ANTARCTIC ICE ON THE DECLINE

 

ANTARCTIC ICE ON THE DECLINE

                                                                                     Nikunja Bihari Sahu

           The icy continent Antarctica is ringed by a number of ice shelves, which are large, thick floating extensions of glaciers that extended from the land into the sea. Built up due to snowfall over a vast time period, these shelves are now vulnerable to surging  air temperatures and warming ocean waters, which can cause them to thin, break off to pieces at  unusual rate, and even collapse. The ice left behind them is liberated to flow more rapidly into the ocean as water, raising the seas causing a world-wide concern.

           In a recent development (in the week beginning from 10^th July, 2017), one of the largest icebergs on record has broken away from an ice shelf in Antarctica.   This was reported by the researchers who have been monitoring a huge crack i the vulnerable  Larsen C Ice Shelf . The iceberg measuring about 5800 sq. km. in area and weighing more than a trillion ton has been let loose from the ice shelf into the nearby sea.

              The break was detected by a NASA’s instrument MODIS on the Aqua satellite and was confirmed by the European Space Agency.

            Before the break, a rift across the Larsen C ice shelf had developed over more than 100 miles in length leaving only just a few miles of remaining ice connecting   the nascent iceberg to the shelf. The break began several years ago but had quickened its advance in the last year, increasingly convincing scientists that the iceberg detachment was inevitable, despite the fact the prevailing season was winter in Antarctica.

 VAST ICE LOST

      The iceberg is one of the largest recorded in history. It contains 4 times   as much water as lost by the Greenland Ice sheet per year. Even larger icebergs than this have broken off in Antarctica in the past including a berg of over 4,000 square miles (dubbed as B 15) in 2000. That was almost twice the size of Larsen C and broke off the Ross Ice Shelf, Antarctica’s largest floating ice body. It was the biggest iceberg ever recorded.

            Larsen C also lost an even larger piece in 1986, but that occurred in considerably different circumstances. It came after the shelf had grown considerably and extended much farther out into the Weddell Sea than it does now.

     If we add up all the ice lost from the various Larsen ice shelves since the 1970s, it is around 7,350 square miles which is approximately equivalent to the state of New Jersey.

TRACKING

        Scientists will track the iceberg using satellite imagery and should be able to get regular glimpses even during the Antarctic night aided by   radar and thermal imaging techniques. Its future progress is difficult to predict. It may remain in one piece but is more likely to break into fragments. Some of the ice may remain in the area for decades while parts of the iceberg may drift north into warmer waters where it will eventually melt down before losing its identity in the vast expanse of the sea water for ever.  

        The iceberg’s progress is expected to be northward in the direction of South America. First, it will be swept up in the Weddell Sea Gyre, an elongated circuit of ocean flow, and then should pass to the west of South Georgia and the South Sandwich Islands.  Then the iceberg, or its pieces, will become swept up in the Antarctic Circumpolar Current which encircles the entire continent, flowing in a west-to-east direction.

      GLOBAL WARMING LINK

          Opinions are divided whether the break is part of a natural process or something related to the recent climate change.  Scientists don’t have all the data to conclude whether the floating Larsen C ice shelf was affected by the air temperatures above it or the ocean temperatures below it ruling out the global warming link.

         However, some scientists are skeptical.  Antarctica’s ice shelves do indeed calve large pieces regularly in a natural process. As Larsen C is the third in a row to collapse after the Larsen A and Larsen B ice shelves in quick succession, the global warming link becomes more apparent.C

CONSEQUENCES

1.      1. The  change is so large that it will trigger a redrawing of the Antarctic coastline. 

2.     2. The  Larsen C ice shelf, previously the fourth largest of its kind in Antarctica, is now reduced to the fifth or sixth position due to the recent loss of ice.

 3.     The iceberg contains so much mass that if all of it were added anew to the ocean, it would actuate almost 3 millimeters of global sea level rise. However, because the ice was already floating, there won’t be a substantial sea level rise.

 4.     The   loss could speed up the outward ice flow of the remainder portion of the Larsen C ice shelf, which would eventually increase sea level.

 5.     The effect of the break is to shrink the size of the floating Larsen C ice shelf by 12 percent. This could have a destabilizing effect on the remainder of the shelf, which is among Antarctica’s largest.

 6.     The loss of vast amount of ice from the planet will mean reflection of less amount of the Sun’s radiant heat to space and absorption of more heat by the sea water resulting in the more melting down of ice. This would accelerate the global warming process on the planet which would further hasten the Antarctic ice melt and thus a never ending vicious cumulative cycle would go on.

 LARSEN ICE SHELF

       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 from Cape Longing   to the area just southward of Hearst Island . In 2005, it covers approximately 78500 km² of the earth's sea with exceptionally thick ice. 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.  In finer detail, the Larsen Ice Shelf is a series of shelves that occupy (or occupied) distinct embayment  along the coast. From North to South, the segments 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 identified.

          The disintegration of the ice shelf since the mid1990s has been widely reported with the collapse of Larsen A in 1995 and Larsen B in 2002. Now, the break-up of  Larsen C leads us to speculate a day, not far from now, when the entire Antarctic region will become ice free leading to a worldwide catastrophe.

 

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                                                                          Regional Science Centre

                                                                                      Bhopal

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LARSEN C ICE SHELF BEFORE COLLAPSE

RIFT DEVELOPED IN LARSEN C ICE SHELF

LARSEN C ICE SHELF IN ANTARCTICA

MECHANISM OF COLLAPSE OF THE  ICE SHELF