Permafrost

Key words: Monitoring, permafrost, landscape, vegetation, climate.
134
The Influence of Freezeback Duration on Permafrost
Temperatures in Central Yakutia
Pavel Konstantinov, Masami Fukuda
(1.Melnikov Permafrost Institute SB RAS, Yakutsk, Russia
2.Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan)
Abstract: In the context of global climate change it is of practical importance to study changes
in the thermal state of upper permafrost. Upper permafrost temperatures are significantly
influenced by active-layer freezeback whose duration varies from year to year. The later is
complete freezing of the active layer, the shorter is the period of winter heat losses from the
ground and the higher is its mean annual temperature, and vice versa.
Investigations have been conducted since 1996 in the watershed between the Lena and
Kenkeme Rivers, 30 km north-west of Yakutsk. The study area is situated within the zone of
continuous permafrost with temperatures of –2.5 to –3.5°C.
In Central Yakutia, duration of active-layer freezing primarily depends on two
environmental factors: pre-winter soil moisture content and early-winter snow depth.
Winters with low pre-winter soil moisture contents and thin snow covers have higher
freezing rates and shorter duration of the freezeback period. In such winters during the
observation period, the rates of freezing and the lengths of the freezeback period were,
respectively, 1.0-3.8 cm/day and 60-110 days for the forest landscapes on sandy soils, 1.3-3.5
cm/day and 40-75 days for the forest landscapes on silty soils, and 0.8-3.7 cm/day and 70-110
days for the meadows on silty soils.
Winters with high pre-winter soil moisture contents and thick snow covers are
characterized by lower freezing rates and by longer duration of the freezeback period. During
the observation period, the rates of freezing and the lengths of the freezeback period in these
winters were, respectively, 0.4-2.5 cm/day and 83-145 days for the forest landscapes on sandy
soils, 0.5-2.1 cm/day and 80-130 days for the forest landscapes on silty soils, and 0.6-2.6
cm/day and 95-155 days for the meadows on silty soils.
Based on the results of investigations at the experimental sites, empirical relationships
between mean annual permafrost temperature and duration of active-layer freezing have been
obtained. Lengthening of the freezeback period by one month results in a warming of mean
annual permafrost temperatures by 0.8°C for sands and by 1°C for silty soils.
Key words: Permafrost, soil freezing, freezeback period, permafrost temperature