environment sustainability warming and per… · m.v. lomonosov moscow state university, leninskie...
TRANSCRIPT
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RUSSIAN GEOGRAPHICAL SOCIETY
FACULTY OF GEOGRAPHY, M.V. LOMONOSOV MOSCOW STATE UNIVERSITY
INSTITUTE OF GEOGRAPHY, RUSSIAN ACADEMY OF SCIENCES
No. 01 [02]
2009
GEOGRAPHY ENVIRONMENT SUSTAINABILITY
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Vyacheslav N. Konishchev M.V. Lomonosov Moscow State University, Leninskie gory, 119991, Moscow, Russia E-mail: [email protected]
CLIMATE WARMING AND PERMAFROST
ABSTRACT
The purpose of the paper is to discuss re-sponses of the cryolithozone to two different scale warming events: (1) climate warming of recent decades at the end of the 20 t h and the beginning of the 21 s t century, and (2) climate warming in the interval between the cryochron in the late Pleistocene through the Holocene. Changes in several permafrost parameters that occur with climate warm-ing were influenced by the entire complex of landscape characteristics and landscape components that also change under climate warming. This phenomenon may explain why in certain landscapes during climate warming aggradational changes, such as a decrease or stabilization of permafrost temperatures, decrease in the thickness of the seasonal freezing/thawing layer, and increase in the ice content of the upper permafrost layers, are present along with degradation processes (e. g., permafrost temperature increase, increase in the area of taliks, etc.)
KEYWORDS: climatic and non-climatic factor of heat exchange, lateral and frontal permafrost degradation, protective layer, ice complex.
PROBLEM STATEMENT From very early phases of its development, permafrost science has focused on the cryolithozone (permafrost) response to climate change. This problem became especially important in the early 1960s, when the issue of global warming emerged.
To date, dozens of papers and monographs and many international and Russian conferences specifically targeted changes in the cryolithozone resulting from global climate change. For more than 15 years, countries with permafrost or even short-term seasonal episodes of freezing of soils and the upper layers of the lithosphere within their territory have been engaged in several international programs, e. g., Circumpolar Active Layer Monitoring (CALM) and the Thermal Status of Permafrost (TSP).
The collective research effort has established that climate is not the only factor that influences the important characteristics of permafrost, namely, the average annual temperature of frozen soils at the depth of zero annual amplitude (tav), thickness of the seasonal thawing layer (STL), and other parameters. The impact of air temperatures, snow cover, different types of vegetation, soils, lithology, and water content on these permafrost parameters, other properties of frozen soils, and cryogenic processes (thermokarst, thermal contraction cracking, etc.) have been quantitatively evaluated. Geographic patterns of changes in the frozen soil layers as a factor of landscape and geological properties have been relatively well studied. Several models that attempt to forecast changes in the cryolithozone within different time frames during the 21 century have been developed.
Current assessments of the cryolithozone response to the contemporaneous and
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projected changes in climate do not
sufficiently account for heat exchange
between permanently frozen soils (PFS)
and the external environment. All external
factors, including climatic, do not impact PFS
directly as in the case on a glacial surface, but
act through a system of different layers, such
as snow, vegetation, top soil, active soil layer,
i. е., through landscape and its components.
Some authors differentiate factors of heat
exchange between PFS and the atmosphere
into temperature and non-temperature or
climatic and non-climatic.
Surface conditions and the intensity of
their influence change with annual seasons.
Directional climate change parameters
(specifically, an increase in the average annual
summer or winter air temperatures) influence
other components of the environment
affecting the heat exchange between
PFS and the atmosphere. Therefore, PFS
characteristics react to the entire complex of
parameters that are changing in response to
changes in the landscape climate.
An array of positive and negative feedbacks
appears as a result. In certain conditions,
these multidirectional feedbacks manifest
themselves in a varying intensity of the PFS
reaction to changes in air temperatures and
in a different character of the responses.
Numerous mechanisms that determine
these relationships are poorly understood at
the present time. For example, the influence
of snow cover on permafrost temperatures
is relatively well studied, but the influence
of the snow cover structure, its density,
porosity, and thermal-physical characteristics
that undergo winter changes and ultimately
influence the PFS thermal properties are
completely lacking in understanding.
Changes in surface conditions that
accompany warming or cooling may strongly
transform the direction of the freeze and
thaw process and the growth or degradation
of permafrost. In some landscapes, these
changes will act in the same direction as
the direction of climate trend enhancing its
influence, while in other conditions changes
will act in opposing directions resulting in a
weakening of the influence of climate trend
[Koreisha, Vtyurin, Vtyurina, 1997].
