HR: 0800h
AN: OS51B-0560    [Abstracts]
TI: Dissolved Methane Anomalies Over the East-Siberian Arctic Shelf: Signs of Gas Hydrate Decay?
AU: * Shakhova, N
EM: nshakhov@iarc.uaf.edu
AF: International Arctic Research center UAF, 930 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: * Shakhova, N
EM: nshakhov@iarc.uaf.edu
AF: Pacific Oceanological Institution FEBRAS, 43 baltic Street, Vladivostok, 690041 Russian Federation
AU: Semiletov, I
EM: igorsm@iarc.uaf.edu
AF: International Arctic Research center UAF, 930 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: Semiletov, I
EM: igorsm@iarc.uaf.edu
AF: Pacific Oceanological Institution FEBRAS, 43 baltic Street, Vladivostok, 690041 Russian Federation
AU: Romanovskii, N
EM:
AF: Moscow State University, Vorobievi Gori, Moscow, 119899 Russian Federation
AB: There is general agreement that global warming is due mainly to an increasing concentration of greenhouse gases, and positive feedback will release methane (CH4) from natural gas hydrates; these hydrates constitute the largest potential source of CH4 emission to the atmosphere. Over the Holocene (last 104 years) the largest temperature change occurred in the Arctic Siberian shelf seas; consequently, the Arctic region of shallow offshore permafrost may be critical to the problem of gas hydrate release; these hydrates constitute the largest potential source of CH4 emission to the atmosphere. Doubling of the atmospheric CH4 from present conditions requires release of less than 0.1% of the sub sea permafrost hydrate reservoir. The extensive Russian Arctic shelves play an especially important role because of their large area and usually shallow sea depth. We can suggest that the submarine permafrost under the tectonic fault might have decayed, in part or completely, allowing the release of CH4 from the gas hydrates. This instability stems from relatively large and frequent oscillations in temperature of waters on upper continental margins and glacial-eustatic sea regression, which has taken place on the shelf of the LS and ESS. For instance, the shallow bottom sediment (and underlying permafrost) in the study area has been warmed about 15°C after flooding before, prior to and during the Holocene optimum (about 6-8 kyr ago). The shoreline moved southward in the LS by 300- 400 km and in the ESS by 800-900 km. As a result, during the Holocene the Arctic shelf was covered by numerous thaw lakes, which later transformed into `thermokarst lagoons'. Submarine lake taliks, affected by processes of `bottom thermo-erosion' may be completely penetrated allowing methane release from disturbed gas hydrates. Acoustical data were collected using a `Furuno' (Japan) autonomous dual- frequency echo sounder system with frequencies of 50 kHz and 200 kHz and beam width 25 and 5 degrees respectively. According to these results we can expect disturbance or absence of sub-bottom permafrost within Dmitry Laptev Strait and north-western the Chaunskaya Bay,.where especially high values of dissolved CH4 were observed (up to 154 nM*). We associate formation of such warm local conditions not only with the impact of geothermal heat flow (­Y100mW/m) as was performed using a two dimensional finite-difference scheme (Tipenko et. al.,1999), but also with the energy input from the Lena River, which is one of the largest Arctic rivers. Thus we can suggest that the submarine permafrost under the fault zones might have decayed, in part or completely, allowing the release of CH4 from the gas hydrates. *The data were obtained in framework of the First and Second Russia-US cruises organized and supported by Headquarters of FEBRAS (`Environmental Changes in the East-Siberian region under climate effects and catastrophic processes'), IARC, Russian Foundation for Basic research and National Science Foundation.
DE: 0708 Thermokarst
DE: 0714 Clathrate
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL (0460)
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4806 Carbon cycling (0428)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005