638
Climatic Geomorphology
8. Climate fluctuations in periglacial regions during the late quaternary
Most of the periglacial regions are over permafrost. It disappears when summer warming
exceeds cooling in winter, and vice versa. At present, the periglacial environments occupy
25% of the Earth's surface and during the last glaciation could reach 20 to 25 per cent or
more (French, 1996).
Possibly, the most relevant criteria to estimate the periglacial area during the late
Quaternary are the distribution of plants and the extension of ecozones. All this implies
that there were tundra, steppe and forest fluctuations at this time. Therefore, palynological
research is crucial to these effects and has made possible to establish pollen regions and
climate periods (French, 1996). Also, faunal remains, such as molluscs and insects, help
with the interpretation of the environmental conditions. Nevertheless, the studies leading
to this are scarce.
Permafrost evolves very slowly with respect to warming and cooling stages. In the late
Pleistocene and Holocene the thaw of the ice sheets and the subsequent sea level rise are
processes much more rapid than the loss of thickness of the permafrost (Dawson, 1992).
For example, the permafrost in northeastern Siberia has always been present since the late
Pleistocene (Washburn, 1979).
The most detailed knowledge that exists on the climate and vegetation fluctuations that
have occurred during the late Quaternary exists in Europe. Btidel (1951) differentiated
three vegetation zones in Europe (tundra, steppe, and forest) and indicated that the
majority of the European surface to the south of the ice sheets was affected by periglacial
conditions, except for the southern Iberian Peninsula and the Mediterranean coasts.
Nevertheless, nowadays it is calculated that the extension of the periglacial band in central
and western Europe was about 50 km during the maximum of the last glaciation
(Weichselian). This width has been obtained mainly by the analysis of ice and sand
wedges and annular ramps of pingos. The most important climate record corresponds to
the pollen diagram of Grand Pile (Mook and Woillard, 1982), which shows the first stage
of the development of the permafrost was about 90,000 years ago. Later, other permafrost
periods, separated by warm interstadials, follow each other.
In European and Asiatic Russia an important increase of permafrost occurred during
the late Quaternary, reaching up to 700 m thick. The continuous permafrost was located
up to 50~ having in total a dimension of 400 to 600 km (Figure 24.18) (Baulin and
Danilova, 1984). The evolution of the permafrost is similar to that in Europe, with growing
periods that coincide with cool stages, alternating with warmer periods.
Several data sets reveal that in North America there was a relict permafrost
corresponding to the last glacial maximum (upper Wisconsinan), because for previous
periods the information is very scarce. The permafrost band to the south of the Laurentide
ice sheet is narrower than around the Euroasiatic ice sheet. This can be explained by a
faster advance of the Laurentide ice sheet toward more southern latitudes, and therefore,
areas with intense periglacial conditions are more limited than in Europe. In Figure 24.19
the areas of permafrost are indicated, together with the landforms related to fossil
permafrost and other inactive periglacial morphologies that do not require permafrost
conditions. On the other hand, at present the permafrost occurs under the 82% of the
surface of Alaska and northwestern Canada (P6w6, 1983). On the Alaskan coast, many
pingos corresponding to a closed system occur, whereas in central Alaska pingos of
Climatic Geomorphology
8. Climate fluctuations in periglacial regions during the late quaternary
Most of the periglacial regions are over permafrost. It disappears when summer warming
exceeds cooling in winter, and vice versa. At present, the periglacial environments occupy
25% of the Earth's surface and during the last glaciation could reach 20 to 25 per cent or
more (French, 1996).
Possibly, the most relevant criteria to estimate the periglacial area during the late
Quaternary are the distribution of plants and the extension of ecozones. All this implies
that there were tundra, steppe and forest fluctuations at this time. Therefore, palynological
research is crucial to these effects and has made possible to establish pollen regions and
climate periods (French, 1996). Also, faunal remains, such as molluscs and insects, help
with the interpretation of the environmental conditions. Nevertheless, the studies leading
to this are scarce.
Permafrost evolves very slowly with respect to warming and cooling stages. In the late
Pleistocene and Holocene the thaw of the ice sheets and the subsequent sea level rise are
processes much more rapid than the loss of thickness of the permafrost (Dawson, 1992).
For example, the permafrost in northeastern Siberia has always been present since the late
Pleistocene (Washburn, 1979).
The most detailed knowledge that exists on the climate and vegetation fluctuations that
have occurred during the late Quaternary exists in Europe. Btidel (1951) differentiated
three vegetation zones in Europe (tundra, steppe, and forest) and indicated that the
majority of the European surface to the south of the ice sheets was affected by periglacial
conditions, except for the southern Iberian Peninsula and the Mediterranean coasts.
Nevertheless, nowadays it is calculated that the extension of the periglacial band in central
and western Europe was about 50 km during the maximum of the last glaciation
(Weichselian). This width has been obtained mainly by the analysis of ice and sand
wedges and annular ramps of pingos. The most important climate record corresponds to
the pollen diagram of Grand Pile (Mook and Woillard, 1982), which shows the first stage
of the development of the permafrost was about 90,000 years ago. Later, other permafrost
periods, separated by warm interstadials, follow each other.
In European and Asiatic Russia an important increase of permafrost occurred during
the late Quaternary, reaching up to 700 m thick. The continuous permafrost was located
up to 50~ having in total a dimension of 400 to 600 km (Figure 24.18) (Baulin and
Danilova, 1984). The evolution of the permafrost is similar to that in Europe, with growing
periods that coincide with cool stages, alternating with warmer periods.
Several data sets reveal that in North America there was a relict permafrost
corresponding to the last glacial maximum (upper Wisconsinan), because for previous
periods the information is very scarce. The permafrost band to the south of the Laurentide
ice sheet is narrower than around the Euroasiatic ice sheet. This can be explained by a
faster advance of the Laurentide ice sheet toward more southern latitudes, and therefore,
areas with intense periglacial conditions are more limited than in Europe. In Figure 24.19
the areas of permafrost are indicated, together with the landforms related to fossil
permafrost and other inactive periglacial morphologies that do not require permafrost
conditions. On the other hand, at present the permafrost occurs under the 82% of the
surface of Alaska and northwestern Canada (P6w6, 1983). On the Alaskan coast, many
pingos corresponding to a closed system occur, whereas in central Alaska pingos of