Twenty-five years of satellite observations have been used to reconstruct a detailed history of Antarctic ice shelves.
These ice platforms are floating extensions of glaciers that flow from the ground and ring across the continent.
The European Space Agency data set confirms the trend of melting shelves.
In all, they have spilled close to 4,000 gigatonnes since 1994 – a melt that could fill America’s Grand Canyon.
But the innovation here is not so much the fact that the shelves are losing mass – we already knew it; the relatively warm ocean water is eating their sides. Rather, it is the finished statements that can now be made about exactly where and when the waste occurred, and where the melt water is also going.
Some of this cold and fresh water has entered the deep sea around Antarctica, where it is undoubtedly affecting ocean circulation. And that could have consequences for the climate far beyond the South Pole.
“For example, there have been some studies that have shown that including the effect of melting Antarctic ice on models slows down global ocean temperature rise, and that could actually lead to an increase in rainfall in the US,” he explained. Susheel Adusumilli from the Scripps Institute of Oceanography in San Diego.
Mr. Adusumilli and colleagues analyzed all observations made from the long series of Esa radar missions – ERS-1, ERS-2, EnviSat and CryoSat-2.
These spacecraft have been tracking the change in thickness on Antarctic ice shelves since the early 1990s.
Combining their data with ice velocity information from other sources, and the results of computer models – the Scriptps group has acquired a high-resolution view of the melting model during the study period.
As might be expected, there have been many changes, with mass losses and gains, even within the same individual shelf. And the rate of massive loss over time has also gone up and down. But the overall picture is clear: the shelves are running out.
“We see that the merger is always above the steady state values,” said Mr. Adusumilli for BBC News. “You only need a certain amount of melting to keep the ice sheet in balance. But what we have seen is an amount of melting from the ocean that is more than enough to keep it in balance.”
The interesting aspect of this study is that scientists can now trace exactly where in-depth melting is taking place. Some of these floating ice platforms (the largest is the size of France) lie many hundreds of meters below sea level.
Researchers can tell from satellite data whether debris is occurring near the thinnest parts of shelves or on their fronts, or deep in those places where glacier ice coming out of the ground first becomes hard and starts to float.
“That kind of information can tell us a lot about the melting processes involved, how they are working – and the effects that melting melting can have,” said Script Professor ‘Helen Fricker.
“So it’s not just that the shelves are melting. How they are melting – and where their melted water is being injected into the ocean.”
Thinning of ice shelves does not directly contribute to sea level rise. This is because floating ice has already shifted its equivalent volume of water.
But there is an indirect consequence. If the shelves weaken, the ice of the land behind may flow faster into the ocean, and this will lead to sea level rise. This is happening, and has been measured by other satellites.
Prof. David Vaughan is the director of science at the British Antarctic Survey. It was not related to the study which was published in Nature Geoscience.
He told BBC News: “The Scriptps team has produced a map of Antarctica that shows it sparse around the margin on a shredded red and blue belt. The details on the coastline are absolutely phenomenal.
“We can really identify the parts of the ice shelves that are most essential to the history of thinning. There will be a lot of ecologists who spend a lot of time looking at where thawing and thinning is really happening. Exactly why those areas have been affected.”
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