J.P., Fouquet, Y., Ondreas, H., Cochonat, P., Levache, D., Poirier, Y., Jean-Baptiste, R, Fourre, E., Chazallon, B., and Party, T.Z.L.S., 2004. Physical and chemical characterization of gas hydrates and associated methane plumes on the Congo-Angola Basin. Chemical Geology 205 405-425. 

Suess, E., Torres, M.E., Bohrmann, G, Collier, R.W., Greinert, J., Linke, L., Rehder, G, Trehu, A., Wallmann, K., Winckler, G, and Zuleger, E., 1999. Gas hydrate destabilization enhanced dewatering, benthic material turnover and large methane plumes at the Cascadia convergent margin Earth and Planetary Science Letters, 170 1-15. 

Example 3.4 A turbulent fire plume is experimentally found to bum with 10 times the required stoichiometric air up to the tip of the flame. It is also measured that 20 % of the chemical energy is radiated to the surroundings from the flame. The fuel is methane, which is supplied at 25 °C and burns in air which is also at 25 °C. Calculate the average temperature of the gases leaving the flame tip. Assume constant and equal specific heats and steady state. 

Ishibashi 1., Wakita H., Okamura K., NakayamaE., Feely R. A., Lebon G. T., Baker E. T., and Marumo K. (1997) Hydrothermal methane and manganese variation in the plume over the superfast-spreading southern East Pacific Rise. Geochim. Cosmochim. Acta 61, 485-500. 

Grossman E. L., Cifuentes L. A., and Cozzarelli I. M. (2002) Anaerobic methane oxidation in a landfill-leachate plume. Envirofi. Sci. Technol. 36, 2436—2442. 

Overall, this refined use of hydrogen concentrations supported the results of the bioassays and the complex system of redox zones inferred from the distribution of dissolved redox-sensitive species. The Grindsted Landfill (DK) plume is host to all of the proposed redox reactions, but also to secondary oxidation-reduction reactions involving ammonium, methane, manganese oxides, ferrous iron, and sulfides. 

Neptune s large satellite Triton, which has a very thin nitrogen atmosphere with clouds, plumes, and haze, an extremely cold surface with nitrogen, methane, carbon monoxide, and carbon dioxide ices which interact with the atmosphere, and a fairly high mean density, make it seem more like Pluto than the other satellites of Neptune and those of Saturn and Uranus. Not enough is known about Pluto to explore these similarities this probably awaits future missions to Pluto, especially the New Horizons mission that NASA hopes to launch in 2006. 

Pauli, C.K., Spiess, F.N., Ussier, W. and Borowski, W.A., 1995. Methane-rich plumes on the Carolina continental rise association with gas hydrates. Geology, 23 89-92. 

Within this setting, in shallow coastal water conditions, consortia of bacteria set up microbial mat columns to exploit the supply of sulphate and nitrate from water. In the muds below the mats, methanogens were active, and above them methane-oxidizing bacteria. The waters were enriched chemically by contributions from hydro-thermal water plumes, either from the laterally equivalent beginnings of Reliance Fm volcanism elsewhere in the basin, or from more distant oceanic sources. Photosynthetic green sulphur bacteria may have oxidized H2S to S°, whereas sulphate and sulphur reducers operated in the reverse direction. 

As noted earlier, the highest surface concentrations of methane were near Port Moller, where the concentration exceeded 1500 nL/L in July 1976. Measurements were not obtained near the mouth of the estuary in September 1975, so comparable values were not available, but the coastal plume appears weaker than that seen in July 1976 (compare Figures 7a and 8a). Over the remainder of the embayment, concentrations were generally less than 100 nL/L, except as previously noted in the coastal zone. 

Maximum concentrations of methane were again observed in the near-bottom waters of St. George Basin, however, the relatively large amounts observed in 1980-1981 were significantly lower in July 1976 (Figure 8b). The near bottom plume was more pronounced in October 1975, but maximum concentrations of 600 nL/L were below the concentrations seen in 1980-1981. Processes Controlling the Distribution of Methane... 

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