Background data on this important theoretical
conclusion have been obtained as early as in
1930th. A detailed analysis of spatial changes
in discontinuous cryolithozone in the basin
of the Selemdja river (Russian Far East)
established that "enhancement of permafrost
along with its degradation within the same
limited in size piece of land" [Kudryavtsev,
1939; Shvetsov, 1959] may be occurring
depending on geological, geomorphological,
hydrogeological, hydrological, and
geobotanical environment.
It may be assumed that spatial patterns
are analogous to temporal patterns of the
cryolithozone formation.
Despite the long established by permafrost
science fact that complex and ambiguous
dependencies between climatic and
permafrost characteristics exist, modern
literature still has elements of a simplified
approach to the analysis of the relationships
between thermal and other characteristics
of PFS, e. g., temperature and climatic
parameters.
Most of forecast models that describe
relationships between climate and permafrost
are mono-factorial and they only account for
direct links of the cryolithozone to isolated
environmental parameters, in particular, to
air temperature; some models, in addition,
include precipitation and thickness of the
snow cover at best.
The IPCC report [2008] contains examples of
such simplified approach to the assessment
of changes in the cryolithozone due to
global warming of the recent decades.
The purpose of the paper presented
herein is to demonstrate, using specific
examples from different regions of the
cryolithozone, ambiguous responses of
permafrost properties to two different-scale
climate warming events, i. е., warming of
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recent decades and warming of the late
Pleistocene - Holocene.
CHANGES IN CRYOGENIC CONDITIONS
IN ISLAND AND MASSIVE-ISLAND
PERMAFROST ZONES
In the southern belt of the cryolothozone
in northern Europe, West Siberia, Canada,
and Alaska, permafrost may be found in
isolated or relatively extended areas of peat
hummocks and raised peat mounds that are
referred to as "palsas" in literature.
Recently, in such areas of different
countries (USA, Canada, Sweden, Finland,
and Mongolia), detailed studies on palsa
dynamics were conducted.
In 1933, a special field expedition was
organized by the Commission of the Academy
of Sciences of the USSR to identify the southern
permafrost border near the city of Mezen,
Kanin coastline of Mezen Bay. This expedition
obtained fundamental results on the dynamics
of frozen peat mounds [Datsky, 1937]
In this area, permafrost is represented by
1 -2 m high peat mounds 15 x 20 m in area.
Authors explain negative temperatures in
the peat mounds by the winter wind snow
removal off the tops of the hummocks. Some
hummocks are in a stationary state, but most
of the hummocks are degrading, i. е., they are
decreasing in size as a result of permafrost
thawing both on the slopes adjacent to
waterlogged lowlands and from the bottom.
However, the upper permafrost boundary
within this hummocky area, i. е., the thickness
of the STL, is relatively consistent (about
0,5 m) and exists at a permanently stable
state till the moment of almost complete
permafrost thawing and hummocks
degradation and collapse.
Therefore, hydrological properties, i. е., the
inundation level of wetlands that surround
the hummocks, not the temperatures,
may be the main factors that influence the
collapse of the hummocks.
The authors of this fundamental research have
still regarded the 1916-1930 climatic change
with temperatures 10 С higher than in 1883-
1915, to be the main factor of permafrost
degradation. In this work, for the first time a
connection between climate warming and the
degradation of permafrost in peat hummocks
has been established. Also, the research
has demonstrated that human impact (a
disturbance of hummocks surface, destruction
of vegetation, livestock grazing) may enhance
degradation processes in most cases.
Numerous research efforts that use modern
methods (time sequence aerial photography
comparison, geophysics, stationary
observations) to study peat areas and frost
mounds within the spread of island and
massive-island permafrost near its southern
boundary have been undertaken in different
areas of Finland, Sweden, Norway, Alaska,
and Canada. These studies have confirmed,
in general, the results of the field expedition
to Mezen region, and allowed to better
understand the climate change dynamics of
this type of permafrost. In all these regions,
a decrease in the area of frozen peatlands
represents a prevailing tendency that
reflects permafrost degradation. However,
the degradation of frozen peatlands occurs
in a lateral direction, i. е., from the sides,
and the speed of thermokarst development
depends upon the level of inundation of
surrounding wetlands. On average, the speed
of the degradation during the last 50 years
was 1% of the total area considered. Within
relatively well drained wetland sites, heaving
and growth of new peatlands and mounds
is occurring. Sometimes the degradation
of permafrost on one side is accompanied
by freezing, heaving, and the increase in
the size of the peat mass on the other side
[Kershow, 2003] Positive temperature change
trends do not practically influence the depth
of seasonal thawing within degrading or
growing peatlands. Some authors state that
the scale of permafrost degradation within
peatland areas does not at all depend on
changes in average annual temperatures,
but is influenced by local factors [Beilman,
Robinson, 2003].
