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.

Source: ScienceDaily (30 December 2008)