Antarctic subglacial hydrology - interactions of subglacial lakes, basal water flow and ice dynamics

The Antarctic Ice Sheet influences the global temperature and sea level by complex interactions with the atmosphere and the ocean and is thus an important factor in the Earth's climate system. Recent climate assessments reveal a steady increase of global temperatures and an on-going shrinking of glaciers and ice sheets. Because the total Antarctic ice volume has the potential to raise the global sea level by about 58 meters, it is of particular interest to understand the ice dynamics regarding the mass export and thus the contribution to sea level rise. Observations of the last decades reveal a widespread hydrological system of subglacial lakes and drainage networks beneath the Antarctic Ice Sheet which is recognized to have a large impact on the ice dynamics. The aim of this thesis is to investigate this subglacial hydrological environment and its interactions with the ice flow dynamics of the overlying ice sheet. For reaching this aim, the ice flow model RIMBAY is enhanced by a subglacial hydrology module which provides the simulation of basal water flow and the identification of positions and extents of subglacial lakes. This model is then applied to the Antarctic Ice Sheet. A subsequent validation by the analysis of ice-penetrating radar profiles in Dronning Maud Land leads to the identification of 31 new potential subglacial lake locations. Based on these findings, the total number of Antarctic subglacial lakes is estimated to be 1300±300, a factor of three more than what has been discovered so far. Their overall extent is assessed to cover about 0.6% of the Antarctic ice-bed interface. Furthermore, strong correlations are found between modeled pathways of basal water flow and observed locations of ice streams. In a detailed investigation of the Ross Ice Streams at the Antarctic Siple Coast the local basal driver of fast ice flow is identified as water saturated and unconsolidated sediment. The assessment of the basal flow regime enables the simulation of basal drainage patterns which are clearly associated with current patterns of fast ice flow. The application of satellite-observed ice surface elevation changes to the present-day ice sheet geometry additionally allows prognostic water flow simulations. They reveal a high dynamic of basal water pathways. In particular, a major hydraulic tributary of the Kamb and Whillans Ice Stream is redirected towards the Bindschadler Ice Stream within the next 200 years, possibly resulting in future increase of ice velocities within the Bindschadler Ice Stream. In order to gain further insights into the complex feedback mechanisms between an ice sheet and its subglacial environment, ice dynamics and subglacial hydrology are modeled in a coupled approach for a synthetic domain. A new hydrological concept is developed and implemented in RIMBAY, providing the dynamic generation of subglacial lakes and covering the spatial and temporal variability of basal drainage systems. The impact of basal hydrology on the ice dynamic is estimated in various experiments, considering distinct feedback mechanisms. It is demonstrated, that a coupling at full complexity leads to a considerably negative mass balance of the investigated synthetic ice sheet. The results reveal the capabilities of the new hydrological concept and emphasize the necessity to incorporate subglacial hydrology in ice sheet models