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Furthermore, certain observations prove that
permafrost dynamics within peat areas is not
defined by climate trend, but is determined
by a combination of specific summer and
winter weather patterns, which promote
permafrost preservation and the formation
of new frozen soils. The southern belt of the
cryolithozone of Timan-Pechora region during
the last 60 years [Osadchyi, Osadchaya, 2008]
may represent one of the examples. Another
example is the modern conditions of the
Lapland region in Finland, where the increase
in wind activity accompanied by the removal
of snow from the mounds 90 cm and higher
therefore promoting the formation of frozen
islands has led to the formation of new palsas
[Ronkvo, Seppala, 2003].
REACTION OF PERMAFROST TO MODERN
CLIMATE CHANGE IN OTHER REGIONS
Scientific data summarized by the IPCC
[2008] report an increase in permafrost
temperatures at the depth of zero annual
amplitude (tav) during recent decades in
different regions of the cryolithozone of
Alaska, northern Canada, northern European
part of Russia, northern Scandinavia, Tibetan
Plateau, Mongolia, and Tien Shan. The
increase in annual air temperatures along
with changes in the snow cover have been
suggested as the main factors of such
permafrost response.
These data describe permafrost developed
on mineral soils and characterize frozen
soils within autonomous landscapes; these
data differ from the results presented in the
previous section that pertain to frozen peat
areas.
In cases when temperature observations
in boreholes encompass a more complete
spectrum of landscape conditions of a site,
it appears that PFS respond to changes in
air temperatures (to warming) with varying
intensity and in a different pattern.
Earlier, we have demonstrated that positive
responses, i. е., positive feedbacks, to climate
warming, are present in autonomous or close
to autonomous, environments. However,
monitoring of permafrost temperatures in
Central Yakutia [Skryabin,Skachkov,Varlamov,
1999] indicated negative feedbacks in
subaqueous or superaqueous subordinate
environments, such as floodplains, low
terraces, shallow valleys, and inter-hummock
depressions [Konishchev, 2003].
Recently (the last 10 to 20 years), in the area
of Chulman basin (Aldan shield), geothermal
data showed a temperature increase tav of
0,1-0,3°C at the depth of 40 m in 23% of
the watershed boreholes. In most boreholes
located in intact natural conditions, a quasi-
stationary thermal regime is preserved at
the depths of 20-50 m, which does not
respond to the increase in average annual
temperatures during the last 20 years.
In some cases, in river floodplains and valleys
within sites with a pit-and-mound relief,
temperature decreased by 0,1 °C temperature
decrease (tav) to the depths of 20-40 m
[Zheleznyak, Zavadsky, Mitin, 2006] These
data undoubtedly confirm an existence
of an inter-landscape differentiation of tav
feedbacks to climate change.
Subordinate (subaqueous) landscapes may
have different feedbacks to climate warming
because, unlike autonomous landscapes,they
may develop protective responses including
an increase in the topsoil water content,
more intensive growth of hygrophilous
plants (moss), accrual of organic material in
the topsoil accumulative horizon, etc.
The extent of this phenomenon in relation
to different temperature and cryolithological
regions of the cryolithozone is hard to
evaluate at the present time due to a limited
volume of actual research data. In any case,
in the zone of discontinuous permafrost
(on mineral substrates), the landscape
differentiation in permafrost response
to climate warming and especially of its
southern part should be very specific.
In discontinuous permafrost area, a
temperature increase and melting of PFS
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from the surface to the depth of several
meters, results in the development of
the residual thaw layer. This process was
detected by thermometric observations
in frozen mineral soils in the Urengoi gas
condensate field (West Siberia) [Vasiliev,
Drozdov, Moskalenko, 2008]. Unlike island
and massive-island permafrost where
frozen peat hummocks are degrading in
a lateral direction, in the northern part of
discontinuous cryolithozone, mineral layers
are degrading in a frontal direction, i. е., from
the top to the bottom.
