Drifting away: huge Antarctic iceberg on the move

Earlier this week, polar scientists focusing on the Larsen C ice shelf in the Antarctic Peninsula witnessed the movement of a huge, trillion-tonne iceberg out into the Weddell Sea, and towards the South Atlantic Ocean.

The iceberg, named A-68, is one of the largest icebergs ever recorded by Antarctic experts: at 6000 square kilometres, it is four times the size of Greater London and roughly a quarter the size of Wales.

The gigantic iceberg first broke off from the Larsen C ice shelf in July of this year, when a US satellite took pictures of the rift between A-68 and the ice shelf, during the iceberg’s ‘calving’. The area has been monitored for over a decade, with scientists expecting the large crack in the shelf to open up considerably. Since July, the iceberg has been rocking slowly back and forth, but a Spanish satellite confirmed on September 22nd, that the iceberg is being carried out into the Weddell Sea by currents.

Experts predict that the ‘megaberg’ will be swept northwards and into the current that surrounds the southernmost continent – the ACC, or Antarctic Circumpolar Current. From there, it is likely that A-68 will follow in the flow of one of its megaberg predecessors, A-38, which was carried north to South Georgia, to a patch of sea known as ‘the Graveyard of the Icebergs’.

When megabergs reach the island of South Georgia, they often make ground, and slowly decay, splitting up into smaller icebergs, or melting, and adding considerable amounts of freshwater to the sea around the island – this melting can have huge impacts on the area, both positive and negative.

Sometimes, a melting iceberg will release trapped nutrients that feed algae and diatoms, tiny organisms at the bottom of the polar food web. However, large icebergs can often block an inflow of tiny sea creatures called krill, into the area surrounding South Georgia, and this can have devastating effects on the wildlife.

Krill are an essential source of food for a variety of animals found in the Antarctic Circle, from penguins to whales, and any decrease in the amount of krill in the sea has a knock-on effect on the amount of seals, penguins and Antarctic birds in the area: scientist find that the years in which krill inflow is blocked, starved seal pups are often found ashore.

It is not yet clear if the A-68 megaberg will even make it as far as South Georgia, however. Recent images from the Spanish Deimos-2 spacecraft already show that the iceberg is losing the sharp edges it once had, showing fragmentation already beginning at the edges of the megaberg. All smaller chunks of ice breaking from A-68 are being named A-68b, A-68c, A-68-d, and so on – these are likely to continue floating close to A-68, but may be separated from their parent iceberg, to become anchored in shallower waters, to become ‘ice islands’ in the Weddell Sea.

Scientists are currently monitoring both the megaberg and the Larsen C ice shelf, to see if there is any further fracturing of the ice.

As A-68 moves clear of the ice shelf and out to sea, the section of seafloor it has cleared is now an area of scientific interest. The area has already gained a protected status that prevents any fishing activity for the next two years, leaving it solely for scientific study. As the Antarctic spring began earlier this week, numerous scientific groups have begun to plan research projects in the area for the Antarctic summer, in the hope that the depths now exposed by the megaberg might reveal new Antarctic species.