would require not only a massive deglaciation of Greenland
and Western Antarctica but also a moderate loss of ice in
East Antarctica. Because the orbital parameters were close to
those of today, this interglacial is often considered to be one
of the best analogues of the present time.
Stage 6: Saale glaciation
The penultimate ice age, called Saale glaciation in Eurasia,
reached its maximum about 140,000 years ago. The Eurasian ice sheet covered a large part of Eastern Europe,
Russia and Siberia, practically equivalent to the maximum
expansion during the Quaternary in these regions (Svendsen
et al. 2004). The cooling causing the development of this cap
must have been much greater than during the LGM. Its
expansion towards the south is particularly impressive
because one of its lobes (the Diepner lobe, probably a
transitory phenomenon) came within 500 km of the Black
Sea. It appears in the southeast, that signs of maximum
extension are found even further south than for the Saale
glaciation, but it is difficult to know if these correspond to
the same ice sheet and what its age might be (see Fig. 24.6).
Scenario of the Last Glacial-Interglacial Cycle
The temporal pattern of the last glacial-interglacial cycle is
shown in Fig. 24.3. The external forcing associated with
variations in the Earth’s orbit is represented by the evolution
of summer insolation at 65 °N latitude. The sea level indicates the overall volume of ice.
It is clear that the volume of ice reacts systematically to
variations in summer insolation. As it is mainly the summer
climate that is responsible for the ablation, an orbital configuration with strong summer insolation is unfavorable to
the ice sheets. In addition, the slow freeze-ups and the rapid
deglaciations are not symmetrical. The volume over the
whole cycle is a sawtooth trend because the retreats are not
complete and each advance (around 120, 90, 80, 60 and
40 ka BP) resumes from a still glaciated situation, even more
so as the Ice Age progresses.
However, the geographical distribution reveals great
diversity (the geographical aspects are summarized in
Fig. 24.6 for Fennoscandia and 2.7 for Laurentide).
During the Eemian (125 ka BP), the eustatic sea level
was up to 6 m higher than currently, testifying to a strong
retreat of the ice. The southern part of Greenland and
Western Antarctica were probably much less ice-covered
than they are at present. However, ice core drilling indicates
that there was an ice cap in the central part of Greenland at
an altitude comparable to the current altitude (NGRIP
Members 2004).
The Laurentide Ice Sheet
The Laurentide ice sheet over North America was the first to
form, with ice appearing on the heights in the form of two
separate caps, one over Keewatin (itself derived from the
junction of the Keewatin and Baffin caps) and the other on
Labrador (Fig. 24.7). Throughout the ice age, it underwent
fluctuations, with the two caps joining during the colder
periods followed by growth (both in volume and area) of the
resulting ice sheet, generally with two distinct domes.
Conversely, during interstadials (warmer intervals during
the glaciation) it shrank and in some cases separated into two
(or even three) ice sheets. Another ice cap also developed on
the Rocky Mountains, the Cordilleran ice sheet, but it took
at least 60 ka BP before there was a junction between the
Laurentide sheet and the still undeveloped Cordilleran sheet.
The Cordilleran ice sheet only became heavily glaciated at a
late stage (after 30 ka BP). This phenomenon was attributed
to the influence of the Laurentide on atmospheric circulation.
The Laurentide needed to be high enough to affect the jet
stream, which had the effect of increasing the transport of
moisture to the Cordillera.
It should be noted that despite fluctuations, a significant
amount of ice persisted over North America throughout the
ice age.
During the Last Glacial Maximum (21 ka BP), the area
covered is shown in Fig. 24.1. During the deglaciation, the
retreat of the Laurentide accelerated from 15 ka
BP. A proglacial lake (Lake Agassiz) was formed south of
the ice sheet. It emptied around 8200 years by breaking its
ice dam and rapidly injected a large quantity of fresh water
into the North Atlantic, with repercussions on the thermohaline circulation. The deglaciation in North America continued up to 6 ka BP.
The Fennoscandian Ice Sheet
Ice appeared later on Eurasia and initially in a limited way
on the Arctic archipelagos (Svalbard, François Joseph) and
on the mountains of Scandinavia. It was only towards 90 ka
BP that a major glaciation appeared in Western Siberia.
Then, during each cold period a large sheet developed with a
junction between the Svalbard archipelago, northern Scandinavia and New Zemble (Barents and Kara seas). During
each interstadial, the Barents and Kara seas were free of ice
and often ice only remained in arctic archipelagos and on
high points in Scandinavia (Svendsen et al. 2004). This
behavior, which suggests a strong sensitivity to the climate,
can be explained by several positive feedbacks:
– the terrestrial part (lying on a bedrock above sea level)
was more limited in area and thickness than the Laurentide. As a result, it is more subject to the
24 The Cryosphere and Sea Level
313
and Western Antarctica but also a moderate loss of ice in
East Antarctica. Because the orbital parameters were close to
those of today, this interglacial is often considered to be one
of the best analogues of the present time.