Indicators of the cryolithozone feedbacks
to the modern climatic changes based on
monitoring include variations in the depth
of the seasonal freezing-thawing and the
temperatures of frozen soils at the depth
of zero annual amplitude (tav) (as a rule, 10
to 15 m). It is important to identify spatial-
temporal relationships between these
parameters.
Long-term stationary observations (over
30 ears in duration) in the northern part of
Western Siberia have showed that the depth
of the STL has a relatively weak response
to climate warming compared to annual
average temperatures of frozen soils (tav). The
temperature response of frozen soils within
some landscapes may be more pronounced
than a trend in air temperatures, which may
be influenced by an increase in multi-annual
snow deposits [Pavlov, Moskalenko, 2001].
Even more radical conclusion has been
reached in research activities conducted in
the northern part of West Siberia [Vasiliev,
Drozdov, Moskalenko, 2008]: a response of
dominant permafrost landscapes (peatlands
and wetlands) to climate warming may
be proceeding in two opposite directions,
i. e. maximal increase in seasonal thawing
accompanied by a minimal change in tav or
maximal increase in tav at a minimal change
in the STL thickness.
to 2007) the top soil and permafrost
temperatures at the depth of 0,7 m at the
site near Cape Franklin in Alaska increased
notably by 1,774°C and 2,34°C, respectively
following 1,334°C increase in air temperatures.
At the same time, the depth of the STL (with
an average thickness of 0,577 m) decreased
by 0,036 m. One of the main reasons for this
"discrepancy" is a growth of vegetation at the
medallion spots, or so called "greening effect
of the Arctic" [Daanen, Romanovsky, Walker,
and LaDouceur, 2008], which substantially
decreases absorbed solar radiation thus
decreasing the thawing index.
These examples indicate that the analysis
of the contemporary dynamics of the
cryolithozone under climate change
(warming) and forecast scenarios for
changes in the cryolithozone should
account for an entire array of properties of
a landscape and its isolated components
that change in response to the climate
change. The effects that counteract
manifestations of a leading process deserve
special attention. In different regions of
the cryolithozone, these relationships
differ and are very poorly understood;
their analysis should be based on regional
characteristics of the system "climate-
landscape-cryolithozone".
DYNAMICS OF PERMAFROST AT THE
END OF LATE PLEISTOCENE THROUGH
HOLOCENE
In northern Eurasia, a major scale degradation
of the late Pleistocene cryolithozone began
at the end of the late Pleistocene and the
Holocene interval. During the last 10 to
12 thousand years, the cryolithozne area has
shrunk by more than a factor of two. On the
Russian Plain and in West Siberia, the southern
boundary of the cryolithozone moved from
48° northern latitudes to its contemporary
boundary, i. е., several hundreds kilometers
to the north [Velichko, 2002].
Spotted (medallion) tundra permafrost has
a very specific response to the modern
warming. During the last 30 years (1977
Not least radical changes took place within
the modern area of the cryolithozone, the
most impressive of which is the evolution
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Figure 1. Outcroppings of the ice complex
(low course of the Yana river, left bank, photographed by the author, 1967)
of the ice complex, i. е., ice-rich frozen soils
several dozens meters in thickness (Figure 1).
The ice complex sediments have most
widely spread in the late cryochron (15 to
18 thousand years ago), when sea regression
exposed the enormous areas of the Arctic
Ocean shelf zone, including the Laptev and
other seas. In these exposed areas and within
the territory of East Siberia, the accumulation
of the ice complex sediments took place. The
distribution of the ice complex sediments is
presented in Figure 2; the sediments of
the shelf zone areas have been destroyed
during the Holocene sea transgression and
are not shown on the map.The ice complex
sediments were forming under very severe
climatic conditions of the late cryochron;
in the northern part of Yakutia, average
temperatures of frozen soils (tav) were -25 ~ -28°C, reaching, in some areas, -30°C.
In Central Yakutia, the ice complex sediments
were forming at temperatures below
-10°C; with even lower air temperatures
[Konishchev, 1997]. At the present time,
the annual temperatures of permafrost in
these regions are -12 ~ -14°C and -3 ~ -5°С,
respectively.
A sharp increase in permafrost temperatures
was not the single consequence of the
cardinal climate change at the end of the late
Pleistocene cryochron - Holocene transition.
