HR: 1340h
AN: B53A-0918    [Abstracts]
TI:
AU: * Shakhova, N E
EM: nshakhov@iarc.uaf.edu
AF: International Arctic Research Center, University Alaska Fairbanks, Akasofu Building, Fairbanks, AK 99775, United States
AU: * Shakhova, N E
EM: nshakhov@iarc.uaf.edu
AF: VI Il'ichov Pacific Oceanological Institute, far Eastern Branch of russian Academy of Sciences, 43 Baltic Street, Vladivostok, 690041, Russian Federation
AU: Semiletov, I P
EM: igorsm@iarc.uaf.edu
AF: International Arctic Research Center, University Alaska Fairbanks, Akasofu Building, Fairbanks, AK 99775, United States
AU: Semiletov, I P
EM: igorsm@iarc.uaf.edu
AF: VI Il'ichov Pacific Oceanological Institute, far Eastern Branch of russian Academy of Sciences, 43 Baltic Street, Vladivostok, 690041, Russian Federation
AB: Importance of huge pool of old carbon stored within off-shore permafrost in Siberian region is determined by gradual mobilization of old carbon during permafrost degradation and its incorporation into modern carbon cycle in form of methane. Acceleration of this process due to both natural and anthropogenic disturbance of coastal environment may not only enhance a positive feedback to a global warming, but also can potentially cause rapid or even abrupt climate change on Earth. Theoretically, during times of marine transgression, the sub-sea permafrost could reduce in thickness and develops nearly isothermal conditions close to the melting point. This might occur early on after the marine transgression (high heat flow), or it might take up to several thousand years (low heat flow). Due to the time lag existing between the maximum heat flow and maximum permafrost transformation, the most drastic changes in thermal regime of permafrost might occur not at a warmest time, (for example, at Holocene optimum), but further. Moreover, the key changes in permafrost properties might not be reaching a phase transition stages, but more likely reaching permeability for gas on a larger scale. As sub-sea permafrost does not necessarily represent a rocklike ice-bonded layer, but is sometimes ice free under negative temperatures as its salinity increases, this allows permeability for upward migration of gases, stored within permafrost and/or beneath it. Our recent study in the East-Siberian Arctic shelf (2003-2006) detected CH4 super-saturation of surface water in some areas up to 10,000 % above background level, implying that strong air-to-sea fluxes must occur at times. It leads to significant increase in atmospheric concentrations of methane above the sea surface – up to 8 ppm (latitude specific monthly mean concentrations is 1.85 ppm). Our first wintertime data (April 2007) shows extremely high CH4 concentrations (up to 5.7 µmol l-1) in the surface water beneath the sea ice. Being commensurable with concentrations, measured during the wintertime in thermokarst lakes of Siberian Lowland, these values represent the highest CH4 concentrations, observed in the Arctic Ocean, and are comparable to those registered over decaying gas hydrate fields in the Sea of Okhotsk. The vertical distribution of dissolved CH4, as well as the size and number of CH4 bubbles, trapped within the sea ice, strongly indicate ebullition as a mechanism of CH4 transfer to the water surface. The areas, which should be considered as favorable for opening potentially perennial pathways for methane escape after over 6,000 year inundation, are following: large rivers taliks; a meandering river system (paleo- valleys), running across the shelf; so-called geological disjunctives (fault zones, tectonically and seismically active areas); sedimentary basins; completely submerged, or transformed into sea lagoons, thaw lake taliks.
DE: 0428 Carbon cycling (4806)
DE: 0490 Trace gases
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1621 Cryospheric change (0776)
DE: 4504 Air/sea interactions (0312, 3339)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting