The presence of an ice sheet can exert numerous influences on the ground beneath; the weight of the overlying ice can force isostatic adjustments, and meltwater at an ice sheet bed can affect groundwater flow, ice velocity and the potential for erosion of the substrate. Collecting data on ice temperature, ice velocities, hydrology, ice geometry and meteorological conditions contributes to improving knowledge of physical processes associated with glaciation. The above-mentioned variables can be explored in contemporary ice sheet and glacier settings, but in order to understand past glaciations proxy data from glacial geomorphology must be also be applied. In this report we discuss the analysis of glacial geomorphological data from the northern Stockholm Archipelago and the sea floor of the Gulf of Bothnia, in addition to temperature and geometry changes of contemporary Swedish glaciers.
Studies on a selection of glaciers in High Alpine Sweden reveal that though the temperature distribution adjusts to changes, the speed of change cannot match a quick recession as was recorded during the deglaciation of the Weichselian Ice Sheet. The ice remained cold in analogy with the present Greenlandic Ice Sheet. The colder Antarctic environment is more in analogy with the maximum phase of the Weichselian glaciation. Basal temperature conditions reflect long term changes and are thus more influenced by the maximum phase than by variations in climate during deglaciation. At a late stage of deglaciation, meltwater may have warmed up bed temperatures.
Mapping of bathymetric data provides evidence of significant subglacial water pathways and fast flowing ice along the east coast of Sweden, with further evidence for Baltic Ice Stream onset on the present day Ångermanland-Västerbotten coast during the Late Weichselian. The existence of a Baltic Ice Stream has been shown through modelling experiments to be a necessity to reproduce the Last Glacial Maximum extent in the Baltic sector of Scandinavian Ice Sheet, as inferred by the geomorphological record. However, we believe that an ice shelf or a frozen patch over Åland would be necessary to sufficiently reduce ice flow and thinning in this region, and prevent premature marginal retreat.
The geomorphological landform record, with an impressive array of meltwater channels and eskers of a multitude of spatial scales, suggests that meltwater was plentiful in the Baltic/Bothnian sector during deglaciation. A numerical model was thus used to simulate the Weichselian evolution of the ice sheet and its sensitivity to surface meltwater inputs. The proportion of basal sliding that can be attributed to surface meltwater-enhanced basal sliding varies over space and time, and results of ice sheet modelling highlight the difficulty of implementing the surface meltwater effect through simple parameterizations. This stresses the importance of continued development of physically-based models of surface-to-bed meltwater transfer, needed to better simulate the spatial and temporal variability of hydrology and dynamics, and their response to changes in climate and meltwater production, within ice sheet models.
The primary aim of this study was to improve our understanding of processes acting underneath an ice sheet, specifically during a deglaciation. Based on the results of studies on present day High Alpine glaciers, the Antarctic and Greenland ice sheets, and glacial geomorphological mapping from land and marine-based data in the Gulf of Bothnia, we have gained an insight into how future glaciations may affect the northeast coast of Uppland, eastern Sweden. Evidence of ice streaming over a large distance in the Gulf of Bothnia, including the presence of numerous glacial lineations of varying scale, contests to a period of fast basal sliding during the Late Weichselian deglaciation. This suggests that there would have been a degree of erosion at the ice sheet bed during this time.
The evidences for a Baltic Ice Stream are linked to the long term existence of the Gulf of Bothnia and the Baltic. Unfrozen soft sea bed sediments allowed a fast sliding speed at a stage of glacier advance and the bed remained wet all through the glaciation. Thus there are good reasons to assume that coming glaciations will act in a similar manner as the Weichselian glaciation did.
Stockholm, 2016. , 67 p.