This study is part of Operation IceBridge, a multi-year NASA mission, is the largest airborne survey of Earth's polar ice ever flown. It yields an unprecedented three-dimensional view of Arctic and Antarctic ice sheets, ice shelves and sea ice. These flights provide a yearly, multi-instrument look at the behavior of the rapidly changing features of the Greenland and Antarctic ice.

Meltwater beneath the large ice sheets can influence ice flow by lubrication at the base or by softening when meltwater refreezes to form relatively warm ice. Refreezing has produced large basal ice units in East Antarctica. Bubble-free basal ice units also outcrop at the edge of the Greenland ice sheet, but the extent of refreezing and its influence on Greenland’s ice flow dynamics are unknown. Here we demonstrate that refreezing of meltwater produces distinct basal ice units throughout northern Greenland with thicknesses of up to 1,100 m. We compare airborne gravity data with modelled gravity anomalies to show that these basal units are ice. Using radar data we determine the extent of the units, which significantly disrupt the overlying ice sheet stratigraphy. The units consist of refrozen basal water commonly surrounded by heavily deformed meteoric ice derived from snowfall. We map these units along the ice sheet margins where surface melt is the largest source of water, as well as in the interior where basal melting is the only source of water. Beneath Petermann Glacier, basal units coincide with the onset of fast flow and channels in the floating ice tongue. We suggest that refreezing of meltwater and the resulting deformation of the surrounding basal ice warms the Greenland ice sheet, modifying the temperature structure of the ice column and influencing ice flow and grounding line melting.

Funding: NASA grants NNX10AT69G and NNG10HP20C

Duration (of participation): November 2011 - October 2012

Project Output:

  • Presented as a poster (#C41E-0450) at the American Geophysical Union Annual Meeting (2011)

  • Published as a research article in Nature Geoscience.