Cape Rogozhny
The grid “Cape Rogozhny”, 100x100 m, is located on Lower-Anadyr
(Nizhneanadyrskaya) Lowland at the northern coast of Onemen bay (6447 North
and 17658 East).
Relief of the area is hilly plain with altitudes 5 to 30 m above the water level in the
Bay. CALM grid is set at the flat hilltop slightly (at 0-3o) inclined southwestward
(Fig 1).
а) 08.09.1994
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б) 16.09.1995
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в) 11.09.1996
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Fig 1. Permafrost pattern and topography of the “Cape Rogozhny” grid in 1994-96.
The surface is represented by typical hummocky-moss tundra. Hummocks are
formed of cotton grass (Erioophorum vaginatum) dominating throughout the plain.
Hummock height is 15-20 cm. They cover 60 to 70% of the surface, the rest
occupied by inter-hummock depressions filled mostly by green and bog mosses
(Sphagnum sp.sp.) with admixture of lichens. Coverage of the dwarf shrubs within
the grid is 30-40 %; coverage of green moss is 20-30 % and of lichens – 5 to 10%.
Main producer of ground-level phytomass is cotton grass.
Soils of grid are peaty-gley with poorly developed (up to 10, rarely to 20 cm)
organic horizon underlain by peaty silt. Below fine-grained sands of LatePleistocene age up to 20 m thick are found, which in their turn are underlain by
glacial till of Middle-Pleistocene age.
The grid is located in the area of transition from moderately-continental to marine
climate subzone of the SubArctic climatic zone. Mean annual air temperature at
Anadyr weather station (30 km from the grid) is -7,7oС, mean annual precipitation
is 312 mm. Essential short-term ait-temperature oscillations are observed (file
TempAnadyr1951-01.xls).
The hydrochemical conditions of the grid in many respects are instituted by
closeness of marine coast. The type of atmospheric precipitation here is transitional
from maritime to continental. Rain and thawed snow water are of chloridehydrocarbon-sodium type with mineralization up to 45 mg/l. At inflow of thawed
and rain waters into the active layer, they get saturated by ions of calcium,
magnesium and hydrocarbonate, the mineralization rize up to 80-88 mg/l.
The grid is located in the continuous permafrost area. Taliks of hydrogenous type
are found only below the Onemen Bay and large lakes. Mean annual ground
temperature is about –5oC, the permafrost thickness is up to 150 m. Frost cracks
and ice-wedge, and spot-medallion formation are periglacial features developed
within the grid. At the adjacent area, the coastal processes are widespread: coastal
thermoerosion, thermocircues connected with massive ground ice occurrence.
Cryolithological structure of permafrost is variable. Immediately beneath the active
layer modern and Holocene ice wedges are lying, up to 2 m wide and up to 3 m
high. In fine-grained sands of Late-Pleistocene age syngenetic ice wedges are
tracked up to 2 m in width, with vertical expansion up to 20 m. Besides, the
syngenetic sandy and sandy-ice wedges are observed. In the lower stratigraphic
glacial complex massive ground ice is widely distributed.
Permanent 100x100 m grids have been established, with 10-m intervals between grid
nodes. Thaw depths were determined at each grid node (121) using a steel rod. The
measurements of the active-layer thickness were performed in inter-hummock
depressions according to the CALM procedure from 1994 to 2007 (Fig. 2). At the site a
surface quality of microhabitats such as tundra, vehicle tracks, frost boils etc. was
estimated. The site is supplied with a temperature data-loggers measuring air and soil
temperatures to the depth of 100 cm but measurements are irregular (see raw data in the
“temp_loggers” folder).
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Fig. 2. Dynamics of the end-of-season active layer thickness during the period of
monitoring.
As the experimental site is located within the limits of one landscape type - typical
moss-hummocky tundra, the spatial variation of active-layer depth is related to
higher thickness of organic layer (minimum thaw) and development of spotmedallions (maximal thaw). Low spatial variability of thaw depth is characteristic
for the grid. The average annual range of thaw depth variation is about 24 cm,
which constitutes 56% of the average thaw depth. Nevertheless interannual
variation of average thaw depth is rather high (INV = 23%). Disturbances of
vegetation and soil cover are mostly responsible for thaw depth spatial variability.
The natural ones are due to frost boils (3 of 121 grid nodes, avg. at 50 cm). Allterrain vehicles were another source of surface disturbance in the 80s (24 of 121
grid nodes, avg. at 45 cm). Despite a vegetative cover of the track fairly restored at
the beginning of 90s, the thaw depth remained some greater than in undisturbed
tundra habitats.
The matching of the data obtained for entire period of observations testifies to clear
dependence of active-layer depth on short-term fluctuations of mean annual air
temperature. The increase of mean air temperature in 1996 approximately by 3.5oC
has caused the increase of mean active-layer depth within the grid by more than on
6 cm. Nevertheless, such crucial fluctuations of the active-layer depth did not
result in any activation of periglacial processes within the grid. However, the
essential variations have taken place in activating coastal processes. It was in 1996
and 1997 that numerous thermocirques connected with massive ground ice, were
actively formed.
Case-study of vegetation-soil moisture-permafrost interaction was provided in
2001. Preliminary results are summarized in the “permveg.ppt” presentation.
Conclusions:
The end-of-season active layer thickness tends to increase during the period of
observations.
Temperature is the most important factor of interannual variability of active-layer
thickness. End-of-season thaw depth is strongly correlates with DDT0.5
Drain ways, surface disturbances and organic soil horizon depth are major controls of
spatial variations of end-of-season thaw depth
Influence of different factors on thawing process is seasonally specific.