HR: 08:30h
AN: C11A-03    [PDF]
TI: Effects of Freeze/Thaw Index, Air Temperature, and Snow Cover on Seasonal Freeze and Thaw Depths in Russia
AU: * Frauenfeld, O W
EM: oliverf@kryos.colorado.edu
AF: National Snow and Ice Data Center/CIRES, University of Colorado 449 UCB, Boulder, CO 80309-0449 United States
AU: Zhang, T
EM: tzhang@nsidc.org
AF: National Snow and Ice Data Center/CIRES, University of Colorado 449 UCB, Boulder, CO 80309-0449 United States
AU: Barry, R G
EM: rbarry@kryos.colorado.edu
AF: National Snow and Ice Data Center/CIRES, University of Colorado 449 UCB, Boulder, CO 80309-0449 United States
AU: Gilichinsky, D
EM: gilichin@issp.serpukhov.su
AF: Soil Cryology Laboratory, Institute of Physico-Chemical and Biological Problems in Soil Sciences, Russian Academy of Sciences, Pushchino, 142290 Russian Federation
AU: Etringer, A J
EM: etringer@nsidc.org
AF: National Snow and Ice Data Center/CIRES, University of Colorado 449 UCB, Boulder, CO 80309-0449 United States
AB: Seasonal freezing and thawing processes in cold regions play an exceedingly important role in ecosystem diversity, productivity, and the Arctic hydrological system in general. Long-term changes in seasonal freeze and thaw depths are also important indicators of climate change. Only sparse observational measurements of seasonal freeze and thaw depths are available in permafrost and seasonally frozen ground regions. However, soil temperature data are more readily and widely measured. Using mean monthly soil temperature data for 240 stations located throughout Russia for 1930\--1990, we have devised an interpolation method that determines the depth of the $0\deg$C isotherm based on soil temperature data measured at various depths between 0.2 m and 3.2 m. This methodology works remarkably well and we are subsequently able to work with a greatly improved sample size of stations. A comprehensive evaluation of these new data's long-term trends in Russia indicates that, in permafrost regions, active layer depths have been steadily increasing. In the period 1956\--1990 the active layer exhibited a statistically significant deepening by 11 cm. The changes in seasonally frozen ground are even greater: the depth of the freezing layer has exhibited a statistically significant decrease, resulting in 33 cm less frozen ground in 1990 than in 1956. Exploring potential causes for these changes\---freeze and thaw index, air temperature, and snow cover\---we are able to assess potential forcings of the observed changes. Multiple regression reveals that freezing index, the combined duration and magnitude of below\--freezing temperatures during the freezing season, has the greatest influence on the seasonal freeze depth. Similarly, mean annual air temperature is also significantly related to freeze depth, as is average snow depth. Analyses exploring causes for the observed changes in active layer depth show that measures of air temperature\---the thaw index and mean annual air temperature\---significantly influence the active layer, as does the previous winter's snow cover. In general these changes indicate that, as temperatures have been increasing globally in recent decades, permafrost is thawing to a greater depth during the warm season while less of the ground in non\--permafrost regions is freezing during the cold season. The changes in active layer depth and seasonal freezing depth seem to be related to changes in air temperature as well as snow cover. Potential direct consequences of these trends are increased river runoff and changes in discharge throughout the Russian Arctic drainage basin.
DE: 1600 GLOBAL CHANGE (New category)
DE: 1823 Frozen ground
DE: 1833 Hydroclimatology
DE: 1863 Snow and ice (1827)
DE: 3309 Climatology (1620)
SC: Cryosphere [C]
MN: 2003 Fall Meeting