Undiscovered Arctic gas hydrates: permafrost relationship and resource evaluation.
Abstract
Though ice-core studies show that multidecadal-scale methane variability is only weakly correlated with reconstructed temperature variations (Mitchell et al., 2010) methane emission to the atmosphere still consider as the most significant contributions to the global warming processes. Pockmarks, seeps, mud volcanoes and other features associated with methane fluxes from the seabed have been widely reported, particularly during the last three decades. On continental margins, seepage of hydrocarbon gases from shallow sedimentary layers is a common phenomenon, resulting either from in situ formation of gases (mainly methane) by bacterial decomposition of organic matter within rapidly accumulated upper sediments or from upward migration of gases formed at greater depths. Furthermore, processes associated with seabed fluid flow have been shown to affect benthic ecology and to supply methane to the hydrosphere and the atmosphere (Judd, 2003; Hovland and Judd, 2007). The most recent investigations testified that revaluation of the role of gas seeps and related gas hydrate formation processes in the Arctic environment is necessary for the understanding of global methane balance and global climate changes (Westbrook et al., 2009; Shahova and Semiletov, 2010). With respect to gas hydrate formation, due to the presence of relict permafrost the Arctic submarine environment holds a specific place that is distinct from the rest of the Ocean. Submarine gas hydrates in the Arctic may be confined to (1) relict permafrost occurrences on the shelf; (2) concentrated methane infiltration toward the seafloor (shallow-seated gas hydrates); (3) dissipated methane infiltration from great depths (deep-seated gas hydrates). Permafrost-related or cryogenic gas hydrates form due to exogenous cooling of sediment (intra- and sub-permafrost gas hydrates). It is also suggested that some parts of hydrates may be preserved owing to a self-preservation effect above the gas hydrate stability zone (GHSZ), which is shifted downwards due to permafrost degradation (Istomin et al., 2006; Dallimore and Collett, 1995). It is also believed that thermal conditions favourable to the formation of gas hydrates within permafrost have existed since the end of the Pliocene (about 1.88 Ma) (Collet and Dallimore, 2000). We estimate the total area of the distribution of GHSZ in the Arctic Ocean (including shelf areas, continental slope, and deep-sea troughs) to be as much as four million km2. Assuming the average gas amount per unit area in a separate gas hydrate accumulation to be 5x106 m3/km2 (Soloviev et al., 1999), it can be estimated that Arctic hydrates contain about 20 billion m3 of methane. The total area of GHSZ distribution within the Arctic seas off Russia is estimated to be about 1 million km2, with potential resources of gas in the hydrate state of about 2.36 billion m3. It should be noted, however, that field data are sparse and investigations are still producing surprising results, indicating that our understanding of gas hydrate formation and distribution within and out of sub-sea permafrost is incomplete. Estimates of the current and future release of methane from still undiscovered hydrates require particularly knowledge of the recent geological history of Polar Regions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGC52A..01C
- Keywords:
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- 0702 CRYOSPHERE / Permafrost;
- 1600 GLOBAL CHANGE;
- 3004 MARINE GEOLOGY AND GEOPHYSICS / Gas and hydrate systems