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Jesse Allen/NASA Earth Observatory

Antarctica Is Covered in Rivers, Lakes, and Waterfalls. That Might Not Be Good.

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Jesse Allen/NASA Earth Observatory

The floating ice shelves that buttress Antarctica are less icy than we thought, it turns out. They’re filled with flowing water. New research published in the scientific journal Nature maps the extensive network of meltwater from Antarctica's ice sheets and found that, contrary to previous understanding, lakes and rivers—even waterfalls—created by melting have been common for at least seven decades.

Two new papers analyze satellite imagery of Antarctica dating back to 1973 and aerial photography dating back to 1947 for evidence of meltwater. Warming oceans melt ice shelves around from the bottom up, while warming air temperatures melt them from the top down, creating pools and rivers of liquid water on the continent's surface.

Researchers found that over the last 70 years, a system of meltwater drainage has transported water from the continent of Antarctica across the floating ice shelves that surround it, traveling up to 75 miles and creating ponds up to 50 miles long.

This isn’t great news for the stability of the ice shelf. Water is heavy, and the weight can cause the ice below these lakes to crack. As glaciologist Alison Banwell wrote in a separate analysis of the studies for Nature, “If a lake suddenly drains through a crevasse to the ocean below, the load deficit from the ice shelf’s surface can induce more crevasses, potentially triggering a chain reaction” of draining lakes. “This process might have been responsible for the large-scale break-up of Antarctica’s Larsen B Ice Shelf in 2002, when more than 2000 lakes drained in just a few days.”

All that water ends up in the ocean, contributing to rising sea levels. As NASA geophycisist Ala Khazendar told NPR in January, "Ice shelves are very important. They are the gates of Antarctica in a way, and the gatekeepers of Antarctica." The National Snow and Ice Center estimates that if the Antarctic Ice Shelf—which covers 98 percent of the continent—melted, sea levels would rise by as much as 200 feet.

All that makes meltwater a little worrisome for climate scientists, but there may be a silver lining, at least according to one of the published papers.

One river network the researchers studied ends in a 427-foot-wide waterfall that can empty the entire amount of meltwater produced by the ice shelf annually in just seven days. That may make the ice shelf more stable, since the meltwater gets funneled into the ocean immediately instead of building up on top of the ice shelf and cracking the ice below. “Export of meltwater by surface rivers may buffer the impact of warming temperatures,” the researchers wrote. At least when it comes to breaking up ice sheets. Unfortunately, those drainage systems are still really effective at sloughing off water into the ocean, which will still affect sea level rise.

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NOAA Suomi-NPP/University of Oxford/Simon Proud
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As Predicted, a Massive Iceberg Just Broke Off in Antarctica
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NOAA Suomi-NPP/University of Oxford/Simon Proud

Well, it finally happened. As Mental Floss reported last week, the last few decades have seen dramatic changes to the Larsen ice shelf, most recently with a growing rift along the section called Larsen C threatening to entirely break off. This week, it finally split, creating an iceberg the size of Delaware. At more than a trillion tons, it's one of the largest icebergs ever recorded.

The sections called Larsen A and B collapsed in 1995 and 2002, respectively, effectively reshaping the coastline of the Antarctic Peninsula.

The Larsen C crack spread slowly—you might say glacially—at first. But by June 2017, it was cruising right along, widening at a pace of about 32 feet per day. Experts at Swansea University’s Project Midas, which monitors the ice shelf, predicted the break would come within "hours, days, or weeks."

It took about a week. New imagery from NASA’s Suomi National Polar-orbiting Partnership (NPP) satellite shows a distinct split in the ice shelf.

"The rift was barely visible in these data in recent weeks," Adrian Luckman of Swansea University told the BBC, "but the signature is so clear now that it must have opened considerably along its whole length."

The precise cause of the split remains to be seen. While climate change is responsible for melting sea ice around the world, experts say this particular break may have been inevitable.

"We know that rifts like this periodically propagate and cause large tabular icebergs to break from ice shelves, even in the absence of any climate-driven changes," Chris Borstad, of the University Centre in Svalbard, told the BBC. "I am working with a number of colleagues to design field experiments on Larsen C to answer this specific question (by measuring the properties of the Joerg suture zone directly). But until we get down there and take some more measurements, we can only speculate."

[h/t BBC]

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John Sonntag, NASA // Public Domain
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An Iceberg the Size of Delaware Is About to Break Away From Antarctica
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John Sonntag, NASA // Public Domain

The crack in the Antarctic ice has been growing for years. Now scientists say a major break is coming—an event that could set in motion the disintegration of the entire 19,000-square-mile Larsen C ice shelf.

The entire Larsen ice shelf, comprising Larsen A, B, C, D, E, F, and G, wraps like a crumbling white blanket around the Antarctic Peninsula. The rift in Larsen C started small, as these things do, but with each passing day its expansion accelerates. By June 24, the crack was widening by about 32 feet per day.

Aerial shot of a rift in the Larsen C ice shelf.
John Sonntag, NASA // Public Domain

Scientists at the UK-based Project MIDAS say a big break is imminent. "We still can't tell when calving will occur," they wrote on their website, "it could be hours, days or weeks—but this is a notable departure from previous observations."

The loss of the Delaware-sized iceberg—one of the largest ever recorded—will be both dramatic and destabilizing for its parent ice shelf.

"When it calves," the researchers write, "the Larsen C Ice Shelf will lose more than 10 percent of its area to leave the ice front at its most retreated position ever recorded. This event will fundamentally change the landscape of the Antarctic Peninsula."

It could also trigger Larsen C's total collapse into the sea, which could, in turn, raise worldwide sea levels by four inches.

The break will be the third major calving from the Larsen ice shelf in recent memory. The area called Larsen A collapsed in 1995, followed by Larsen B in 2002. The latter was double the size of greater London.

The researchers have no evidence directly linking this particular break to climate change, but as a press statement noted, "It is widely accepted that warming ocean and atmospheric temperatures have been a factor in earlier disintegrations of ice shelves elsewhere on the Antarctic Peninsula."

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