Modeling the response of subglacial drainage at Paakitsoq, west Greenland, to 21^stcentury climate change

Abstract

Although the Greenland Ice Sheet (GrIS) is losing mass at an accelerating rate, much uncertainty remains about how surface runoff interacts with the subglacial drainage system and affects water pressures and ice velocities, both currently, and into the future. Here, we apply a physically based, subglacial hydrological model to the Paakitsoq region, west Greenland, and run it into the future to calculate patterns of daily subglacial water pressure fluctuations in response to climatic warming. The model is driven with moulin input hydrographs calculated by a surface routing model, forced with distributed runoff. Surface runoff and routing are simulated for a baseline year (2000), before the model is forced with future climate scenarios for the years 2025, 2050, and 2095, based on the IPCC's Representative Concentration Pathways (RCPs). Our results show that as runoff increases throughout the 21 st century, and/or as RCP scenarios become more extreme, the subglacial drainage system makes an earlier transition from a less efficient network operating at high water pressures, to a more efficient network with lower pressures. This will likely cause an overall decrease in ice velocities for marginal areas of the GrIS. However, short-term variations in runoff, and therefore subglacial pressure, can still cause localized speedups, even after the system has become more efficient. If these short-term pressure fluctuations become more pronounced as future runoff increases, the associated late-season speedups may help to compensate for the drop in overall summer velocities, associated with earlier transitioning from a high to a low pressure system.

The past, present, and future viscous heat dissipation available for Greenland subglacial conduit formation

“…However, this approach limits the focus of these studies to recent seasons for which abundant in situ sensor data exist. In order to examine future scenarios, Mayaud et al (2014) built on the work of Banwell et al (2013) but used a conduit model that includes melt opening and creep closure, driven by a positive degree day runoff model, to examine future changes to year 2095 under various IPCC RCP scenarios (Moss et al, 2010). Those models had hourly or daily resolution and were again limited to the southwest sector of the ice sheet.…”

“…In the southwest sector, Mayaud et al (2014) have bridged the gap spatially between the margin and the interior, and temporally between present and future, using the same runoff and RCP scenarios used in this study. They show that near the margin in the Paakitsoq region, conduits are likely to form earlier, remain longer, and reduce glacier velocity under RCP4.5 and 8.5 compared to present.…”

“…Numerical models and observations of the Greenland Ice Sheet (GIS) link surface meltwater penetration to the bed to both short (hourly, daily) and long (seasonal, decadal) temporal variations in ice velocity (Zwally et al, 2002;Bartholomew et al, 2011;Banwell et al, 2013;Shannon et al, 2013;Mayaud et al, 2014;Tedstone et al, 2015). However, the link between increased basal water inputs and ice sliding is a complex one, largely because viscous heat dissipation (VHD) from water flow beneath ice may melt out efficient drainage tunnels whose presence may decrease, or even reverse, the tendency for ice flow to accelerate with increasing meltwater inputs to the bed (Kamb, 1987;Sundal et al, 2011;Tedstone et al, 2015).…”

Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change

“…Some studies suggested that this occurs through the subglacial drainage system becoming more efficient with increased discharge, thus reducing basal sliding [99,100]. Mayaud et al [101] forced a subglacial hydrological model of the western ice sheet margin in the Paakitsoq region with surface runoff that was derived from climate model output for the RCP2.6, 4.5, and 8.5 scenarios. They showed that as runoff increases in response to a warmer climate, the subglacial drainage system transitions from a less efficient network with associated higher basal sliding to a more efficient network with an associated reduction in basal sliding.…”

Toward Monitoring Surface and Subsurface Lakes on the Greenland Ice Sheet Using Sentinel-1 SAR and Landsat-8 OLI Imagery

“…Lake drainage events are important in opening up moulins, which act as connections between the surface and bed, allowing continued delivery of water through the summer to the subglacial drainage system, facilitating its seasonal evolution and impacting basal water pressures and ice motion over the longer term (Bartholomew et al, 2010;Sole et al, 2013;Tedstone et al, 2013). Increasing amounts of meltwater at higher elevations in the future may allow more lakes to form and drain in those locations, which may lead to an increased hydraulic efficiency of the subglacial drainage system through the formation of channels; however, this is unknown (Mayaud et al, 2014;Leeson et al, 2015).…”