August 13, 2013
Effect Of Glacial Melt On Sea Level Less Dramatic Than Believed
Brett Smith for redOrbit.com - Your Universe Online
Occasionally, melt water on top of a glacier will trickle down to the bedrock below and act as a lubricant for the glacier’s movements. Once thought to be a major contributor to sea-level rise, melt water was found to have only a minor effect on sea level in a new study from a team of European and American scientists.
Using computer modeling based on observations of Greenland’s ice sheet, the research team concluded glacier lubrication would add less than one-third of an inch to sea-level rise by 2200, according to their report in the Proceedings of the National Academy of Sciences.
“This is an important step forward in our understanding of the factors that control sea-level rise from the Greenland Ice Sheet,” said lead author Sarah Shannon, a PhD researcher from the University of Bristol. “Our results show that melt-water enhanced lubrication will have a minor contribution to future sea-level rise. Future mass loss will be governed by changes in surface melt-water runoff or iceberg calving."
Scientists had thought melt-water created cavities at the bottom of the glacier that had a lifting effect – speeding up the ice masses’ progress. Previous theories have gone on to say that more melt-water would lead to additional lubrication and an acceleration of the ice flow.
However, this latest study has shown greater amounts of melt-water can create channels under the ice that act as drains and actually reduces the water's lubricating effect. The research team also discovered that the effect of melt-water on sea levels is relatively small, regardless of its influence on glacier lubrication.
"We found that the melt-water would lead to a redistribution of the ice, but not necessarily to an increase in flow,” Shannon said.
The new study is one result of the European-funded ice2sea program. The collaboration among 24 institutions across Europe previously produced research showing shifts in surface melting of the ice sheet will be the primary factor in determining how Greenland contributes to sea-level rise.
“This is important work but it's no reason for complacency,” said David Vaughan, an ice2sea coordinator based at the British Antarctic Survey in Cambridge. “While this work shows that the process of lubrication of ice flow by surface melting is rather insignificant, our projections are still that Greenland will be a major source of future sea-level rise.”
“As we have reported earlier this year, run-off of surface melt water directly into the ocean and increased iceberg calving are likely to dominate,” he added.
While some researchers focus on the melting occurring on top of Greenland’s massive ice sheet, others are concerned with forces acting from below. A study published this week in Nature Geoscience found the heat from the Earth's mantle is significantly affecting the rate of glacial melt in Greenland.
“The temperature at the base of the ice, and therefore the current dynamics of the Greenland ice sheet is the result of the interaction between the heat flow from the Earth’s interior and the temperature changes associated with glacial cycles,” explained study researcher Irina Rogozhina from Germany’s GFZ German Research Centre for Geosciences. “We found areas where the ice melts at the base next to other areas where the base is extremely cold.”