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Fig. 2: Methane flux to the atmosphere from the UKCS. Abstracts of oral presentations 63 Fig. 1: Average methane flux to the water column from dissolving pre-modern bubble seeps and diffusive flux from modern sediments. (N.B. exponential scale has been used.) Gas hydrate reservoir of carbon in the global system of subsurfacial carbon reservoirs B. M. Valyaev 1 1 Oil and Gas Research Institute, Moscow, Russia Gas hydrate (GH) reservoir of carbon takes a peculiar place in the global system of mobile subsurfacial reservoirs of carbone. This can be explaned not only by its huge volume – the recent estimations make up 5·10 17 g. Carbon reservoir in the atmosphere equels to the same volume. Hovewer, these reservoirs differ extremly both in the nature of oxidation – the reduction of carbon (the first contains mainly CH4, the second – CO2) and in its isotope (δ 13 C) composition (the methane carbone of gas hydrates (GHs) varies from 45 %0 up to - 70 %0, the carbone of the atmosphere carbone dioxide equels to – 8 %0).
64 Abstracts of oral presentations The gas hydrate reservoir of carbon is also characterised by some other features. It exist only in the glacial epochs. Warm epochs are not favorable both for the formation and conservation of gas hydrates. In the glacial epochs the zone of stability of gas hydrates (ZSGH) is widespread including the ocean floor. Hovewer, GHs turned up to be spread extremly enevenly. Large accumulations of GHs are discrete within the limits of ZSGH both in space and in the sediment section. The distribution of large GH accumulations is controlled by deep tectonic (geodynamic) factors and by the localized flows of deep hydrocarbon fluids (Dmitrievsky and Valyaev, 1998, 2001; and others). In many cases these localised flows appear to be through and are manifested on the sea bottom as hydrocarbon discharges (mud volcanoes, seepages, etc.). In these discharge sites subbottom GH fields are formed and specific microbial consortiums are developed as well. According to the data of deep water drilling within hydrocarbon discharges microbial consortiums are discovered in the sediment sections of ZSCH on different depths. High intensity of deep microbial life is discovered near the bottom of ZSGH – BSR – as well (Parkes et al, 2000; and others). Favourable conditions for the development of deep microbial life, caused by the energy of anaerobic oxidation of methane (hydrocarbon) are typical not only for ZSGH bottom. As it has turned out in the formation of GH accumulations on the different depths of the section of ZSGH pore sediments are filled with GHs only partially (up to 10-20 %, sometimes more). In that way in the medium of pore waters, saturated by the methane, the stability of GHs is not absolute, it is relative. Typically GH accumulations do not form the unique stratum – monolith, but they are spread in the form of numerous specific inclusions (different volumes) in the interval of sediment sections of ZSGH favourable for the formation of gas hudrates. Thus, the processes of the formation and the destruction of GH accumulations are accomponied by the development of different microbial consortiums. Gas hydrate accumulations and GH reservoirs on the whole are formed only owing to the utilization of the residial part of the ascending localized flows of hydrocarbon fluids. The methane excreted as a result of the destruction of GHs may migrate either up into the sea water or may be utilized by the microbial consortiums of the sediments. The important role of the GH reservoir of carbone in the stabilization of the conditions for the existance of microbial consortiums (deep life) in the marine sediments is evident. Gas hydrate reservoirs of carbon in the marine sediments should be considered as the most important reservoir of the carbon for the deep biosphere. Methane emission and associated biogeochemical consumption rates: How important are cold seep geostructures on a local and global scale F. Wenzhöfer 1 , J. Felden 1 , A. Lichtschlag 1 , D. deBeer 1 , T. Feseker 1,2 , J.P. Foucher 2 , G. Bohrmann 3 , F. Inagaki 4 , A. Boetius 1,5 1 Max Planck Institute for Marine Microbiology, Bremen, Germany 2 Centre Ifremer de Brest, Depart. Geosciences Marines, BP7, 29280 Plouzane, France 3 Research Center Ocean Margins, Bremen, Germany 4 JAMSTEC, Yokosuka, Japan 5 Jacobs University Bremen, Germany Cold seeps (e.g. mud volcanoes, pockmarks) are very interesting ecosystems, both from the biological and geological perspective. The rising fluid, mud and gas represent a window between the deep geosphere and the biosphere. Cold seeps can be an important natural source of the greenhouse gas methane to the hydrosphere and sometimes even the atmosphere. Recent investigations show that the number of active submarine cold seeps might be much higher than anticipated, and that gas emitted from deep-sea seeps might reach the upper mixed ocean. Unfortunately, global methane emission from active submarine seeps cannot be quantified because their number and gas emission rates are unknown. It is also unclear how efficiently methane-oxidizing microorganisms remove the methane. With regard to greenhouse gas effects, the study of cold seeps at continental margins is an important contribution to our understanding and quantification of the methane sources and sinks on earth. Concentrated around ocean margins, the focused emission of cold and often hydrocarbon-laden fluids from subsurface reservoirs into the oceanic hydrosphere is creating highly dynamic cold-seep ecosystems at the seafloor. These systems are shaped by a complex interplay of biological, geochemical, and geological processes. Associated with fluid outflow at seeps are chemosynthetic communities that utilize the chemical energy of reduced components such as H2S, CH4, and other hydrocarbons. The production of biomass by these communities can be several orders of magnitude greater than at non-seep sites on the nearby ocean floor. These chemosynthetic communities are nourished by the chemical energy – mostly methane - rising from subsurface sources and forming the basis of cold-seep ecosystems. In addition to these unique and highly specialized ecosystems, cold seeps are recognized by several morphological features, like pockmarks, hydrocarbon seeps on top of salt diapirs, asphalt volcanoes, brine pools, mud diapirs, and mud volcanoes. These geostructures are characterized by specific chemical environments, e.g. oxygen depletion within the first few millimeters of the
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9 th International Conference on Ga
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Program overview Monday September 1
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9 th International Conference on Ga
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Wednesday, Sept 17, 2008 09:00 - 09
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Thursday, Sept 18, 2008 09:00 - 09:
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