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This paper addresses the latter issue, while the former remains under active debate. In real situations, DT is usually small and may have short- (e.g., seasonal) or long-term fluctuations that swamp the signal associated with climate warming trends. Dickens (2011) recently estimated 7x10 emissions are dominated by wetlands, ruminants, fossil fuel production, and rice cultivation (IPCC 2001), sources that fluctuate with season, human behavior, and other factors. 2004) to attribute ~3.75x10The geologic record is punctuated by warming events that may provide clues about future interactions between methane hydrates and climate change. Even over 10 yr, only gas hydrates close to the seafloor and initially within a few degrees of the thermodynamic stability boundary might experience dissociation in response to reasonable rates of warming. Changing climate: Geothermal evidence from permafrost in the Alaskan Arctic.
GHSZ sediments usually have low saturations of methane hydrate, except in permeable sand layers shown here with coarser-grained texture.
) might be liberated by widespread destabilization of climate-sensitive gas hydrate deposits trapped in marine and permafrost-associated sediments (Bohannon 2008, Krey et al. Even if only a fraction of the liberated CH Methane hydrate is an ice-like substance formed when CH4 and water combine at low temperature (up to ~25ºC) and moderate pressure (greater than 3-5 MPa, which corresponds to combined water and sediment depths of 300 to 500 m). (2009) question the role of gas hydrate dissociation in contributing to increased atmospheric CH The susceptibility of gas hydrates to warming climate depends on the duration of the warming event, their depth beneath the seafloor or tundra surface, and the amount of warming required to heat sediments to the point of dissociating gas hydrates.
Globally, an estimated 99% of gas hydrates occurs in the sediments of marine continental margins at saturations as high as 20% to 80% in some lithologies; the remaining 1% is mostly associated with sediments in and beneath areas of high-latitude, continuous permafrost (Mc Iver 1981, Collett et al. Nominally, methane hydrate concentrates CH by ~164 times on a volumetric basis compared to gas at standard pressure and temperature. Negative CIEs also undergird the clathrate gun hypothesis (CGH), which postulates that repeated warming of intermediate ocean waters during the Late Quaternary (since 400 ka) triggered periodic dissociation events (Kennett et al. Ice core data (Sowers 2006) and geologic studies (Maslin et al. A rudimentary estimate of the depth to which sediments are affected by an instantaneous, sustained temperature change DT in the overlying air or ocean waters can be made using the diffusive length scale 1 = √kt , which describes the depth (m) that 0.5 DT will propagate in elapsed time t (s). Changing concentration, lifetime and climate forcing of atmospheric methane.
Methane, not necessarily derived from gas hydrates, is emitted directly to the atmosphere at ebullition sites in shallow lakes within permafrost and probably in open water on shallow Arctic shelves. Geothermal conditions for gas hydrate stability in the Beaufort-Mackenzie area: The global change aspect.
Methane emitted at the seafloor at greater water depths is not likely to reach the atmosphere. Palaeogeography, Palaeoclimatology, Palaeoecology 98, 251-263 (1992).