Recent projections have identified East Antarctica’s fast-flowing Recovery Glacier, which drains 10% of the continent’s land-based ice, as the region’s largest potential contributor to future global sea level rise. Scientists have hypothesized that water derived from four previously identified subglacial lakes, which are located near the point where Recovery Glacier’s flow accelerates, largely controls the glacier’s discharge.
To better understand the distribution and role of subglacial water within the Recovery system, Diez et al. analyzed two sets of airborne radar data acquired through the IceGrav project in 2013 and the PolarGap project in December of 2015. The combined data set comprises a grid with an overall line spacing of about 10 kilometers across Recovery Lakes A, B, and C, plus a single line across Lake D.
Using several properties, including ice thickness, bed roughness, and radar reflectivity, the researchers classified whether the subice terrain in each grid cell is a lake, a swamp, or dry. Their results suggest that the areas previously classified as Lakes C and D are actually dry and the area comprising the originally proposed Lakes A and B is instead an interconnected, 4,320-square-kilometer swampland, consisting of small lakes surrounded by saturated sediment, which the team renamed Lake AB. These findings are consistent with another recently published article that found no definitive evidence of lakes in these locations.
Using updated charts of bed topography and calculated flow paths, the team also mapped where water is discharging from the lakes. These data indicate that subglacial water seeps from Lake AB’s western shore, lubricating the bed and initiating the rapid ice flow observed in this area.
By contrast, the authors attribute the onset of fast ice flow observed near what was previously interpreted as Lakes C and D to the presence of a substantial topographic step. The resulting 1,300-meter increase in ice thickness—rather than lubrication of the bed—suffices to explain the onset of fast ice flow in this area.
These findings indicate that multiple processes are responsible for speeding up the flow of ice within the Recovery Glacier system. Because not all of these relate to subglacial water, this study demonstrates the importance of characterizing the underlying causes of ice flow acceleration to gain a more nuanced understanding of how this water could affect the glacier’s discharge in a range of future climate change scenarios. (Journal of Geophysical Research: Earth Surface, https://doi.org/10.1029/2018JF004799, 2019)
—Terri Cook, Freelance Writer