Greenland englacial drainage: conditions favoring water transport through a fractured aquifer

Abstract:

Recently, the subglacial hydrology of glaciers and ice sheets has garnered intense interest because of its effects on ice sliding and potential ice sheet responses leading to sea level rise. Less attention has focused on the englacial water system that connects surface meltwater sources to the basal drainage system. Observations of englacial drainage have revealed diametrically opposed behaviors, so that understanding the role of the englacial system is critical to developing knowledge of ice sheet responses. The englacial connections either enhance or limit subglacial processes, including sliding. Some observations show cases where water drainage is mainly through an englacial system of fractures so that water flow at the bed is stunted. Other observations show static englacial water systems that play little role in drainage with primary drainage routes being along the bed. Here, we use a thermomechanical model of englacial water flow to understand the interaction between ice and water along these connections. We assume that water flow is through a series of connected fractures analogous to crevassed Greenland outlet glaciers. The fractures are modified by ice flow, and freezing and melting of the water system. Simple mathematical analyses show trade offs between closure rates and melting rates that determine the englacial flowpaths. From numerical experiments, we show that the dominance of englacial flow follows the locations of both bed overdeepenings and areas where the basal water system is compressed dynamically. The preponderance of overdeependenings in Greenland suggests that englacial systems may be favored in critical areas of ice sheet flow. We conclude by relating the insights from the analytic and numerical results to the broad scale patterns of change of the Greenland Ice Sheet.