Brett Smith for redOrbit.com – Your Universe Online
Prevailing models from the melting of the Greenland ice sheet have made the calculation that the ice sheet sits atop hard bedrock.
A new study from a team of British and American scientists has thrown out that assumption, however, and found that the ice sheet may be melting faster than previously thought.
Published in the journal Nature Communications, the team’s report is based on the calculation, derived from ground surveys, that soft and porous sediments sit at the bed of the ice sheet.
The Greenland Ice Sheet spans about 660,000 square miles – around the size of Alaska. The massive sheet of ice, and others like it, is constantly in motion, and often this motion causes it to segment and break apart.
“When these large ice sheets melt, whether that’s due to seasonal change or a warming climate, they don’t melt like an ice cube,” said study author Marion Bougamont of Cambridge’s Scott Polar Research Institute. “Instead, there are two sources of net ice loss: melting on the surface and increased flow of the ice itself, and there is a connection between these two mechanisms which we don’t fully understand and isn’t taken into account by standard ice sheet models.”
Lakes which develop on the tops of glaciers, referred to as supraglacial lakes, often form in the summer. Researchers have discovered that many of these lakes drain in a matter of hours, when cracks open up and drain tremendous amounts of water into the subglacial space. In warmer years, these drainage events are predicted to become even more regular.
In the study, the researchers used a three-dimensional model, along with an observational data of surface area melting created by researchers at Aberystwyth University. The Cambridge scientists could then accurately recreate how the ice sheet’s periodic movements shifted in response to the quantity of surface meltwater being drained to the ground below.
“Not only is the ice sheet sensitive to a changing climate, but extreme meteorological events, such as heavy rainfall and heat waves, can also have a large effect on the rate of ice loss,” said study author Poul Christoffersen. “The soft sediment gets weaker as it tries to soak up more water, making it less resistant, so that the ice above moves faster. The Greenland Ice Sheet is not nearly as stable as we think.”
In this study, the scientists first used the overall quantity of surface runoff as a method for generating their model, but the end result from this experiment disagreed with observations. Next, the team looked at only water located briefly in supraglacial ponds on the ice sheet’s surface area. They discovered that only a small fraction of the meltwater which develops on the surface is held in supraglacial lakes and the high degree and rate of lake drainage events leads to the ice sheet accelerating, as has been previously witnessed.
The researchers concluded that there is a limit to how much water can be held in the ground underneath the Greenland Ice Sheet. This means the ice sheet is highly sensitive to global warming along with meteorological events, like heavy rainfall, which are projected to increase in frequency.
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