Stage 6: Saale glaciation
The penultimate ice age, called Saale glaciation in Eurasia,
reached its maximum about 140,000 years ago. The Eurasian ice sheet covered a large part of Eastern Europe,
Russia and Siberia, practically equivalent to the maximum
expansion during the Quaternary in these regions (Svendsen
et al. 2004). The cooling causing the development of this cap
must have been much greater than during the LGM. Its
expansion towards the south is particularly impressive
because one of its lobes (the Diepner lobe, probably a
transitory phenomenon) came within 500 km of the Black
Sea. It appears in the southeast, that signs of maximum
extension are found even further south than for the Saale
glaciation, but it is difficult to know if these correspond to
the same ice sheet and what its age might be (see Fig. 24.6).
Scenario of the Last Glacial-Interglacial Cycle
The temporal pattern of the last glacial-interglacial cycle is
shown in Fig. 24.3. The external forcing associated with
variations in the Earth’s orbit is represented by the evolution
of summer insolation at 65 °N latitude. The sea level indicates the overall volume of ice.
It is clear that the volume of ice reacts systematically to
variations in summer insolation. As it is mainly the summer
climate that is responsible for the ablation, an orbital configuration with strong summer insolation is unfavorable to
the ice sheets. In addition, the slow freeze-ups and the rapid
deglaciations are not symmetrical. The volume over the
whole cycle is a sawtooth trend because the retreats are not
complete and each advance (around 120, 90, 80, 60 and
40 ka BP) resumes from a still glaciated situation, even more
so as the Ice Age progresses.
However, the geographical distribution reveals great
diversity (the geographical aspects are summarized in
Fig. 24.6 for Fennoscandia and 2.7 for Laurentide).
During the Eemian (125 ka BP), the eustatic sea level
was up to 6 m higher than currently, testifying to a strong
retreat of the ice. The southern part of Greenland and
Western Antarctica were probably much less ice-covered
than they are at present. However, ice core drilling indicates
that there was an ice cap in the central part of Greenland at
an altitude comparable to the current altitude (NGRIP
Members 2004).
The Laurentide Ice Sheet
The Laurentide ice sheet over North America was the first to
form, with ice appearing on the heights in the form of two
separate caps, one over Keewatin (itself derived from the
junction of the Keewatin and Baffin caps) and the other on
Labrador (Fig. 24.7). Throughout the ice age, it underwent
fluctuations, with the two caps joining during the colder
periods followed by growth (both in volume and area) of the
resulting ice sheet, generally with two distinct domes.
Conversely, during interstadials (warmer intervals during
the glaciation) it shrank and in some cases separated into two
(or even three) ice sheets. Another ice cap also developed on
the Rocky Mountains, the Cordilleran ice sheet, but it took
at least 60 ka BP before there was a junction between the
Laurentide sheet and the still undeveloped Cordilleran sheet.
The Cordilleran ice sheet only became heavily glaciated at a
late stage (after 30 ka BP). This phenomenon was attributed
to the influence of the Laurentide on atmospheric circulation.
The Laurentide needed to be high enough to affect the jet
stream, which had the effect of increasing the transport of
moisture to the Cordillera.
It should be noted that despite fluctuations, a significant
amount of ice persisted over North America throughout the
ice age.
During the Last Glacial Maximum (21 ka BP), the area
covered is shown in Fig. 24.1. During the deglaciation, the
retreat of the Laurentide accelerated from 15 ka
BP. A proglacial lake (Lake Agassiz) was formed south of
the ice sheet. It emptied around 8200 years by breaking its
ice dam and rapidly injected a large quantity of fresh water
into the North Atlantic, with repercussions on the thermohaline circulation. The deglaciation in North America continued up to 6 ka BP.
The Fennoscandian Ice Sheet
Ice appeared later on Eurasia and initially in a limited way
on the Arctic archipelagos (Svalbard, François Joseph) and
on the mountains of Scandinavia. It was only towards 90 ka
BP that a major glaciation appeared in Western Siberia.
Then, during each cold period a large sheet developed with a
junction between the Svalbard archipelago, northern Scandinavia and New Zemble (Barents and Kara seas). During
each interstadial, the Barents and Kara seas were free of ice
and often ice only remained in arctic archipelagos and on
high points in Scandinavia (Svendsen et al. 2004). This
behavior, which suggests a strong sensitivity to the climate,
can be explained by several positive feedbacks:
– the terrestrial part (lying on a bedrock above sea level)
was more limited in area and thickness than the Laurentide. As a result, it is more subject to the
24 The Cryosphere and Sea Level
313