MELTWATER UNDER THE SCANDINAVIAN ICE SHEET: VOLUMES, DRAINAGE MECHANISMS AND CONSEQUENCES FOR ICE SHEET BEHAVIOUR

Meltwater under ice sheets originates primarily from melting of basal ice, recharge from the ice surface and recharge from subglacial groundwater systems. The relative importance of these processes depends on a combination of glaciological, climatological and hydrogeological parameters. Water at the ice/bed interface (IBI) is of crucial importance for ice sheet stability, movement mechanisms, sediment transfer and the production of specific landforms. Under slowly melting ice sheets resting on thick, permeable beds basal water will be escaping into the substratum. Such ice sheets are firmly coupled to their beds, move slowly, transfer little sediment and exert little geomorphic effect on their beds. The opposite situation, i.e. where water recharge at IBI exceeds the drainage capacity of the bed leads to a highly dynamic ice sheet characterized by weak basal coupling, efficient sediment re-distribution, production of fast-flow subglacial landforms and glaciotectonism. We synthesize results of numerical modelling of water flow through subglacial aquifers under the marginal part of the Scandinavian Ice Sheet in Poland, Germany and Denmark during several glacial cycles to illustrate that these aquifers lacked the capacity to evacuate meltwater from IBI. Meltwater typically accumulated under the ice sheet leading to ice streaming and the formation of specific landform/sediment assemblages created in subglacial cavities and channels before catastrophic drainage through tunnel valleys removed the surplus meltwater. The results confirm a distinct relationship between the hydrogeological properties of the substratum and ice sheet behaviour at both, local and regional scale.