TORONTO -- It was a near-miss of gigantic proportions.
The A-74 iceberg, which is about twice the size of Toronto, recently crashed into part of Antarctica, in what the European Space Agency (ESA) describes as a 鈥榤inor impact.鈥�
If the collision had been more severe, another huge iceberg could have calved, or broken off of, the Brunt Ice Shelf on the western coast of the continent.
鈥淭he nose-shaped piece of the ice shelf, which is even larger than A-74 remains connected to the Brunt Ice Shelf, but barely,鈥� Mark Drinkwater, an ESA geophysicist, said in dated Aug. 20. 鈥淚f the berg had collided more violently with this piece, it could have accelerated the fracture of the remaining ice bridge, causing it to break away.鈥�
The A-74 iceberg, which at 1,270 square kilometres is one of the largest in the world, originally split from the ice shelf in February and had been drifting nearby until easterly winds caused it to shift its course from Aug. 9 to Aug. 18.
The Brunt Ice Shelf was home to the British Antarctic Survey鈥檚 Halley VI Research station until 2017, when it was deemed unsafe. The team then moved their station about 20 kilometres away from Chasm 1, a large crack running northwards from the southernmost part of the ice shelf.
The ESA plans to continue to monitor the situation using Sentinel satellite imagery.
They aren鈥檛 the only ones watching.
David Long and his students run the Antarctic Iceberg Tracking Database (AITD) at Brigham Young University in Provo, Utah. They鈥檙e tracking 51 active Antarctic icebergs.
鈥淚ce in Antarctica is a bellwether for global climate change,鈥� Long said by email on Thursday. 鈥淎s the oceans warm, the major floating ice sheets and glaciers melt from beneath and become unstable. This can lead to their breakup and the rapid release of land glacial ice stored behind them. This release will cause sea levels around the world to rise.鈥�
While the calving of the Brunt Ice Shelf may allow the land glaciers to flow more rapidly to the sea and increase the global sea level, the minor incident with theA-74 iceberg is not a particular concern for the area, he said.
Scheridan Cloward, the AITD's lead data analyst, is currently in charge of the real-time tracking of A-74. She said it鈥檚 following the polar current around Antarctica, which is to be expected.
鈥淎-74 is in the area of the Weddell Sea, which we lovingly call 鈥業ceberg Alley,鈥� as the combination of the polar currents and the Antarctic Peninsula create a thoroughfare for icebergs to pick up speed and make their way out towards open ocean,鈥� she said by email on Thursday.
鈥淭he brief touch with the other point of the Brunt Ice Shelf is the impressive part,鈥� Cloward said. 鈥淭he fact that A-74 barely touched the other ice shelf without causing breakage or calving is notable. In contrast, D-28 collided with an ice shelf back in June of this year and caused five new icebergs to calve.鈥�
The A-74 iceberg is expected to continue moving along the coast and to eventually go out to the Wendell Sea, although it鈥檚 not known how long the process will take, Cloward said.
Karen Alley, an assistant professor with the University of Manitoba鈥檚 Department of Environment and Geography in Winnipeg, said the calving of a large iceberg doesn鈥檛 mean the ice shelf itself is in danger of collapsing.
鈥淭he Brunt Ice Shelf is not rapidly thinning due to ocean or atmospheric warming, and while it normally loses a lot of mass to calving, that mass is replaced by ice flow from the continent at about the same rate as it breaks off,鈥� Alley said by email on Thursday.
Glaciers and ice shelves that reach the ocean all calve periodically, but large calving events are rare and so it can be difficult to tell if they are a sign of change or normal behaviour, she said.
There aren鈥檛 any massive ice shelves in North America that are comparable to the Brunt Ice Shelf. However, many glaciers in Canada, Greenland and other parts of the Arctic do release smaller icebergs.
鈥淭hese icebergs can be a navigational hazard, so it's important to monitor their movements and understand the calving processes that create them in order to predict future iceberg changes in a warming Arctic,鈥� Alley said.
鈥淢any parts of Antarctica are melting and retreating rapidly, making the Antarctic Ice Sheet the largest concern for sea-level rise over the next few centuries,鈥� Alley said. 鈥淭he region where the Brunt Ice Shelf is located is a fairly stable part of Antarctica, making it likely that large calving events there are not of global concern.鈥�
