496
Land·Ocean Systems in the Siberian Arctic: Dynamics and History
ice-rich permafrost, slight drainage and low relief energy. The calculated increase of the active
layer depth during the Holocene climatic optimum was between 0.5 to 1.0 m on the watersheds
and 0.2 to 0.4 m in depressions (Derevyagin et ai, 1996). The cryostructures of permafrost
lying below investigated Holocene lacustrine deposits suggest that the thickness of sub-lake
taliks rose to maximum values of about 2 m. The near-surface location of Pleistocene polygonal
ice wedges and the conservation of large buried glacier ice bodies confirm this result. Polygonal
ice wedge systems also continue to grow in flat wet areas of the Labaz region at the present
time. Nonetheless, their stable isotope ratio ranges from -15.8 %0 to -23.3 %0 and from -117 %0
to -165 %0 for 0 18 0 and 02H, respectively.
Conclusion
The landscape evolution in the Labaz Lake area during early post-Zyryan times was primarily
dominated by processes connected with the decay of the ZyryanlEarly Weichselian ice cover.
The character of these processes was strongly influenced by the specific peculiarities of glacier
ice thawing in a territory with underlying continuous, low-temperature permafrost. Climate
fluctuations in post-Zyryan times have led to a varying intensity of ice decay, denudation, and
accumulation. Complicated thermokarst and thermoerosional processes have taken place. The
most intensive glacial ice decay seems to have occurred during the first warming stage of the
Kargin/Middle Weichselian Interstadial before more than 40000 yr BP. The formation of
extensive lake depressions within the glacial deposits and the accumulation of sediments which
built the widespread lacustrine 60 m terrace seems to be connected with these times.
A surface stabilization occurred about 40000 yr BP, probably caused by a cooler and more
continental climate. Glacier ice disintegration was slowed and large flat areas of lacustrine
sediments became subaerially exposed. As a consequence, deposits with thick polygonal ice
wedges (Ice Complex) and peat beds could be formed. Subsequent warming phases, apparently
connected with an increase of precipitation, led to a new activation of thermokarst and glacier
ice decay, and to the accumulation of the second horizon of Kargin lacustrine and fluviolacustrine sediments. Glacier ice was buried progressively deeper by ablation deposits.
Although the paleoenvironmental data in general suggest strong continental climatic
conditions, we have not obtained evidence permitting a decision on the existence of a vast icedammed lake ,Pre-Labaz' during the Sartan period, as supposed by Isaeva (1982). Occurrence
of lacustrine sediments dated around 17000 yr BP at an altitude of more than 80 m at the
Kokora Lake argue for this concept. If we assume that the loess-like silts in the section LA06
also relate to the Sartan time, then we have a second indicator for the existence of lakes during
this time in the Labaz Lake area.
The pollen assemblages from the investigated post-Zyryan sediment profiles indicate a
continuous tundra vegetation. From the presence of significant amounts of shrub pollen and
especially larch throughout the documented time interval, sufficiently high summer
temperatures are evidenced not only during the Kargin Interstadial period, but also during the
Sartan Glacial. In this context, the ,cold, stable isotope signature of the studied Late Pleistocene
ice wedges suggests a strong continental climate, characterized by relative warm summer and
very low winter temperatures.
Altogether, it is most probable that after 17-15000 yr BP lacustrine sedimentation was
interrupted in wide areas. Wide spread polygonal ice-wedges, partially with signs of epigenetic
growth in lacustrine sediments, support such an assumption. Lacustrine sediments formed
during reactivation of lacustrine sedimentation after the drying of lake depressions were dated
between 14400 and 11800 yr BP and likely belong to the late glacial warming events BI/llling
and Allerl/ld. To achieve a clarification of this problem, the use of other dating methods in
Land·Ocean Systems in the Siberian Arctic: Dynamics and History
ice-rich permafrost, slight drainage and low relief energy. The calculated increase of the active
layer depth during the Holocene climatic optimum was between 0.5 to 1.0 m on the watersheds
and 0.2 to 0.4 m in depressions (Derevyagin et ai, 1996). The cryostructures of permafrost
lying below investigated Holocene lacustrine deposits suggest that the thickness of sub-lake
taliks rose to maximum values of about 2 m. The near-surface location of Pleistocene polygonal
ice wedges and the conservation of large buried glacier ice bodies confirm this result. Polygonal
ice wedge systems also continue to grow in flat wet areas of the Labaz region at the present
time. Nonetheless, their stable isotope ratio ranges from -15.8 %0 to -23.3 %0 and from -117 %0
to -165 %0 for 0 18 0 and 02H, respectively.
Conclusion
The landscape evolution in the Labaz Lake area during early post-Zyryan times was primarily
dominated by processes connected with the decay of the ZyryanlEarly Weichselian ice cover.
The character of these processes was strongly influenced by the specific peculiarities of glacier
ice thawing in a territory with underlying continuous, low-temperature permafrost. Climate
fluctuations in post-Zyryan times have led to a varying intensity of ice decay, denudation, and
accumulation. Complicated thermokarst and thermoerosional processes have taken place. The
most intensive glacial ice decay seems to have occurred during the first warming stage of the
Kargin/Middle Weichselian Interstadial before more than 40000 yr BP. The formation of
extensive lake depressions within the glacial deposits and the accumulation of sediments which
built the widespread lacustrine 60 m terrace seems to be connected with these times.
A surface stabilization occurred about 40000 yr BP, probably caused by a cooler and more
continental climate. Glacier ice disintegration was slowed and large flat areas of lacustrine
sediments became subaerially exposed. As a consequence, deposits with thick polygonal ice
wedges (Ice Complex) and peat beds could be formed. Subsequent warming phases, apparently
connected with an increase of precipitation, led to a new activation of thermokarst and glacier
ice decay, and to the accumulation of the second horizon of Kargin lacustrine and fluviolacustrine sediments. Glacier ice was buried progressively deeper by ablation deposits.
Although the paleoenvironmental data in general suggest strong continental climatic
conditions, we have not obtained evidence permitting a decision on the existence of a vast icedammed lake ,Pre-Labaz' during the Sartan period, as supposed by Isaeva (1982). Occurrence
of lacustrine sediments dated around 17000 yr BP at an altitude of more than 80 m at the
Kokora Lake argue for this concept. If we assume that the loess-like silts in the section LA06
also relate to the Sartan time, then we have a second indicator for the existence of lakes during
this time in the Labaz Lake area.
The pollen assemblages from the investigated post-Zyryan sediment profiles indicate a
continuous tundra vegetation. From the presence of significant amounts of shrub pollen and
especially larch throughout the documented time interval, sufficiently high summer
temperatures are evidenced not only during the Kargin Interstadial period, but also during the
Sartan Glacial. In this context, the ,cold, stable isotope signature of the studied Late Pleistocene
ice wedges suggests a strong continental climate, characterized by relative warm summer and
very low winter temperatures.
Altogether, it is most probable that after 17-15000 yr BP lacustrine sedimentation was
interrupted in wide areas. Wide spread polygonal ice-wedges, partially with signs of epigenetic
growth in lacustrine sediments, support such an assumption. Lacustrine sediments formed
during reactivation of lacustrine sedimentation after the drying of lake depressions were dated
between 14400 and 11800 yr BP and likely belong to the late glacial warming events BI/llling
and Allerl/ld. To achieve a clarification of this problem, the use of other dating methods in