4 November, 2020

An iceberg is heading towards the sub-Antarctic island of South Georgia. A68a – the size of the UK county of Somerset – broke off from the Larsen C ice shelf in 2017 and has been drifting north ever since. If it becomes grounded near the island, it could cause disruption to the local wildlife that forage in the food-rich ocean.

A close up of a snow covered mountain
The A68 iceberg looks like a pointed finger. It is 400km off the coast of South Georgia. Credit: Copernicus Sentinel 3 Mosaic / Polar View

Professor Geraint Tarling, an ecologist at British Antarctic Survey, says:

“Ecosystems can and will bounce back of course, but there’s a danger here that if this iceberg gets stuck, it could be there for 10 years. An iceberg has massive implications for where land-based predators might be able to forage.

“When you’re talking about penguins and seals during the period that’s really crucial to them – during pup- and chick-rearing – the actual distance they have to travel to find food (fish and krill) really matters. If they have to do a big detour, it means they’re not going to get back to their young in time to prevent them starving to death in the interim.

“However, the iceberg does bring benefits if it remains in the open ocean. It carries enormous quantities of dust that fertilise the ocean plankton in the water that cascades up the food chain. This plankton also draws in carbon from the atmosphere, partially offsetting human CO2 emissions.”

Killer whales, South Georgia
Large numbers of whales, seals and penguins feed off the coast of South Georgia. Photo credit: Martin Collins

Although satellite imagery suggests A68a could be on a direct path for South Georgia, it could continue north.

“Whether it grounds and gets stuck or drifts past the island is in the balance”, says BAS remote-sensing and mapping specialist Dr Peter Fretwell.

“The currents should take it on what looks like a strange loop around the south end of South Georgia, before then spinning it along the edge of the continental shelf and back off to the northwest. But it’s very difficult to say precisely what will happen.”

BAS Remote Sensing Manager Andrew Fleming said a request was going into the European Space Agency for more satellite imagery, particularly from its pair of Sentinel-1 radar spacecraft.

He says: “A68a is spectacular. The idea that it is still in one large piece is actually remarkable, particularly given the huge fractures you see running through it in the radar imagery. I’d fully expected it to have broken apart by now. If it spins around South Georgia and heads on northwards, it should start breaking up. It will very quickly get into warmer waters, and wave action especially will start killing it off.”