As expected, an iceberg half the size of Jamaica has finally cut itself loose from Antarctica's Larsen C Ice Shelf. Dubbed A68, the 5,800 square km chunk of ice one of the biggest ever recorded -- but what happens now, both to the iceberg and the ice shelf, is anyone's guess.
The calving event was confirmed by NASA's Aqua MODIS satellite instrument and by the ESA's Copernicus Sentinel-1 mission. The ESA is currently anticipating a second pass of Sentinel1 over the site to make doubly sure.
NASA MODIS thermal image from 12 July 2017.
The fissure that had been growing for years finally reached the sea sometime between July 10 and July 12, releasing the overbearing chunk of ice into the ocean. The calving event itself wouldn't have been dramatic to an observer, as the tremendously heavy iceberg will now slowly make its way north into the Weddell Sea. A68 contains twice the volume of water as Lake Erie, but it won't contribute to rising sea levels because it's already displacing a huge amount of sea water.
The question now is what'll happen next. The Larsen C Ice Shelf has now been reduced by more than 12 per cent, and the complexion of the Antarctic Peninsula has been altered, perhaps forever. The remaining ice shelf is expected to grow in the coming years, but research from Swansea University suggests the region is now more precarious and less stable. There's a good chance that Larsen C may follow in the footsteps of its neighbour, Larsen B, which collapsed following a similar calving event in 2002.
NASA Suomi VIIRS panchromatic image from July 12 2017, confirming the calving.
"We have been anticipating this event for months, and have been surprised how long it took for the rift to break through the final few kilometres of ice. We will continue to monitor both the impact of this calving event on the Larsen C Ice Shelf, and the fate of this huge iceberg," said Adrian Luckman, lead investigator of the UK-based Project MIDAS, which has been monitoring the iceberg closely over the past few months.
As for the iceberg itself, it's now one of the largest ever recorded, and its fate is difficult to predict. Luckman says it may remain in one piece, but it's 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," he said in a statement.
There's a temptation to ascribe this rare and dramatic calving event to climate change, but scientist have been at great pains to point out that this is very likely a natural occurrence. This is what ice shelves do -- they grow until the point of collapse, and then the cycle repeats itself. Writing in The Conversation, Luckman explains:
This event has also been widely but over-simplistically linked to climate change. This is not surprising because notable changes in the earth's glaciers and ice sheets are normally associated with rising environmental temperatures. The collapses of Larsen A and B have previously been linked to regional warming, and the iceberg calving will leave Larsen C at its most retreated position in records going back over a hundred years.
However, in satellite images from the 1980s, the rift was already clearly a long-established feature, and there is no direct evidence to link its recent growth to either atmospheric warming, which is not felt deep enough within the ice shelf, or ocean warming, which is an unlikely source of change given that most of Larsen C has recently been thickening. It is probably too early to blame this event directly on human-generated climate change.
Now all this doesn't mean that climate change isn't relevant to this story. What happens next -- both to the ice sheet and the new iceberg -- could definitely be influenced by warmer waters, changes to wind and water flow patterns, and so on. In a way, the story of the Antarctic Peninsula, Larsen C, and its new baby A68, has only just begun.
NASA has released an incredible new thermal perspective of the new iceberg, and a GIF showing the fissure as it grew over time.
A thermal wavelength image of the iceberg. Darker colours are colder, and brighter colours are warmer, so the rift between the iceberg and the ice shelf appears as a thin line of slightly warmer area.(Image: NASA Worldview)
Animation of the growth of the crack in the Larsen C ice shelf, from 2006 to 2017, as recorded by NASA/USGS Landsat satellites. (Image: NASA/USGS Landsat)