One of the main processes of the relief-
forming ice complex sediment evolution
during the last 12 to 13 thousand years
was their thermokarst erosion differentiation
and a formation of numerous thermokarst-
erosion depressions.
Currently, in the North and Central Yakutian
lowlands, the ice complex remnants (i. е.,
ostanetsy or yedomas) and alas basins several
dozens of kilometers in size represent the
dominant relief forms along with river valleys.
Published data contain various assessments
of areas of the ice complex remnants in North
and Central Yakutian lowlands,and alas basins
(thermokarst erosion). In the coastal lowlands
of Yakutia, thermokarst-erosion basins cover
approximately 60-70 % of the total lowland
area; in Central Yakutia, alase basins cover
10-20 % of the total region area [Bosikov,
1978]. Thermokarst-erosion basins in Yana-
Omoloi watershed area occupy 35-40 to
60-70 % of the lowland area [Gordeev, 1971].
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Figure 2. Spatial distribution of ice complex deposits in Russia.
Compiled by the author and N.A. Koroleva based on [15, 28, 31 ]
In Yana-lndigirka lowland, thermokarst-lake surfaces are spread over 65-75 % of the area, whereas, remnants of the ice complex occupy only 25 % [Lomachenkov, 1965]. In the Kolyma lowland, remnants of the ice complex are found on approximately 4 1 % of the total lowland area. Alases in Central Yakutia (theTungulu terrace and its juncture with the Abalakh terrace) cover from 15-20% to 30-50 % of the ice complex area [Ivanov, 1981;Torgovkin, 1988].
Despite an approximate nature of these
assessments, their comparison allows one to
conclude that surfaces composed of the ice
complex in the lowlands of Northern Yakutia
are notably more affected by thermokart
processes than within the territory of the
Central Yakutia lowland.
Paleogeographic data on the Holocene history together with direct observations indicate that alas depressions are practically not developing at the present time in
Central Yakutia with the exception of alases that formed as a result of anthropogenic impact [Katasonov, 1979]. Alases actively grew due to the thermal abrasion in the past, specifically during a period of inundation of alas depressions in the late 1930s.
At the present time, an expansion of alas
basins is detected within the territory of
Yana-lndigirka lowland [Tolstov, 1966].
The main cause for the formation and development of alases in Northern Yakutia and further to the south of this area within the Central Yakutian lowland was not the warming or some other temperature factors alone, but the inundation of the territory expressed by the formation of lakes. If in the northern part, this factor was acting constantly from the very end of the late Pleistocene through the entire Holocene, the aridization period in Central Yakutia started in the first half of the Holocene and is continuing through the present time [Katasonov, 1979].
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The accumulation of the ice complex
sediments has reached its completion at the
end of the late cryochron; from that time on,
apical surfaces of ostantsy (or yedomas) have
not been subject to denudation, including
thermokarst and erosion. This statement
is supported by large volume of data on
radiocarbon dating that indicate that the
completion of the ice complex sediments
accumulation took place at the very end of
the late Pleistocene [Ivanov, 1981, Kaplina,
1981].
The materials presented above support
the statement that during Holocene, the
transformation of the ice complex sediments
was affected by multidirectional processes
[Shur, 1984].
Within the entire territory, thawing of the ice
complex was occurring not in the frontal, but
in the horizontal direction (laterally) when
masses of the ice complex were subject to
thermal abrasion of lakes and to thermal
denudation from the sides.
During the inundation period at the end of
the late Pleistocene and in the Holocene,
conditions of apical surfaces of the ice
complex remnants made possible the
preservation and the enhancement of their
stability.
As early as in 1940 [Efimov, Grave, 1940], the
idea emerged that a protection layer exists
which is located below the STL and above
the layer of buried ice or, according to the
modern theory, above the surface of the
Pleistocene singenetic polygonal-venous
ice. Under a thick forest in inter-alas surfaces
of Central Yakutia, this layer exists in a
permanently frozen state and does not thaw.
Soon after forest removal, the thickness of
the STL increases by 30-40 % (at an average
initial value of 1,3-1,4 m) and the protective
layer begins to thaw. The thickness of the
protective layer is 1,5 to 2 m.
This highly important conclusion has been
fully supported by further observations. In
the coastal lowlands, the protective layer is
also broadly developed on the remnants of
the ice complex. Some authors call this layer
the "cover layer" [Kaplina, 1981 ], while others
refer to this layer as to the "transient" layer
[Shur, 1984]
This layer is characterized by a very high ice
content (up to 60-70 %).The ice is represented
by ataxic and reticulate cryostructures. The
layer is composed of aleurolites and, in most
cases, 1,5 to 1,7 m deep.
