Denman Glacier marks the deepest point on continental Earth, reaching about 11,480ft (3,500m) below sea-level. The glacier is located in East Antarctica where it holds about as much as ice as half of West Antarctica. NASA scientists have now discovered the glacier is retreating both above and below the waterline.
The discovery, which paints a worrying picture for global sea-level rise, was published in the journal Geophysical Research Letters.
Between 1996 and 2018, the so-called grounding line along the glacier’s western flank has retreated by about 3.4 miles (5.4km).
The grounding line marks the point where the glacial ice is attached to the bedrock.
Beyond the grounding line, the ice floats on the ocean in the form of a shelf or sheet of ice known as an ice tongue.
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As a result of the glacial retreat, more of the glacial’s underside comes in contact with water that could potentially warm it and melt it.
If the grounding continues, the warmer seawaters threaten to travel farther under the glacier.
Virginia Brancato, the study’s lead author and scientist at NASA’s Jet Propulsion Laboratory (JPL), said: “Because of the shape of the ground beneath Denman’s western side, there is potential for the intrusion of warm water, which would cause rapid and irreversible retreat and contribute to global sea-level rise.”
Along its eastern flank, Denman Glacier runs a six-mile-wide (10km) underwater ridge.
We are beginning to see evidence of potential marine ice sheet instability in this region
Eric Rignot, NASA JPL
On the western flank, however, the glacier sits on a 5,900ft (1,800m) trough that extends inland.
If the glacier’s retreat continues, the trough could funnel warmer seawaters deep into the Antarctic.
With global warming already affecting temperatures and sea currents, there is an additional concern for the stability of the region.
Eric Rignot, a cryospheric scientist at JPL and study co-author, said: “East Antarctica has long been thought to be less threatened, but as glaciers such as Denman have come under closer scrutiny, we are beginning to see evidence of potential marine ice sheet instability in this region.
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“The ice in West Antarctica has been melting faster in recent years, but the sheer size of Denman Glacier means that its potential impact on long-term sea-level rise is just as significant.”
Satellite images obtained by NASA’s Landsat 8 satellite show how far the grounding line has retreated in just 22 years.
The pink line in the above image shows the grounding line’s border in 1996.
The 2018 measurements are marked in yellow and ice in the image flows from the left to the right.
In another map, the scientists have measured the velocity of ice flows escaping the glacier.
In this image, grounded ice from the Denman Glacier can be seen flowing to the left, to the Denman Ice Tongue.
About 9,000 square miles (24,000 square km) of Denman are afloat.
Scientists estimate the floating ice has been melting at a rate of about 10ft (3m) annually.
The measurements were obtained by NASA’s Operation IceBridge as well as the German Aerospace Center’s TanDEM-X satellite and the Italian COSMO-SkyMed satellites.
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