A modeling study of the effect of runoff variability on the effective pressure beneath Russell Glacier, West Greenland

Basal sliding is a main control on glacier flow primarily driven by water pressure at the glacier
base. The ongoing increase in surface melting of the Greenland Ice Sheet warrants an examination of its
impact on basal water pressure and in turn on basal sliding. Here we examine the case of Russell Glacier,
in West Greenland, where an extensive set of observations has been collected. These observations suggest
that the recent increase in melt has had an equivocal impact on the annual velocity, with stable flow on
the lower part of the drainage basin but accelerated flow above the Equilibrium Line Altitude (ELA). These
distinct behaviors have been attributed to different evolutions of the subglacial draining system during and
after the melt season. Here we use a high-resolution subglacial hydrological model forced by reconstructed
surface runoff for the period 2008 to 2012 to investigate the cause of these distinct behaviors. We find that
the increase in meltwater production at low elevation yields a more efficient drainage system compatible
with the observed stagnation of the mean annual flow below the ELA. At higher elevation, the model
indicates that the drainage system is mostly inefficient and is therefore strongly sensitive to an increase in
meltwater availability, which is consistent with the observed increase in ice velocity.