Literature sources explain the genesis of
this layer from the two points of view. One
theory suggests that the cover layer is a
relic of the Holocene climatic maximum
when the depth of the seasonal thawing
in the ice complex remnants has increased
to approximately 2 m. Later, during cooling
in the late Holocene, part of this layer has
frozen from the bottom bringing the depth
of the STL to its current values, i. е., 40-50 cm
[Kaplina, 1981, 18].
Other authors conclude that during the
Holocene climatic optimum, such increase
in the depth of the STL was not possible
because a beginning of the inundation
process and the development of wetlands
in the coastal lowlands in the Holocene not
only did not coincide with the beginning of
warming, but had occurred in advance of the
warming. Indeed, irrefutable evidence exists
now that mass development of thermokarst
has begun not in the Holocene climatic
optimum, but substantially earlier, in the late
Pleistocene [Romanovskii, Gavriloy, Tumskoy,
et al., 1999]. In the remnants of the ice
complex (yedomas) hydrophilic vegetation,
including mosses and small shrubs,
expanded; peat-gleic soils have formed and
the STL soil water content has increased; all
these processes by no means promoted the
growth of the STL thickness.
In isolated and relatively rare cases, the
thickness of the cover layer in the ice complex
sequence somewhat exceeds average
values; at some sites, the cover layer forms
2,5-3 m deep moulds. This process was also
described by V.V. Kunitsky [2007] who used
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the term "bylar" to describe ice deposits that lie below the STL and associated their formation with the STL of higher water content compared to background values. A talik does not form in this case. Yu.L. Shur [1988] indicates that during Holocene, in places where inundation has not reached the extreme levels expressed by waterlogging of the territory and lakes formation, hydrophilic vegetation have developed promoting permafrost preservation. The inundation levels in the ice complex remnants varied; within small depressions, inundation level was somewhat higher leading to greater thickness of the cover layer.
In the past, for some period of time, a background depth of the STL in surfaces composed by the ice complex was greater than in the modern time. During the late Pleistocene, the Sartansk glacial sediment layers of the ice complex have formed. This theory was suggested by G.F. Gravis [1969] and further developed by Yu.L. Shur [1988] who based his analysis on the spore and pollen data of the ice complex sediments that indicate the prevalence of grassy vegetation and greater than modern depth of the seasonal thawing in open landscapes of the steppe-tundra.
Recent research activities confirm this point of view. Bio-geographic data on fossil insect associations in the ice complex sediments indicate the presence of multiple species of steppe beetles with strict requirements to the heat supply, in addition to boreal species of the northern tundra. During sea regression that has spread in the late glacial maximum to several hundreds of kilometers to the north of the modern shoreline, within exposed areas, continentality increase resulted in higher summer temperatures compared to the temperatures of the modern tundra. In the coastal lowlands to the west of the Kolyma river, July temperatures were 5-7°C higher and reached 11-12°C [Alfimov, Berman, 2004].
During the regression of the Arctic seas, the
polar day effect (i. e„ the thawing index equal
to the sum of summer air temperatures) increased substantially due to a substantial cloud cover decrease (at the present time, the cloud cover is 65-70%) which enhanced the thermal impact of direct solar radiation.
As a result, the thickness of the STL grew substantially with a significant decrease in the average annual soil temperatures due to a strong cooling effect of polar nights when air temperatures were dropping to -70°C. Therefore, summer temperatures did not prevent but, on the contrary, promoted the spread of thermophilic ecosystems beyond the boundaries of the modern land area of the shelf zone providing sustenance (food) for mammoth fauna.
Burrows of fossil rodents may serve as another indicator of the depth of the STL during accumulation of the ice complex sediments [Gubin, Zanina, Maksimovich, Kuzmina, Zazhigin, 2003]. The thickness of this layer during accumulation of the Karginsky ice complex sediments is 80-85 cm (sedimentary outcroppings of Duvannyi Yar, lower course of the Kolyma river) and 60-65 cm (sedimentary outcroppings at Zelenyi Mys, lower course of the Kolyma river). During Sartansk period, when continentality reached its maximum, the thawing index also reached its maximal values and the thickness of the STL has increased to at least 1 m.
