As Antarctic ice shelves shrink, 'shelfwatchers' await major break-off
A huge iceberg is likely to soon break off from the Larsen C Antarctic ice shelf. Although break-ups themselves don't contribute to sea rise, they can indirectly increase it.
A huge iceberg is likely to soon break off from the Larsen C Antarctic ice shelf. Although break-ups themselves don't contribute to sea rise, they can indirectly increase it.
Sometime in the 1960s, a tiny crack emerged in Antarctica鈥檚 Larsen C ice shelf. Today, it鈥檚 more than 100 miles long, two miles wide in places, and growing at a rate of five football fields per day. Only 12 miles now connect the soon-to-be iceberg to Larsen C.
Several media outlets, including 海角大神, have been on 鈥渟helfwatch鈥� for months, as scientists expect an iceberg the size of Delaware to break off from Larsen C in the near future. That would mark one of the largest such events on record, joining similar break-offs from Larsen A and B. Almost 600 square miles of ice separated from Larsen A in 1995, and in 2002 more than 1,200 square miles broke from Larsen B, whose shrinkage is captured in a new satellite image.
The breakup itself likely won鈥檛 contribute to sea level rise, however, "as the Larsen C shelf already floats in the ocean," as the Monitor's reported last month. "It can't affect water levels any more than a melting ice cube can cause a glass to overflow."
But scientists say聽the collapse of ice shelves can indirectly drive sea level rise.
鈥淵ou can think of the Larsen or really any ice shelf like it is a cork in the neck of a champagne bottle lying on its side,鈥澛爏cientist Christopher Shuman聽explained in a NASA release.
Ice shelves sit over the ocean, but are fed by land-based glaciers. They also keep those glaciers from flowing directly into the sea.
鈥淥nce you pop that cork,鈥� Dr. Shuman continued, 鈥渢he wine inside 鈥� all that glacial ice sitting on land 鈥� will start flowing out. And that鈥檚 worrisome because such thinning land ice is directly increasing global sea levels.鈥�
That鈥檚 not the only way that collapses like these encourage sea level rise, though. When ice shelves or glaciers melt, they flood the ocean surface with cold fresh water that doesn鈥檛 mix very well with lower levels of the ocean.
As a result, the ocean becomes 鈥渟tratified,鈥� with a cold surface and relatively warm lower levels. This, in turn, means that glaciers exposed to the ocean face greater heat below the surface, in addition to warmer air temperatures, leading to stronger melt.
Some 14,000 years ago, this process caused the rapid breakup of Antarctica鈥檚 ice sheets and a nearly 10-foot rise in sea level, according to a study published in January by scientists at Australia鈥檚 University of New South Wales. And global warming may have created the right conditions for those changes to happen again.聽
This rapid melting has an ironic side effect: As the ocean surface around Antarctica gets colder and fresher, the actual sea ice expands. NASA observed 鈥渢hree record high extent years鈥� of sea ice from 2012 to 2014.
But this expanded sea ice cover doesn鈥檛 mean Antarctica鈥檚 stressed glaciers will get a reprieve. 鈥淪ea ice formation is a function of sea surface conditions but the water that rapidly melts glaciers is often found below several hundred meters of water,鈥� geophysicist Dr. Jamin Greenbaum told The Washington Post in 2015, adding that 鈥渋ncreased sea ice extent doesn鈥檛 necessarily have a direct effect on coastal glacier melting.鈥