Tracking an ice giant

Between July 10-12 of this year an iceberg four times the size of London broke off from the Larsen C ice shelf in Antarctica. The 5,800km2 iceberg, dubbed A-68, weighs in at one trillion tonnes, making it one of the biggest icebergs ever recorded.

Since breaking off, A-68 continues to float around Antarctica’s Weddell Sea.

Where it will end up nobody knows.

The birth of A-68

Although a crack on the west coast of the Larsen C ice shelf, on the Antarctic Peninsula, had been forming for around a decade, it wasn’t until late 2010 that scientists first started to take notice of it. Back then, it was about a third of its final size. After 2010, the crack slowly crawled northward up the ice sheet until late 2015, when it extended about 150km. Then things got interesting.

An Antarctic iceberg. Photo from Wikimedia Commons (licensed under CC by 2.0)

In 2016 the crack accelerated throughout the year. When we rang in the new year in 2017, it had grown as much in one year as it had the previous five. And it didn’t stop there. January and February of 2017 saw even faster growth as the crack pushed further north.

Then, in a dramatic turn of events, in May of this year, it suddenly turned west and began to beeline right towards the coast.

Now scientists began to predict the imminent calving (the scientists word for break-off) of one the biggest icebergs ever seen. In early June, just 13km separated the crack from the coast of Antarctica.

At this time of year Antarctica is plunged into what’s known as the polar night. There is no sunlight, making monitoring the giant crack a challenge. Luckily, satellite images using infrared sensing techniques to penetrate the gloom were able to pick up black and white images of the ice shelf. As winter progressed and the crack moved closer to open water, these images revealed a web of cracks emerging from the main fissure. As June turned into July scientists were expecting the calving any day.

Finally, after weeks of anticipation, some time between July 10-12 the crack finally reached the coast and A-68 (so named by the National Ice Center) was born.

As daylight slowly begins to return to the end of the earth, pictures of the massive iceberg are appearing, and it looks as though it’s already beginning to break up.

The big picture

Scientists have been quick to make clear that calving events such as this one are not uncommon in glaciated environments. There is no clear evidence at the moment linking this event to climate change, although it has been compared to the disintegration of both the Larsen A and B shelves, which were strongly linked to man-made warming.

Satellite image of the calving of A-68. Adapted from Earth Observatory, NASA

Although, the Larsen ice shelves float on the surface of the ocean, they are attached to the main glaciated landmass of Antarctica. Since they are already floating on the sea they have no direct effect on sea levels. They are, however, important in acting as a buttress holding back the main glacier. Glaciers are like slow-moving rivers; they flow gradually out towards the sea. Floating ice shelves like the Larsen family block their flow and restrict sea level rise. If Larsen C follows the path of its cousins and continues to disintegrate there could be massive consequences for sea levels.

So although ice loss on this scale occurs naturally over long periods of time, if events such as this one keep occurring, it’s only a matter of time before irreversible damage is done.

4 Responses to “Tracking an ice giant”

  1. Dominic Thorn says:

    Thanks for the comments! The collapse of the Larsen A and B ice shelves were closely linked to climate change, so it looks as though lots more of these events could be on the cards.

  2. scripps says:

    Interesting blog! I wonder if more cracks will appear at an accelerating rate due to climate change.

  3. mwatchorn says:

    The progression of the crack and the enormity of the iceberg are difficult to comprehend. I guess events of this size and scale need hindsight to be fully appreciated.

  4. Ellen Rochelmeyer says:

    Fascinating! I had no idea people were watching the ice shelves so closely as to monitor and predict the’calving’ of icebergs. ‘Calving’- a great word for it.