The influence of a model subglacial lake on ice dynamics and internal layering

Abstract

Abstract.As ice flows over a subglacial lake, the drop in bed resistance leads to an increase in ice velocities and a draw down of isochrones and cold ice. The ice surface flattens as it adjusts to the lack of resisting forces at the base. The rapid transition in velocity induces changes in ice viscosity and releases deformation energy that can raise the temperature locally. Recent studies of Antarctic subglacial lakes indicate that many lakes experience very fast and possibly episodic drainage, during which the lake size is rapidly reduced as water flows out. Questions that arise are what effect this would have on internal layers within the ice and whether such past drainage events could be inferred from isochrone structures downstream.Here, we study the effect of a subglacial lake on ice dynamics as well as the influence that such short timescale drainage would have on the internal layers of the ice. To this end, we use a full Stokes, polythermal ice flow model. An enthalpy-gradient method is used to account for the evolution of temperature and water content within the ice.We find that a rapid transition between slow-moving ice outside the lake, and full sliding over the lake, can release considerable amounts of deformational energy, with the potential to form a temperate layer at depth in the transition zone. In addition, we provide an explanation for a characteristic surface feature commonly seen at the edges of subglacial lakes, a hummocky surface depression in the transition zone between little to full sliding. We also conclude that rapid changes in the horizontal extent of subglacial lakes and slippery patches, compared to the average ice column velocity, can create a traveling wave at depth within the isochrone structure that transfers downstream with the advection of ice, thus indicating the possibility of detecting past drainage events with ice penetrating radar.

Eurasian ice-sheet dynamics and sensitivity to subglacial hydrology

“…Ice generally moves more like an ice shelf over large lakes, with uniform velocity. Deformational and frictional heating thus largely disappear in the ice above them (Gudlaugsson and others, 2016). As the ice speeds up it gets drawn down by vertical flow at the edges and the ice surface tends to level above it.…”

Missing Evidence of Widespread Subglacial Lakes at Recovery Glacier, Antarctica

“…In this respect, Recovery Glacier is similar to the North East Greenland Ice Stream as shown in Vallelonga et al (2014). Layers within the ice are supposed to lower, once ice flows across a subglacial lake, as shown in Gudlaugsson et al (2016) and Leysinger Vieli et al (2007). There is no change in the layered structure upstream or across the large lakes (see Figure 11).…”

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 2: The role of grain size and premelting on ice deformation at high homologous temperature

“…The age of the ice is given in marine isotope stages (MIS) and approximate ka value (Lisiecki and Raymo, 2005 3405 unknown 3000 just below −10 * * not applicable MIS 3 (29-57 kyr) * Subglacial water encountered during drilling close to the bedrock. * * A specific temperature was not given, only that the grain size increase started just below −10 • C. 1 Gow and Williamson (1976), Hammer et al (1994), Gow and Engelhardt (2000), Epstein et al (2011). 2 EPICA community members (2004), Augustin et al (2007), Durand et al (2009).…”