On July 12, 2017, a giant block of ice was definitely separated from one of the ice shelves that make up the Antarctic coast. This is the A-68 iceberg.

This new iceberg is one of the largest that the world has ever known, with 5,800 km². Its split from the Larsen C platform is a new scenario of vulnerability to future episodes such as the one we are narrating.

More than a decade ago scientists at Swansea University were tracking a large rift that began to accelerate its development from 2014, until finally the block broke off.

The MIDAS Project has been responsible for carrying out this observation through satellite imagery, such as NASA’s Aqua MODIS. Thanks to these orbital instruments, the research team was able to capture the presence of water in the crevasse that made its way along the Larsen C platform, parallel to the coast. An unequivocal sign of detachment.

1. Larsen C Ice Shelf and the A-68 iceberg. Source: modis.gsfc.nasa.gov.

Now, an iceberg slightly larger than Norfolk, 200 meters thick, will begin to drift. It will be swept away by the ocean currents of the Weddell Sea. However, this process will take many years and for the moment any prediction will be made based on past events in the same southern region.

In this way, the Antarctic Peninsula continues to modify its coastline and reduce its extent. The A-68 is just one of the icebergs that have been separating from the ice shelves of Antarctica.

Ice Platforms: The Origin of Icebergs

Ice shelves are the extent of continental glaciers on the sea surface. Currently we can find them in northern Canada, Greenland and Antarctica. They are the result of the flow of the continental ice mass towards the coast. Its outer edge has vertical walls up to 30 meters high, which is why the first explorers called it “The Great Barrier”.

2. Dimension of the ice shelf compared with the ice sheet. Source: antarctica.gov.au

These vertical walls arise, as in the case of the iceberg A-68, by the detachment of large glacial blocks from the original platform, which usually show signs of instability when floating in water.

This, added to the increase of the temperatures of the last years, generates tensions and efforts provoked by its own weight and favors the appearance of crevasses that inevitably lead to the formation of icebergs.

Here are some of the largest ice shelves in Antarctica:

  • Ross
  • Ronne-Filchner
  • Amery
  • Shackelton
  • George VI
  • Wilkins
  • Larsen
  • Riiser-Larsen
3. Existing ice shelves in Antarctica. Source: nsidc.org

The fate of the A-68 iceberg and the Larsen C platform

With a weight of more than one gigaton (1000 million tons), one of the great concerns was that the detachment of the iceberg A-68 increased the level of the sea. Fortunately, the Project MIDAS research team does not believe that it occurs, because the frozen block was already in a state of flotation before the fracture.

Once left, the new iceberg may take years or decades to move away from the Antarctic shores, although it is always difficult to predict. According to other past events, the sea currents of the Weddell Sea could drag A-68 to South Georgia Island.

There, the immense block would run aground due to the smaller depth of the continental shelf that surrounds the island (remember that the iceberg A-68 has a thickness of approximately 200 meters). Once stranded, its destiny would be its fusion and fragmentation into smaller blocks.

4. Marine currents in the Antarctic environment. In red, the origin of the iceberg A-68. In yellow, South Georgia Island. Source: teara.govt.nz

A disruption of the food chain cycle

But this situation has a major impact on the marine ecosystem, according to Eugene Murphy, member of the British Antarctic Survey, which has altered the cycle of the food chain.

As with several icebergs known as A-38, A-22B or B-10A, melting ice in the surrounding area would bring a lot of fresh water to a marine environment. This would modify the circulation of the currents in the platform due to the change in the density of the water.

It is true that it would also carry a volume of rocky sediments from the Antarctic continent, which are a source of nutrients essential for the growth of seaweed and diatoms.

But the worst thing is that an iceberg aground of these dimensions would block the arrival of krill. It is a tiny crustacean that is key to the food chain. Its appearance is associated to the usual marine currents in the island’s surroundings.

Segment C of the Larsen Platform could be regenerated

Meanwhile, the Larsen C segment of the Larsen Platform (in honor of Norwegian captain Carl A. Larsen) has already seen its area reduced by 12% following the separation of the A-68 iceberg. Professor Adrian Luckman, principal investigator of the MIDAS Project, points out that the ice sheet could gradually regenerate if the temperature pattern in Antarctica stops rising.

Luckman also believes he could suffer further crashes, which would lead the Larsen C segment to collapse, as has already happened with segments A and B in 1995 and 2002, respectively.

5. Segments of the Larsen Platform and its loss of ice between 1960 and 2008. Source: pri.org

In turn, Luckman adds that they can not assure that this new detachment is a direct consequence of the Climate Change produced by the human being. But he warns that if the Larsen C segment loses more surface in the future, glacier melting in the Antarctic Peninsula would accelerate and could have serious implications for rising sea levels.

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