Аннотация:Active layer develops in warm period of the year in cryolithozone
and occupies an intermediate position between the atmosphere and
permafrost. Active layer thickness (ALT) is sensitive to changes in
weather and climate. Although active layer formation mechanism and
natural factors affecting its spatial distribution are well studied in regional
scale, high local variability of ALT brings uncertainty to modelled results
and often forms multidirectional trends in interannual variations of ALT.
This study presents the results of long-term observations of the
active layer dynamics in various parts of Beringia palaeo-region. The data
are field measurements, conducted in framework of Circumpolar Active
Layer Monitoring (CALM) program and study materials of Dionisiya
field permafrost station (Anadyr area, Chukotka).
The sites, considered in this study, have mid- to long-term series of
observations (16 to 28 years) for active layer thickness and provided with
meteorological data. The key sites of the study are: 1) Kolyma lowland,
having 5 CALM sites, situated both in zonal (tundra and northern taiga)
and intrazonal (floodplain) landscapres; 2) Anadyr lowland (Dionisiya
field permafrost station) with 2 CALM sites, reflecting tundra foothills
and river lowland conditions; 3) Eastern Chukotka coastal plains (sedge
tundra); 4) NW Alaska, representing high-latitude polygonal tundra
(Barrow) and shrub tundra (Seward peninsula).
The analysis of interannual fluctuations of seasonal soil thawing
depth and summer (June-September) air temperatures revealed common
patterns and trends: the most of considered monitoring sites demonstrates
increasing of active layer thickness, which was observed in 1980-1990,
following increasing summer air temperature. This period was followed
by relative stabilization in 2000-2010 and continuation of active layer
thickening over the last several years. Several CALM sites in Kolyma
lowland and in Eastern Chukotka demonstrates continuous ALT
increasing during 2000-2010, even despite of summer temperatures
stabilization. Obtained data shows ambiguity of cryosphere response to
climate changes and requires necessity of further studies of interaction
between active layer and natural conditions.