According to a new assessment from ESA’s CryoSat spacecraft, Antarctica is now losing 159 billion tonnes of ice a year to the ocean – twice as much as when the continent was last surveyed.
The CryoSat spacecraft has a radar instrument specifically designed to measure the shape of the ice sheet.
The melt loss from the White Continent is sufficient to push up global sea levels by around 0.43 mm per year.
Antarctica is now losing 159 billion tonnes of ice a year to the ocean
Scientists report the data in the journal Geophysical Research Letters.
The new study incorporates three years of measurements from 2010 to 2013, and updates a synthesis of observations made by other satellites over the period 2005 to 2010.
CryoSat has been using its altimeter to trace changes in the height of the ice sheet – as it gains mass through snowfall, and loses mass through melting.
The study authors divide the continent into three sectors – the West Antarctic, the East Antarctic, and the Antarctic Peninsula, which is the long finger of land reaching up to South America.
Overall, CryoSat finds all three regions to be losing ice, with the average elevation of the full ice sheet falling annually by almost 2cm.
In the three sectors, this equates to losses of 134 billion tonnes, 3 billion tonnes, and 23 billion tonnes of ice per year, respectively.
The East had been gaining ice in the previous study period, boosted by some exceptional snowfall, but it is now seen as broadly static in the new survey.
As expected, it is the western ice sheet that dominates the reductions.
Scientists have long considered it to be the most vulnerable to melting.
It has an area, called the Amundsen Sea Embayment, where six huge glaciers are currently undergoing a rapid retreat – all of them being eroded by the influx of warm ocean waters that scientists say are being drawn towards the continent by stronger winds whipped up by a changing climate.
About 90% of the mass loss from the West Antarctic Ice Sheet is going from just these few ice streams.
At one of them – Smith Glacier – CrysoSat sees the surface lowering by 9 m per year.
An American attempt to bore down into Lake Whillans, a body of water buried almost 1 kilometer under the Antarctic ice, has achieved its aim.
Scientists reported on Sunday that sensors on their drill system had noted a change in pressure, indicating contact had been made with the lake.
A camera was then sent down to verify the breakthrough.
The Whillans project is one of a number of such ventures trying to investigate Antarctica’s buried lakes.
In December, a British team abandoned its efforts to get into Lake Ellsworth after encountering technical difficulties.
The Russians have taken water samples from Lake Vostok, although they have yet to report any big discoveries.
Lake Whillans is sited in the west of Antarctica, on the southeastern edge of the Ross Sea.
It is less of a lake and more or a dense system of streams, almost like a delta, that covers some 60 square km. The liquid body is quite shallow – just a few metres in depth.
The Whillans Ice Stream Subglacial Access Research Drilling (Wissard) team has been using a hot-water drill to melt a 30-cm-diameter hole through the overlying ice.
An American attempt to bore down into Lake Whillans, a body of water buried almost 1 kilometer under the Antarctic ice, has achieved its aim
Breakthrough to the lake surface was reported on the project’s website.
The intention, now that the hole is secure, is to lower various sampling tools and sensors into the lake to study its properties and environment.
Some of the samples will be assessed onsite at the ice surface in temporary labs, and others will be returned to partner universities for more extensive analysis.
The Wissard blog said the thickness of the overlying ice was measured to be 801m, which agreed well with the estimates from seismic imaging.
More than 300 large bodies of water have now been identified under the White Continent.
They are kept liquid by geothermal heat and pressure, and are part of a vast and dynamic hydrological network at play under the ice sheet.
Some of the lakes are connected, and will exchange water. But some may be completely cut off, in which case their water could have been resident in one place for thousands of years, and that means they probably play host to microorganisms unknown to modern science.
The Whillans area is not as deep as either Vostok (4 km) or Ellsworth (3 km), and its water is exchanged frequently by the under-ice streams over months and years.
Indeed, satellite measurements have revealed the lake rapidly filling and draining. This was evident from measurements of the height of the overlying ice surface, which raised itself in response to an increase in water volume, and then slumped down as the water spread to a new location.
Scientists are keen to study Antarctica’s subglacial hydrological systems because liquid water beneath the ice sheet will influence its movement (the ice above Lake Whillans is moving at about 300m per year). Modeling the sheet’s long-term stability in a warming world has to take this into account.
These under-ice environments may also provide fascinating insights into the potential habitability of some moons in the Solar System.
Europa, a satellite of Jupiter, and Enceladus, which orbits Saturn, both have large volumes of liquid water buried beneath their icy crusts.