June 15th, 2013 by James Ayre
The Antarctic ice shelves have been melting at ever increasing rates in recent years — losing mass, though not always extent, as much of the mass loss has been with regards to ice thickness. And now, new research has shed some new light on the causes of this ice loss — the warming ocean waters have been melting the ice shelves from underneath, it’s not primarily the result of icebergs calving into the ocean as was previously thought.
The new research — representing the first comprehensive survey of all Antarctic ice shelves — has found that basal melt (ice dissolving from underneath) was responsible for 55% of all ice shelf loss from 2003 to 2008. That is a much higher rate than was previously assumed. As a reminder of why this matters — ice shelves, which are essentially the floating extensions of glaciers, surround 75% of the absolutely enormous frozen continent.
The researchers think that this new work will allow others in the field to “improve projections of how Antarctica, which holds about 60% of the planet’s fresh water locked in its massive ice sheet, will respond to a warming ocean and contribute to sea level rise.” How the ice sheets of Antarctica will respond to the significant warming that is predicted to occur over the next 100 years is an important question — one which is especially important when you consider that the vast majority of the world’s most important economic regions are relatively close to coastlines. Rising seas as well as increasing flood/storm events could have devastating consequences for many of the world’s largest economies.
Back to the research — as the researchers put it “it turns out that the tug of seawaters just above the freezing point matters more than the breaking off of bergs.”
“We find that iceberg calving is not the dominant process of ice removal. In fact, ice shelves mostly melt from the bottom before they even form icebergs,” explained lead author Eric Rignot, a UC Irvine professor, and also a researcher at NASA’s Jet Propulsion Laboratory. “This has profound implications for our understanding of interactions between Antarctica and climate change. It basically puts the Southern Ocean up front as the most significant control on the evolution of the polar ice sheet.”
The press release provides context and details:
Ice shelves grow through a combination of land ice flowing to the sea and snow falling on their surfaces. The researchers combined a regional snow accumulation model and a new map of Antarctica’s bedrock with ice shelf thickness, elevation and velocity data captured by Operation IceBridge — an ongoing NASA aerial survey of Greenland and the South Pole.
Ocean melting is distributed unevenly around the continent. The three giant ice shelves of Ross, Filchner and Ronne, which make up two-thirds of Antarctica’s ice shelves, accounted for only 15 percent of the melting. Meanwhile, less than a dozen small ice shelves floating on relatively warm waters produced half the total meltwater during the same period.
The researchers also compared the rates at which the ice shelves are shedding ice with the speed at which the continent itself is losing mass and found that, on average, the shelves lost mass twice as fast as the Antarctic ice sheet did.
“Ice shelf melt can be compensated by ice flow from the continent,” Rignot said. “But in a number of places around Antarctica, they are melting too fast, and as a consequence, glaciers and the entire continent are changing.”
While rising sea levels are themselves an issue, the real issue — and one that is not often mentioned — is that as sea levels rise, more and more economically and industrially important infrastructure will be exposed to storm and flood events. Events similar to Hurricane Sandy, to Hurricane Katrina, could become very common — that would have a devastating effect on the economies of the affected regions. Something to keep in mind…
The new research was just published in the June 14 issue of Science.
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