PARIS – Accelerating ice loss from the Antarctic ice sheet could be due in part to active volcanoes under the frozen continent’s eastern part, a study said Sunday.
From 2002 to 2011, the average annual rate of Antarctic ice sheet loss increased from about 30 billion tons to about 147 billion tons, the U.N.’s panel of climate scientists reported in September.
Ice sheets are masses of glacial land ice. One such sheet covers most of Greenland and another Antarctica, and together they contain most of the freshwater on Earth.
The sheets are constantly moving, slowly flowing downhill and seaward under their own weight. Portions that extend out over the ocean are called ice shelves.
Previous research has blamed warmer seas swirling in a circular fashion around Antarctica for the quicker pace of ice-sheet loss from the southernmost continent.
These waters erode ice shelves, went the theory. And as more of the shelves disappeared, the sheet would flow faster and lose more ice to the sea.
But in a new paper in the journal Nature Geoscience, geologists led by Amanda Lough at Washington University in St. Louis, Missouri, suggested that, in west Antarctica, the faster flow may be also be due to volcanoes.
These heat the underside of the ice, causing melting that lubricates the flow, they suggested.
Evidence for this comes from recently deployed sensors that recorded two “swarms” of seismic activity under Mary Byrd Land, a highland region of west Antarctica, in 2010 and 2011.
Using ice-penetrating radar, the team found an intriguing elliptical deposit, measuring about 1,000 sq. km in the area, at a depth of 1,400 meters.
The deposit is believed to be volcanic ash, spewed out by an enormous eruption some 8,000 years ago. The age estimate was reached using the assumption that the ash has been covered over time by ice accumulating at the rate of 5 inches (12.5 cm) per year.
“Together, these observations provide strong evidence for ongoing magmatic activity and demonstrate that volcanism continues to migrate southward.”
Several volcanoes were known to exist in west Antarctica, but none were thought to be active.
“Eruptions at this site are unlikely to penetrate the 1.2- to 2-km-thick overlying ice, but would generate large volumes of melt water that could significantly affect ice stream flow,” said the study.