Antarctica’s sleeping ice giant could wake soon

[Note:  This item comes from friend David Rosenthal.  DLH]

Antarctica’s sleeping ice giant could wake soon
The massive East Antarctic Ice Sheet looks stable from above — but it’s a dangerously different story below.
By Jane Qiu
Apr 12 2017
https://www.nature.com/news/antarctica-s-sleeping-ice-giant-could-wake-soon-1.21808

On a glorious January morning in 2015, the Australian icebreaker RSV Aurora Australis was losing a battle off the coast of East Antarctica. For days, the ship had been trying to push through heavy sea ice. It rammed into the pack, backed up and crashed forward again. But the ice, several metres thick, hardly budged. Stephen Rintoul, an oceanographer at the University of Tasmania in Hobart, Australia, nearly gave up his goal — to reach a part of the continent that had thwarted all previous expeditions. “I really thought that would be it,” he says. “It’d be another failed attempt.”

Then the weather came to the rescue, with a wind change that blew the ice away from the shore, opening a path through the pack. The ship managed to break free and wove its way through 100 kilometres of ice, reaching the edge of the frozen continent shortly after midnight. Rintoul and his team were the first scientists to reach the Totten Ice Shelf — a vast floating ice ledge that fronts the largest glacier in East Antarctica. “It was a really exhilarating experience,” says Rintoul, chief scientist of the expedition.

The team had to work fast before the ice closed again and blocked any escape. For more than 12 hours, Rintoul and his colleagues carried on non-stop, probing the temperature and salinity of the water, the speed and direction of ocean currents as well as the shape and depth of the ocean floor. They also deployed instruments that would continue taking measurements after the ship had departed.

These first direct observations confirmed a fear that researchers had long harboured: that warm waters from the surrounding ocean can sneak underneath the floating glacier tongue and eat the ice away from below1. “This could explain why Totten has been thinning in the past few decades,” says Rintoul.

Findings such as these are revealing some scary truths about East Antarctica — the vast, remote landmass to the east of the Transantarctic Mountains (see ‘Ice king’). This region is about as big as the entire United States and the majority of it stands on a high plateau up to 4,093 metres above sea level, where temperatures can plunge to −95 °C. Because the East Antarctic Ice Sheet seems so cold and isolated, researchers thought that it had been stable in the past and was unlikely to change in the future — a stark contrast to the much smaller West Antarctic Ice Sheet, which has raised alarms because many of its glaciers are rapidly retreating.

In the past few years, however, “almost everything we thought we knew about East Antarctica has turned out to be wrong”, says Tas van Ommen, a glaciologist at the Australian Antarctic Division in Kingston, near Hobart. By flying across the continent on planes with instruments that probe beneath the ice, his team found that a large fraction of East Antarctica is well below sea level, which makes it more vulnerable to the warming ocean than previously thought. The researchers also uncovered clues that the massive Totten glacier, which holds about as much ice as West Antarctica, has repeatedly shrunk and grown in the past2 — another sign that it could retreat in the future.

Although East Antarctica doesn’t seem to be losing much ice today, there are indications that it is feeling the heat of climate change and is responding in measurable ways. This is disconcerting because its ice sheet is more than ten times bigger than the one in the west. If all the ice below sea level in East Antarctica were to disappear, the height of the world’s oceans would swell by nearly 20 metres.

Researchers are now trying to gather as much information as possible about East Antarctica to better predict what’s to come. Their concern is that over the next few centuries, the ice sheet there might reach a tipping point. “Once glaciers retreat beyond a certain point, things may go downhill very quickly and cause rapid sea level rise,” says Eric Rignot, a glaciologist at the University of California, Irvine. “We don’t want to sleepwalk into a calamity like this.”

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