After the completion of the accumulation of the sediments of the ice complexes and during its further presence in the Holocene time and as a result of changes in landscape characteristics (an increase in moisture content, development of moss cover, etc.) within non-thawed sites, the STL depths decreased followed by the rise of the upper surface of permafrost and formation of the ice-rich transient layer [Shur, 1988]. The process of formation of this transient layer is similar to a process, known as a "quasi-syngenesis process" in the literature [Kudryavtsev, 1978; Shur, 1988].
However, this process is not the only
process that determines the formation of
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Figure 3. Schematic representation of the transient layer formation during cyclic freezing-thawing.
Laboratory experiments with kaolin clay [8]; initial moisture content - 38%, mass volume - 1,3 g/см3,
I - V - cryogenic structures (black color) during freezing-thawing cycles.
v T H W , v sif - position of the thawing front and segregation ice formation
the cryogenic structure and the size of the
intermediate layer.
Water migration from the STL to the underly
ing upper horizon of permafrost is also of a
major significance. Water migration occurs
during summer seasons when the active
layer frozen during winter months, thaws and
a temperature gradient between its thawed
part and still frozen underlying permafrost
appears. This process is relatively well stud
ied in laboratory experiments and in field
observations [Parmuzina, 1978; Ershov, 1979,
Konstantinov, 1991, Solomatin, 1994]. The
field studies demonstrate that permafrost
water content may increase by a factor of
two reaching 50 % and higher as a result of
the downward migration of water from the
STL to the permafrost upper horizon. N.N. Ro
manovsky [1993] indicates that the migration
from the STL to the underlying frozen soils is
occurring within the range of average annual
temperatures (tov) of the frozen soils is equal
to -2 ~ -3°C to -8 ~ -10°C At tav close to 0°C
and due to small gradients, and at tav below
-10 ~ -12°C due to a low unfrozen water con
tent, this process is substantially weakened.
The significance of water migration process
to the transient layer that underlies the STL
becomes apparent from the comparison of
the data on numerous boreholes and out
croppings of the transient layer (1,5-1,7 m
on average) and the depths of the STL during
final phases of the ice complex accumulation
(approximately 1,0 m). Water was migrating
not only to the transient layer (which thick-
ness does not exceed 0,4-0,6 m), but to the
lower horizons as well.
The cryolithological composition of the ice-
rich transient layer of dark-gray or blue-gray
color significantly differs from the underlying
Sartansk horizon of the ice complex brown
in color and with massive and micro- fine
schliere cryogenic texture.
The frozen soil temperatures (tav) during
the formation of the layer composed of
brown aleurilites was very low, from -22 to
-33°C; summer temperatures of the upper
permafrost horizons did not exceed 10°C
[Konishchev, 2002]. This condition prohib
ited the migration of water from the STL to
the underlying frozen soils. Water migration
became possible either during the Holocene
or during one of the phases of warming at
the very end of the Pleistocene (Alleroed,
Boiling) when average annual and sum
mer temperatures increased sharply (tav =
= -8 ~ -14°C). Observations in other region
of the cryolithozone demonstrate that at the
present time, water is also migrating form
-
the STL to the underlying horizons of the
frozen soils [Chizov, Derevyagin, Mayer, 2005;
Konstantinov, 1991].
The formation of the transient layer as a
result of a transition of a part of the STL to
the permanently frozen state is, therefore,
complicated by water migration from the
STL to the underlying frozen layer.The overall
result is the increase in the ice content at the
surface of the remnants of the ice complex.
This process, together with the decrease in
the depth of the STL during the transition
from the upper Pleistocene to the Holocene,
may be interpreted as the aggradational
process that took place in parallel to the
degradational processes, i. e. an increase in
the area of alas depressions due to the ice
complex thermal abrasion, thawing of the
frozen horizons under lakes, etc. The ice-
rich transient or the "cover" layer is strongly
developed on the surface of the ice complex
and contemporaneously plays an important
protective role to external, first of all, thermal
impacts resulting from climate warming.
In the context of this analysis, the ice-rich
horizon of the upper permafrost horizon
could logically be called not a cover or
transient layer, but a protective layer, i. е., the
term that was initially suggested [Efimov,
Grave, 1940] could be used.
Thus, the destructive role of the Holocene
warming and the thermokarst erosion
modification of the ice complex sediments
represent only one type of reaction of the
cryolithozone to climate warming.The other
type of reaction are stabilizing changes in
landscape characteristics, e. g. the increase in
the moisture content of soils, development of
hydrophilic moss vegetation, accumulation
of organic matter in top soils, etc.
