Snekerne

A firn core collected on the Greenland ice sheet showing refrozen meltwater (darker section in the middle) saturates the porous firn (brighter section on the sides).

Baptiste Robert Marcel Vandecrux

Postdoc
Glaciology and Climate
27-03-2019
News

The meltwater retention capacity of the snow blanket covering the Greenland ice sheet is decreasing

A new study of the thick snow blanket, also called firn, covering the Greenland ice sheet finds that due to a decrease in the firn porosity in western Greenland, less of the meltwater generated in these regions will be retained in the firn and more will end up in the sea.

Researchers have investigated the Greenland ice sheet since the 1950s for various purposes – e.g. military infrastructure, meteorology, satellite data interpretation, etc. These research teams have collected precious information about the characteristics of the snow covering the Greenland ice sheet, but the data remained unused after the completion of each of these projects.

Recently, increasing attention was brought to the thick, multi-year snow blanket, also called firn, that covers the Greenland ice sheet, because of its capacity to buffer the ice sheet’s contribution to sea-level rise. In a recent study, Baptiste Vandecrux, ph.d. student at the Geological Survey of Denmark and Greenland (GEUS) and at The Technical University of Denmark (DTU) compiled historical and contemporary measurements of the Greenlandic firn to give an unprecedented view of the state of the firn on the largest ice sheet in the Northern hemisphere.

Like a sponge, the firn can retain meltwater within its pores

Using 360 observations spanning from 1953 to 2017, Baptiste Vandecrux and a group of scientists from Denmark, USA, Switzerland, Germany and England, were able to describe the porosity, or air content, of the firn across the Greenland ice sheet. The firn porosity is of great interest because it controls the capacity of the firn to retain the increasing surface melt that comes with climate warming in Greenland. Firn air content is also useful for the interpretation of satellite observations from the ice sheet.

“The study shows that the firn in the lower end of the western slope of the ice sheet contained 23 % less air in recent measurements compared to surveys in the 90s and early 2000s. This decrease of porosity originates from the recent increase of surface melt and meltwater refreezing within the firn and indicates that the firn can host 23 % less meltwater within its pores,” Baptiste Vandecrux explains. He continues:

“It also means that potentially more of the melt generated in these regions will end up in the sea and contribute to sea level rise instead of being retained within the porous firn.”

The new open-access study was published in The Cryosphere.

Map

a) Maps of the firn air content on the Greenland ice sheet derived from historical and temporary observation. b) Spatial pattern of the firn air content decrease in Western Greenland. Credit: Baptiste Vandecrux et al. https://doi.org/10.5194/tc-13-845-2019