Articles | Volume 8, issue 6
Model description paper
02 Jun 2015
Model description paper |  | 02 Jun 2015

Mass-conserving subglacial hydrology in the Parallel Ice Sheet Model version 0.6

E. Bueler and W. van Pelt

Abstract. We describe and test a two-horizontal-dimension subglacial hydrology model which combines till with a distributed system of water-filled, linked cavities which open through sliding and close through ice creep. The addition of this sub-model to the Parallel Ice Sheet Model (PISM) accomplishes three specific goals: (a) conservation of the mass of water, (b) simulation of spatially and temporally variable basal shear stress from physical mechanisms based on a minimal number of free parameters, and (c) convergence under grid refinement. The model is a common generalization of four others: (i) the undrained plastic bed model of Tulaczyk et al. (2000b), (ii) a standard "routing" model used for identifying locations of subglacial lakes, (iii) the lumped englacial–subglacial model of Bartholomaus et al. (2011), and (iv) the elliptic-pressure-equation model of Schoof et al. (2012). We preserve physical bounds on the pressure. In steady state a functional relationship between water amount and pressure emerges. We construct an exact solution of the coupled, steady equations and use it for verification of our explicit time stepping, parallel numerical implementation. We demonstrate the model at scale by 5 year simulations of the entire Greenland ice sheet at 2 km horizontal resolution, with one million nodes in the hydrology grid.

Short summary
We describe and test a parallel 2-D subglacial hydrology model. Such a hydrology model describes the motion of liquid water, and its pressure, underneath ice sheets and glaciers. Model goals include conserving the mass of water and generating an estimate of the ice basal shear stress. This hydrology model describes the subglacier as a layer of till and linked cavities, but it does not include conduits.