The presence of the protective layer provided
for the preservation of a significant part
of the ice complex during for more that
10 thousand years and it, in many ways,
determined modern landscape-permafrost
and geo-ecological conditions within a
large territory of East Siberia. Without this
protective layer, thermal abrasive and
thermal denudation processes could have
been many fold more intense, which can
be currently observed along the shoreline
of the Laptev and East Siberian seas where
the sea-banks composed of the ice complex
are intensively destructed by the sea thermal
abrasion and are retreating at a speed of
more that 10 cm per year.
At the present time, alases of Central Yakutia
are developing very slowly. The leading role
in the development of the thermokarst relief
belongs to anthropogenic activities [Bosikov,
1978].
Reliable data on somewhat significant
thermokarst processes in natural, intact by
human activities, ecosystems within inter
alas surfaces of Central Yakutia and the
apical surfaces of the ice complex remnants
in the Primorsky and the Northern Yakutia
resulting from the contemporaneous
climate change are absent. When surface
conditions are disturbed due to forest fires,
transport, forest logging, or agricultural
development in the area and within
surfaces composed of the ice complex
sediments, the depth of the STL increases
together with sagging, linear erosion and
other destructive processes that indicate
degradation of the permafrost complex.
Such reports often appear in the literature
[Gavriliev, Ugarov, 2008].
CONCLUSION
The response of the most important
characteristics of the cryolithozone to climate
warming depends upon the entire complex
of parameters of changing landscape and its
components that follow climate change.
The cryolithozone climate parameters
do not always directly correspond to the
parameters of atmospheric climate. The "soil-
ground" climate is determined by landscape
conditions where atmospheric climate
represents only one of the components.
Within some types of the permafrost
landscapes under climate warming,
-
protective reactions develop as a result
of negative feedbacks that stabilize some
permafrost characteristics (for example,
the depth of the seasonal thawing) or
even lead to a decrease in average annual
temperatures of the permafrost layer (tav), increase in the ice content of the upper
horizons of permafrost, and formation of
the ice-rich protective layer that mitigate
both inter-annual and multi-annual
variations in the depth of the STL. Under
climate warming, permafrost aggradational
changes (a decrease or stabilization of the
depth of the STL, decrease or stabilization of
t av in subordinate landscapes, and increase in ice content of the upper permafrost
horizons) are observed together with
degradation processes (increase in tav in autonomous landscapes, increase in the
area of taliks, etc.)
A response of permafrost to climate
change differs in principal within different
temperature and cryolithological types of
the cryolithozone, i. е., within the spread
of island and massive-island permafrost
represented predominantly by peatlands
on one hand, and within the spread of
discontinues permafrost where inter-fluvial
landscapes composed of mineral soils
(autonomous) alternate with waterlogged
subordinate landscapes of depressions
and river valleys (floodplains), on the other
hand.
The ambiguous response of permafrost
characteristics to climate warming is
observed both within the context of the
recent decades and of the longer time
intervals, specifically, during the period of
the upper Pleistocene - Holocene.
The integrity of the ice complex sediments
very unstable to thermal impacts, represents
a typical relict of the late Pleistocene cryochron
and is a consequence of the impact of
several permafrost processes that have led
to the formation of the protective layer at
the ice complex remnants in response to the
Holocene warming.
The discussion presented above supports
the need for further research based on
detailed monitoring in different regions
of the cryolithozone of Russia and other
countries. •
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Konischev, Vyacheslav Nikolaevich, was born in Moscow, in 1938. In 1960, he graduated from the Department of Polar Countries (renamed in 1967 to the Department of Cryolithology and Glaciology) of the Geography Faculty of M.V. Lomonosov Moscow State University. He received the Doctor of Science in Geography degree in 1978 and became a full Professor in 1981. He was awarded the title of Honored Worker of Science of the Russian Federation in 1999.
Professor Konischev has served as the Chair of the Department of Cryolithology and Glaciology since 1993. The areas of his scientific and teaching activities include permafrost science, cryolithology (composition and structure of cryolithic zone), and history and geo-ecology of Earth cryosphere. He has participated in scientific field expeditions in different regions of Northern Eurasia and Northern America; delivered lectures in universities of Canada, Iceland, Poland, China, and Japan; and published nine monographs and textbooks, and over 200 papers in peer-reviewed journals and proceedings.