Liquid meltwater can sometimes flow deep below the Greenland Ice Sheet in winter, not just in the summer, according to work published on April 9 in the American Geophysical Union journal Geophysical Research Letters by Dr. Colin J. Gleason of the UMass Civil and Environmental Engineering (CEE) Department and his colleague Dr. Lincoln Pitcher at the University of Colorado Boulder.
As Gleason said about his CEE research lab, “We are a research group that cares about rivers, climate change, and the Artic. We do field work, we do remote sensing, and we model rivers in order to improve our basic understanding of these most important water features.”
According to the paper in Geophysical Research Letters, meltwater runoff from the Greenland Ice Sheet significantly contributes to sea level rise and is the dominant driver of enhanced mass loss in the sheet. While most melt occurs during summer, little is known about its seasonal and/or interannual retention within the Greenland Ice Sheet.
In February of 2015, Pitcher and Gleason deployed a ground-penetrating radar unit across frozen rivers downstream of the edge of the Greenland Ice Sheet and drilled boreholes to see if any water was leaving the ice sheet and flowing beneath river ice. They surveyed rivers draining five outlet glaciers of the Greenland Ice Sheet and discovered meltwater flowing at just one site, the Isortoq River.
“Here, we document evidence of runoff during winter, ~ four months after summer melt,” wrote Pitcher and Gleason. “Ground‐penetrating radar and borehole surveys in the proglacial Isortoq River reveal slowly flowing water beneath >0.5 meters of river ice. Geochemical analysis of this water indicates previous contact with the ice sheet bed.”
Pitcher and Gleason observed that comparable surveys in proglacial rivers draining four neighboring catchments found no winter drainage, despite a brief surface melt event more or less 10 days prior.
According to the two researchers, “We attribute the observed runoff to residual meltwater storage and release enabled by a >600-meters-deep trough beneath Isunguata Sermia, but not neighboring glaciers. We conclude that the Greenland Ice Sheet bed can stay wet and drain small amounts of meltwater year‐round.”
Gleason said that his CEE lab’s research focus is on basic science in several interrelated hydrologic disciplines as he seeks to develop new fundamental understanding of basic hydrologic processes and then apply them across the globe, particularly in the Artic.
Gleason engages in extensive Artic fieldwork in which he attempts to fill in hydrologic data gaps and provide validation for satellite-based products in this data-sparse but vulnerable region.
Gleason is also a member of the NASA Surface Water and Ocean Topography (SWOT) Science Team, for which he works with other SWOT members to guide NASA’s development of a novel satellite instrument by providing hydrologic rationale for measurement precision and accuracy considerations. In addition, Gleason is part of the calibration and validation efforts for this mission. (June 2020)