WEATHER & CLIMATE EARTH

Collapse of Larsen Iceshelf in Antarctica

The Larsen Ice Shelf is a long ice shelf in the northwest part of the Weddell Sea, extending along the east coast of the Antarctic Peninsula. It is named after Captain Carl Anton Larsen, the master of the Norwegian whaling vessel Jason, who sailed along the ice front as far as 68°10' South during December 1893. From north to south, the segments of the ice-shelf are called Larsen A (the smallest), Larsen B, and Larsen C (the largest) by researchers who work in the area. Further south, Larsen D and the much smaller Larsen E, F and G are also named.
The breakup of the ice shelf since the mid 1990s has been widely reported, with the collapse of Larsen B in 2002 being particularly dramatic. The figure shows how Larsen systematically receded over the years, from 1998 onwards, leaving behind a small remnant seen in the bottom of the map. The breaking up of the ice-shelf is due to undue warming at the location, due to anthropogenic global warming, or man-made global warming.
The processes around an Antarctic ice-shelf that causes it to break up are shown in the schematic figure. Larsen A shelf, which was the furthest north (in fact it is outside the Antarctic Circle), had previously broken up and reformed only about 4,000 years ago, before finally breaking up in 1995. The former Larsen B had been stable for at least 10,000 years. Despite its great age, the Larsen B was clearly in trouble at the time of the collapse. With warm currents eating away the underside of the shelf, it had become a "hotspot of global warming." What especially surprised glaciologists was the speed of the breakup, which was a mere three weeks (or less).
Factors they had not anticipated were the powerful effects of liquid water; ponds of meltwater formed on the surface during the near 24 hours of daylight in the summertime, then the water flowed down into cracks and, acting like a multitude of wedges, levered the shelf apart.
The oldest ice on the current shelf dates from only two hundred years ago. Larsen C is the fourth largest ice shelf in Antarctica, with an area of about 50,000 square km.
In 2004, a report concluded that although the remaining Larsen C region appeared to be relatively stable, continued warming could lead to its breakup within the next decade. News reports in the summer of 2016 suggested that this process has begun. On November 10, 2016, scientists photographed the growing rift running along the Larsen C ice shelf, showing it running about 110 kilometres long with a width of more than 91 m and a depth of 500 m.
A colossal crack in this ice shelf abruptly grew by 18 kilometers during the second half of December 2016. (That was the height of the region's summer.) Members of Project MIDAS, an Antarctic research group, reported the crack's dramatic growth on January 5. This separating ice is now only about 20 kilometers from Larsen C’s edge.
Ice sheets and glaciers
Satellite images in 2014 revealed that a crack in Larsen C rapidly extended across the ice shelf. If the crack reaches the ice shelf’s edge, it could snap off a large area of ice; this is called calving. This will reduce Larsen C’s size by about 10 percent. That’s enough to shrink the shelf to its smallest size in recorded history. And it could potentially kick start the shelf’s disintegration.
Daniela Jansen is a glaciologist at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. She led the 2015 study. At that time, she had expected the crack might chip apart Larsen C within five years. “We should keep a close eye on Larsen C,” she had argued. “It might not be there for so much longer.” Larsen C covers about 55,000 square kilometers. That makes it the largest ice shelf along the Antarctic Peninsula. Since Larsen C’s ice already floats in the ocean, the big break-off won’t immediately raise sea levels. If all the ice that the Larsen C shelf currently holds back were to enter the sea, it is estimated that global waters would rise by 10 cm.
The scientists can’t say for certain when Larsen C will break off. But they think it could be soon. Usually, researchers camp on the shelf during the Antarctic summer to conduct their science. But this year, the British Antarctic Survey announced it would halt this practice. Scientists will still be allowed access to the area. But they will be restricted to day trips only — with rescue aircraft waiting nearby.