HR: 14:55h
AN: C23B-06    [Abstracts]
TI: Permafrost Observatory near Gakona, Alaska. Local-Scale Features in Permafrost Distribution and Temperatures.
AU: * Romanovsky, V
EM: ffver@uaf.edu
AF: University of Alaska Fairbanks, 903 Koyukuk Drive P.O. Box 757320, Fairbanks, AK 99775 United States
AU: Yoshikawa, K
EM: ffky@uaf.edu
AF: University of Alaska Fairbanks, 903 Koyukuk Drive P.O. Box 757320, Fairbanks, AK 99775 United States
AU: Sergueev, D
EM: fndos@uaf.edu
AF: University of Alaska Fairbanks, 903 Koyukuk Drive P.O. Box 757320, Fairbanks, AK 99775 United States
AU: Shur, Y
EM: ffys@uaf.edu
AF: University of Alaska Fairbanks, 903 Koyukuk Drive P.O. Box 757320, Fairbanks, AK 99775 United States
AB: During the summer of 2004, the Geophysical Institute University of Alaska Fairbanks (GI UAF) established the Gakona Permafrost Observatory. This project is funded by the Office of Naval Research and the National Science Foundation. The Observatory is located in a large intermountain depression in the Copper River Basin. Permafrost in this area is widespread, in spite of its location near the southern boundary of the discontinuous permafrost zone. Together with the recently established Barrow Permafrost Observatory and with other GI UAF Permafrost Observatories, the Gakona Observatory will provide critically needed information on the permafrost response to recent and projected climate warming. The positioning of this observatory near the southern limits of permafrost distribution in Alaska makes this location very advantageous. With the growing possibility of near-future climate warming, permafrost integrity at this location will be affected first and will show significant changes in the very near future. In fact, at some locations within the area of observations permafrost already started to degrade and closed and, possibly, open taliks have been formed. Mean annual air temperature in this area was increasing from -3.5 C in the early 1950s to -1.6 C in the early 2000s. Several 10 m deep boreholes within the area with natural and disturbed surface conditions were equipped with thermistor strings and loggers to automatically monitor ground temperature dynamics with one-hour time resolution. Air temperature, snow depth, and soil liquid water content at four different depths together with 30 m deep temperature profile are also measured hourly at one location in the black spruce forest. The temperature data obtained in the first year of the project at this location show that permafrost temperature within the depth interval between 3 and 30 meters is practically constant at -0.6 C during the entire year. Obtained data also show that the partial thaw of permafrost from the top down is already underway and tightly relates to distinguish surface micro-topographical features. These features are elongated depressions (0.5 to 1.5 m deep and 10 to 100 m wide) with no trees and no moss on the ground surface. The depth to the permafrost table within these depressions are different at different locations and vary between 2 and 8 meters according to a survey by Duane Miller & Associates and to our temperature measurements in several boreholes. Repeated measurements of the permafrost table location within one of these depressions show increase in depth from approximately 3.5 m in 1989 to 5 m in 2004. As part of our initial survey, we applied geophysical methods (DC Resistivity and Ground Penetrating Radar) to investigate permafrost distribution in vertical and horizontal directions within the research area. Results obtained using DC Resistivity survey (Syscal Pro R1 switch 72 channel resistivity system) show that permafrost in the forest is stable and contain a limited amount of unfrozen water (resistivity is 600 ohm-m and higher, up to 1800 ohm-m). The lower boundary of permafrost locates at the depth of 50 to 60 meters. A talik (possibly open) was discovered under one of the mentioned above elongated depressions. The lateral extent of this talik is only 10 meters at the surface increasing with depth to several tens of meters.
DE: 0702 Permafrost (0475)
DE: 0708 Thermokarst
DE: 0768 Thermal regime
DE: 0925 Magnetic and electrical methods (5109)
SC: Cryosphere [C]
MN: Fall Meeting 2005