Sunday, 18 December 2016

Antarctica is melting

East Antarctica is Melting From Above and Below



18 December, 2016


East Antarctica is remote even by Antarctic standards. Harsh winds and ocean currents have largely cut off the region from the rest of the world.

That’s left its massive stores of ice largely intact, especially compared to West Antarctica where a massive meltdown is underway that could raise seas by 10 or more feet in the coming centuries. But as carbon pollution warms the air andthe ocean, there are signs that the region’s stability is under threat. Two new studies of different ice shelves — tongues of ice that essentially act as bathtub plugs — have seen major melting that could portend a less stable future for the region.

The calving front of the Totten ice shelf.
Credit: Australian Antarctic Division

So first, about those ice shelves. They are indeed like bathtub plugs. Except instead of keeping water in a tub, they keep ice on the continent of Antarctica. That’s good because when it ends up melting into the ocean, it causes seas to rise. East Antarctica contains about two-thirds of all the ice in Antarctica so its stability is crucial for the world’s coastal areas.


But strange things have been happening recently. During a 2014 flyover of the Roi Baudouin ice shelf, scientists noticed a curious depression more than a mile wide in the undulating ice. When they finally investigated it in January this year, they found walls that were about 10 feet high and meltwater pouring into moulins — features that funnel surface meltwater into the heart of the ice.

The moulins were just one sign of melt happening on the surface. When scientists drilled a hole in the ice and lowered a camera, they found an otherworldly blue lake stretching more than half a mile across.

Research published in Nature Climate Change shows that the cause of these bizarre features are the powerful winds that blow down from Antarctica’s interior. Jan Lenaerts, a postdoctoral researcher at the Utrecht University in the Netherland who led the study, said that those winds helped heat the air and caused white ice to melt out, exposing a layer of dark ice beneath. That darker ice in turns absorbs more sunlight, further expediting the melt.

Although we only found this on one ice shelf, we find the same mechanisms on many East Antarctic ice shelves,” Lenaerts said. “Given the strong response of surface meltwater production and extent of meltwater processes on the shelf to summer temperature, we can expect that in a warmer climate, these ice shelves might be vulnerable to instability that is driven by meltwater hydrofracturing.”
This on its own would be distressing news for the planet’s coastal communities

But there are also signs that warm water is undercutting at least one of East Antarctica’s other ice shelves. The Totten ice shelf is one of the most important ice shelves in the region. It backstops so much ice that if it were to melt, it would result in up to 12 feet of sea level rise.

Recent research has shown that its geology and interactions with the ocean mean that losing just 4.2 percent of its mass could kickstart the process to send more inland ice to the sea. And it has been melting faster than most other glaciers and ice shelves in East Antarctica.

We knew from satellite data that the Totten has been thinning faster than other glaciers in East Antarctica, but we didn’t know why,” Steve Rintoul, the interim head of CSIRO’s Climate Science Center, said in a statement.

That’s why Rintoul and his colleagues set out to look more closely at the ice in January 2015 on the Aurora Australis, an Australian research boat. They were able to visit the calving front of the ice — where the shelf ends in the ocean — thanks to a fortuitous path that broke in the sea ice in January 2015. It’s the first time direct measurements have ever been taken by boat in the region.

Their findings from that trip, published on Friday in Science Advances, show that the bedrock underlying the ice shelf is a major driver in the melt process. They found two massive ocean channels up to 6 miles wide and a half mile deep are funneling warm water under the ice shelf and melting it out from underneath.

Taken individually, the studies are disconcerting enough. Put together, though, they paint a picture of a region that could become a much bigger player in sea level rise if carbon pollution isn’t curtailed soon.


This Melting Glacier in Antarctica Could Raise Sea Levels By 11 Feet



18 December, 2016

The Earth’s climate, it seems, isn’t listening to the politicians that are insisting it’s not warming. The temperature continues to rise incrementally, and the globe’s large glaciers—giant vaults of stored water—continue to melt, releasing into the oceans. The global sea level, due to thermal expansion and glacial melting, continues to rise, building up a head of steam like a train just beginning its descent down a steep hill.

Greenland’s hulking glacier and the Arctic Sea ice are now marked by their rapid melting. And the western Antarctic ice sheet has garnered a lot of attention recently, too. But while scientists were fretting over the western side of Antarctica, the eastern Antarctic ice sheet has been melting too. Australian researchers braved treacherous sea conditions to collect data on the melting Totten Ice Shelf there, which holds up a body of ice that would cause over 11 feet of sea level rise, if it melted. Their findings are published in the journal Science Advances.

Scientists have concluded that ice shelves and glaciers in eastern Antarctica have been experiencing basal melt, where the bottom layer of a body of ice starts to melt away, but they’ve never directly observed how it’s happening and what the main drivers of melting are until now.
The Totten Ice Shelf. Image: Esmee van Wijk (CSIRO and ACE CRC)

In Antarctica, the ice sheets covering the continent are so large that they extend beyond the land’s edge. Picture a pool cover that’s only covering half of an in-ground pool. Part of it lays on the patio nearby, and the rest of it slopes downward onto the water’s surface where it floats. Where the glacier hits the water is a buttress of ice called a shelf, which keeps the land bound ice from draining into the sea. If the shelf melts then—well, you get the idea. Such is the Totten Ice Shelf.
Recovery of a mooring in heavy sea ice near the Totten Ice Shelf. Image: Steve Rintoul (CSIRO and ACE CRC)

With fair weather conducive to research, oceanographer and lead author of the study,Stephen Rich Rintoul, of the Commonwealth Scientific and Industrial Research Organization in Australia, directed a team of scientists to collect oceanographic data from the Totten ice front in east Antarctica. Previous expeditions were hampered by heavy sea ice conditions and ultimately unsuccessful. What they found was startling.

The RSV Aurora Australis at the front of the Totten Glacier. Image: Paul Brown (Australian Maritime College)

About 2,000 feet down, the team found a great trough—about 6 miles wide—worn into the side of the Totten shelf. Below 2,000 feet the gaping cavity narrows into two channels, and warm water flows through it, boring through the ice like sugar through the enamel of a tooth. The ice shelf, they measured, is melting at its base faster than all other ice shelves of similar size in East Antarctica. If it were to give way, enough ice would slide into the sea to raise global levels by over 11 feet.
Successful recovery of an oceanographic mooring near the Totten Ice Shelf. Image: Steve Rintoul (CSIRO and ACE CRC)

How the melting of these great bodies of ice will play out in the future remains to be seen, but regardless of any continuing work done to slow the effects of climate change, it’s possible the damage is already done. Giants slabs of ice that give way 10 years from now, for example, could be the product of melting that started a decade ago. Climate scientist Kerim Nisancioglu, of the University of Bergen, told the New Yorker that

In some cases, you have, in theory, this irreversible process. You set it off and it just goes. It drains.” It’s a wait and see.


1 comment:

  1. The SHTF climate wise and it's only going to hit the fan more. :-(

    ReplyDelete