Ice Shelf Bigger Than Manhattan Could Be About To Break From Antarctica

IFLScience!
March 15, 2016
Robin Andrews

photo credit: Nansen Ice Shelf and the crack, taken by Landsat 8 on December 16, 2015. USGS


Antarctic scientists have documented ice shelves disintegrating from the southern continentat an unprecedented rate, thanks in no part to the pace of man-made climate change. The icy realm’s next victim may be the Nansen Ice Shelf, through which resides a ginormous crack that threatens to cleave it off at a moment’s notice.

As spotted by the United States Geological Survey's (USGS) Landsat 8 satellite, Nansen – which at 1,750 square kilometers (600 square miles) in size is twice the size of Manhattan Island – is suffering the fate of many ice shelves in recent history. The current stability of Antarctic ice shelves, which are the floating seaward extensions of ice sheets, is hazardously low. Increased global temperatures are causing the undersides of huge ice masses to melt and weaken.

Consequently, Larsen-A in the Antarctic Peninsula collapsed in 1995, followed by Larsen-B in 2002. Larsen-C, which is 2.5 times the size of Wales, is treading on thin ice. Nansen, which is “fed” by the Priestly and Reeves Glaciers and backsup against the peculiar-looking Drygalski Ice Tongue, is looking decidedly wobbly: Two years ago, the crack was barely visible, whereas now it spans almost the entire length of the ice shelf.

“The front of Nansen Ice Shelf… looks ready to calve off into a tabular iceberg,” wrote Ryan Walker, a researcher at NASA Goddard, on a blog for NASA’s Earth Observatory. “There’s a huge crack, miles long and sometimes over a hundred yards wide, which runs more or less parallel to the front of the ice shelf.”

Although this may sound rather catastrophic, there are two points worth considering here. Firstly, ice shelves make up around 75 percent of the Antarctic coastline, and their total combined area is equivalent to 1.56 million square kilometers (603,000 square miles). If all of Nansen collapses, it will reduce Antarctica’s ice shelf coverage by just 0.1 percent.



The mega crack, photographed in December 2015. Christine Dow/NASA Goddard


Nansen doesn’t even register as a “major” ice shelf, with those such as Ross, at around 472,000 square kilometers (182,000 square miles), dwarfing it. The Ross Ice Shelf partly collapsed at the end of the last ice age around 10,000 years ago, when a colossal chunk280,000 square kilometers (108,000 square miles) in size fell into the sea over 1,500 years. That’s 360 times the size of Manhattan Island, by the way.

Secondly, these ice shelves may be anchored to the land, but they do not actually significantly contribute to sea level rise – after all, they’re already floating on the sea. So the collapse of Nansen by itself won’t cause much harm, per se.

However, ice shelves like Nansen do act as vast barricades for glaciers behind them. When an ice shelf is removed, glaciers begin to tumble into the sea at surprisingly fast speeds – sometimes moving ten times faster than normal – and these will definitely cause the sea level to rise. So in effect, man-made climate change is breaking Antarctica’s huge ice dams.

Although the Antarctic winter is now setting in, strong winds can prevent the nearby water from freezing up into ice, meaning that we might not have to wait until the summer to see Nansen’s epic break-up.