The modelled liquid water balance of the Greenland Ice Sheet

Abstract

Abstract. Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS) contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB) of the ice sheet and its response to increasing surface melt. We therefore analyse a firn simulation conducted with the SNOWPACK model for the GrIS and over the period 1960–2014 with a special focus on the LWB and refreezing. Evaluations of the simulated refreezing climate with GRACE and firn temperature observations indicate a good model–observation agreement. Results of the LWB analysis reveal a spatially uniform increase in surface melt (0.16 m w.e. a−1) during 1990–2014. As a response, refreezing and run-off also indicate positive changes during this period (0.05 and 0.11 m w.e. a−1, respectively), where refreezing increases at only half the rate of run-off, implying that the majority of the additional liquid input runs off the ice sheet. This pattern of refreeze and run-off is spatially variable. For instance, in the south-eastern part of the GrIS, most of the additional liquid input is buffered in the firn layer due to relatively high snowfall rates. Modelled increase in refreezing leads to a decrease in firn air content and to a substantial increase in near-surface firn temperature. On the western side of the ice sheet, modelled firn temperature increases are highest in the lower accumulation zone and are primarily caused by the exceptional melt season of 2012. On the eastern side, simulated firn temperature increases are more gradual and are associated with the migration of firn aquifers to higher elevations.

A continuum model for meltwater flow through compacting snow

“…7. In agreement with Kuipers Munneke et al (2014) and Steger et al (2017a) we find that perennial firn aquifers occur when there Table 2. Typical numerical values for the surface energy balance (Cuffey and Paterson, 2010;van den Broeke et al, 2011).…”

Long‐Term Support of an Active Subglacial Hydrologic System in Southeast Greenland by Firn Aquifers

“…The position and drainage times of firn aquifers may allow disproportionately large influence on subglacial hydrology, even in near‐terminus regions, despite drainage volumes generally smaller than supraglacial lakes (Poinar et al, ). As the extent of Greenland firn‐aquifer water increases, drainage events may be more frequent, higher‐volume, or occur farther inland, further expanding the potential effect of firn‐aquifer drainage on ice flow (Miège et al, ; Steger, Reijmer, & van den Broeke, ).…”

“…Firn aquifers currently occupy areas low in the accumulation zone around much of the Greenland Ice Sheet (Miège et al, ), with inland expansion anticipated in future warm climates (Steger et al, ). If new surface‐to‐bed connections are made at inland locations, the subsequent evolution of the subglacial hydrologic system may alter ice dynamics (e.g., Bartholomew et al, ; Christoffersen et al, ; Clason et al, ; Doyle et al, ; Poinar et al, ).…”

Wet‐Snow Metamorphism Drives the Transition From Preferential to Matrix Flow in Snow

“…Water flow through snow dictates snowpack runoff generation (Hirashima et al, ; Wever et al, ), wet‐snow microstructure metamorphism (Avanzi et al, ; Brun, ), albedo evolution (Dietz et al, ), and settling (Marshall et al, ). Correctly simulating this process is thus a key toward better quantifying impacts of rain‐on‐snow events (Würzer et al, , ), wet‐snow avalanches (Baggi & Schweizer, ; Mitterer et al, ; Wever, Vera Valero, et al, ; Wever et al, ), and sea level rise (Forster et al, ; Harper et al, ; Machguth et al, ; Steger, Reijmer, van den Broeke, Wever, et al, ), all risks that are predicted to increase in a warming climate (e.g., Pielmeier et al, ; Steger, Reijmer, & Broeke, ).…”