Initialization of an ice-sheet model for present-day Greenland

Abstract

AbstractWe construct initial conditions for an ice flow model of the Greenland ice sheet (GrIS). GrIS has been losing mass at an increasing rate over the past two decades, and a significant proportion of this loss is due to dynamic thinning of narrow outlet glaciers. We solve an inverse problem to estimate poorly known basal and englacial parameters given observed geometry and surface velocities. A weighted cost function, resolved to 4 km in the interior of the ice sheet and 1 km in regions of fast-flowing ice at the margin, is minimized to find two-dimensional fields for a stiffness factor, which is a coefficient of the effective viscosity, and basal traction coefficient. Using these fields, we run the model under present-day climate to damp large-amplitude, short-wavelength fluctuations in the flux divergence. The time-dependent model uses an adaptive mesh with resolution ranging from 8 km of the base grid to 500 m in areas of fast-flowing ice to capture the behaviour of the main outlet glaciers. The ice discharge calculated from the initial conditions for GrIS and individual glaciers compares well with values calculated from observations.