ScienceDaily (Dec. 30, 2008) — According to a new doctoral
dissertation at Stockholm University in Sweden, based on analyses of
deposits of pollen grains, it is possible that all of Sweden was
virtually free of ice for long periods during the latest ice age. The
findings show that the glaciation might have started some 20,000 later
than was previously assumed.
“It’s important that we get to the bottom of when the great ice sheets
covered Sweden and how warm it might have been when there was no ice.
At present there are two extremely different hypotheses, which makes
it difficult to study how the ice age climate relates to various
parameters in the climate system, such as the earth’s relation to the
sun,” says Martina Hättestrand, a doctoral candidate at the Department
of Physical Geography and Quaternary Geology, Stockholm University.
In order to understand the climate system of the earth, researchers
today are studying the climatic variations of ice ages. Since we have
the most land forms and geological traces preserved from the latest
ice age, much of the research focuses on that particular period. An
important aspect of the research is to study when the huge continental
ice sheets grew and when they melted away, and to study the
environment and climate of the areas that were free of ice. The size
and movement patterns of the ice sheets can be calculated by studying
land forms and moraine deposits. The ice-free periods can be studied
by pollen analysis, among other methods. Pollen analysis is a method
in which scientists use pollen grains preserved in ancient sediment to
create a picture of what plants once grew in the area and what the
climate was like.
Martina Hättestrand’s dissertation is based on studies of pollen
grains that were deposited more than 40,000 years ago in small lakes
during the ice-free phases of the latest glaciation. During the warm
phases of the Ice Age, high amounts of birch pollen were deposited,
which indicates that summer temperatures were around 10 degrees
centigrade in northern Sweden. During cold ice-free phases, mostly
grass and herbal pollen was deposited.
“The findings from my dissertation indicate that the first icing up
phase of the latest Ice Age may in Scandinavia have started about
95,000 years ago – which is some 20,000 years later than was
previously thought,” says Martina Hättestrand.
According to the previously accepted hypothesis, Sweden was covered
with ice 75,000-20,000 years ago. Martina Hättestrand’s hypothesis, on
the other hand, is that Sweden may have largely been ice-free between
59,000 and 40,000 years ago. If this is true, the last ice sheet of
the Ice Age formed much more rapidly than was previously believed in
order to have reached all the way down to northern Germany during the
maximum phase about 22,000 years ago.
The latest Ice Age is called the Weichselian glacial (glaciation) in
northern Europe. It started roughly 120,000 years ago and ended about
10,000 years ago. The definition of an ice age is that it has a colder
climate than an interglacial period, which is the type of climate we
live in today. The climate varied a great deal during the ice ages.
Adapted from materials provided by Vetenskapsrådet (The Swedish
Research Council), via AlphaGalileo.
APA
MLA
Vetenskapsrådet (The Swedish Research Council) (2008, December 30).
Pollen Grain Study Yields New Picture Of Ice Age. ScienceDaily.
Retrieved December 30, 2008, from http://www.sciencedaily.com /
releases/2008/12/081222113522.htm
and
Disputation 24 oktober Martina Hättestrand, Vegetation and climate
during Weichselian ice free intervals in northern Sweden
De Geer lecture hall 13.00 - 15.00
Abstract:
In this thesis the Weichselian history of northern Sweden is
investigated, with emphasis on vegetation and climate during ice-free
intervals. The main method used has been pollen analysis of sediments
from pre-Late Weichselian landforms. To interpret fossil pollen
assemblages, comparisons with modern pollen spectra were made. Modern
pollen data were retrieved through monitoring of annual pollen
deposition at seven sites in northern Sweden, from the boreal forest
to above the present forest-line of birch. Eight years of pollen
monitoring is described and put in a larger context through comparison
with monitoring data from Iceland, Svalbard, Norway and Finland. A
study of sediment cores from the Riipiharju esker shows evidence of
two ice free phases during the Weichselian glacial; Tärendö I and
Tärendö II. The Tärendö II ice free interval includes large climatic
shifts, previously not recognized, from relatively warm conditions
with Betula as the dominating pollen taxon to cold conditions with
dominance of Artemisia and Gramineae and back to warmer conditions
again. Correlation alternatives of the north Swedish ice free
intervals Tärendö I and II are: 1/ Brörup (MIS 5c; c. 105-93 ka BP)
and Odderade (MIS 5a; c. 85-74 ka BP), respectively, or 2/ Odderade
and early Middle Weichselian time (MIS 3; c. 59-40 ka BP). Of these,
alternative 2 is regarded as the most likely. Interstadial sediments
deposited in a Veiki moraine plateau during downwasting of a pre-Late
Weichselian ice sheet include only Betula dominant pollen spectra,
showing that the climate during formation of the Veiki moraine was
relatively warm. According to stratigraphical correlation there are
three possible alternatives for Veiki moraine formation. Either it was
formed during 1/ early Tärendö I, 2/ early Tärendö II, or 3/ late
Tärendö II. Alternative 3 implies growth of an intermediate ice sheet
reaching the eastern limit of Veiki moraine distribution during the
cold phase of Tärendö II.
http://www.sciencedaily.com/releases/2008/12/081222113522.htm
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