Some Views on the Water Level in Lake Malaren and in the Adjacent Baltic Sea

Abstract

The global temperature during the last century has risen about 0,5° C and the Ocean water level about 7-8 cm. The change-which is considered linear with temperature-is thus 15 cm per degree. From rather reliable estimates of the global temperature during past ages and the obtained quantitative relation between eustatic changes and temperature we have estimated the eustatic change during the last thousand years to be of the order of + 10 cm. Several earlier estimates of much larger eustatic changes made by geologists and archaeologists in the Stockholm region are discussed and tentative explanations for their differing results are presented based mainly on meteorological, hydrological and oceanographic considerations. Some comments are also given concerning assumed eustatic changes during a time several thousand years ago. The average water level in Lake Malaren during its transforma- tion from a bay in the Baltic to a secluded lake is depending on the changes of the water level in the Baltic and is thus decreasing with time in relation to a fix point on land. A difference between the average water levels in Malaren and the Baltic has always existed although it was very small thousand years ago. The difference has since been slowly and smoothly increasing with time up to about 25 cm in the beginning of this century, whereas in individual years the yearly average differ- ence has varied considerably. Large variations in the water levels occur during short periods both in the Baltic and in Malaren. Such extreme values should not be interpreted as representing secular average values.