HR: 0800h
AN: U41A-0810    [Abstracts]
TI: Siberian lakes are growing in the north, shrinking in the south
AU: * Smith, L C
EM: lsmith@geog.ucla.edu
AF: UCLA, Department of Geography, 1255 Bunche Hall, Box 951524, Los Angeles, CA 90095-1524 United States
AU: Sheng, Y
EM: ysheng@esf.edu
AF: SUNY, College of Environmental Science and Forestry, Syracuse, NY 13210-2778 United States
AU: MacDonald, G M
EM: macdonal@geog.ucla.edu
AF: UCLA, Department of Geography, 1255 Bunche Hall, Box 951524, Los Angeles, CA 90095-1524 United States
AU: Hinzman, L D
EM: ffldh@uaf.edu
AF: Water and Environmental Research Center, University of Alaska, Fairbanks, AK 99775-5860 United States
AB: Archived Landsat MSS imagery from the early 1970's were compared with recent satellite data to inventory and track dynamic changes of ~10,000 large lakes (>40 ha) in West Siberia, following three decades of rising soil and air temperatures in the region. Between 1973 and 1997-98, the total number of lakes decreased from 10,882 to 9,712, a decline of 1,170 or ~11%. Most did not disappear altogether, but instead shrank to sizes below 40 ha. Total lake surface area decreased by 93,000 ha, a ~6% decline. One hundred and twenty-five lakes vanished completely, and are now re-vegetated as indicated by sharp increases in near-infrared reflectance. Subsequent monitoring of these former lakebeds using MODIS (1998-2004) confirms that none have refilled since 1997. The lakes are therefore considered to be permanently drained. The regional totals suggest an overall lake decline within this particular study area, but mask an interesting spatial pattern: In continuous permafrost, total lake area increased by 13,300 ha (+12%), and the number of lakes exceeding 40 ha in size rose from 1,148 in 1973 to 1,197 by 1997-98 (+4%). This trend of lake growth in continuous permafrost areas stands in sharp contrast with more southerly zones of discontinuous, sporadic and isolated permafrost, all of which experienced net declines in total lake number (-9%, -5%, and -6%, respectively) and area (-13%, -12%, -11%). These seemingly contradictory observations are unified if the process is understood as a continuum: Initial warming of continuous permafrost causes thermokarst and lake growth, followed by lake drainage as the permafrost degrades still further (enhancing lake infiltration and drainage to the subsurface). This mechanism is supported by the broad geographic pattern observed in Siberia (i.e. lake increases in continuous permafrost and losses where permafrost; and the fact that drained lakes are commonly found alongside undisturbed neighbors suggesting a spatially patchy process rather than regional water balance losses. Changes incurred by individual lakes must be interpreted with caution, as they are subject to complex, locally varying processes of thermal erosion, energy absorption and infilling and a single occurrence of lake change should not be used as proof of climatic change. Similarly, thermokarst lakes follow a well-known life cycle of formation, expansion and drainage quite independent of climate. For these reasons, it is important to examine broad-scale patterns in lake abundance, area, and drainage, as done here for western Siberia. Through study of thousands of lakes, net changes in their overall abundance and area may be identified and attributed to regional driving mechanisms such as climate and permafrost degradation.
UR: http://www.geog.ucla.edu
DE: 0702 Permafrost (0475)
DE: 0746 Lakes (9345)
DE: 1621 Cryospheric change (0776)
DE: 1823 Frozen ground
DE: 1855 Remote sensing (1640)
SC: Union [U]
MN: Fall Meeting 2005