A gigantic iceberg the size of urban Sydney has broken off an ice shelf in Antarctica, the Australian Antarctic Division (AAD) says.
Key points:
* The iceberg, named D28, broke off the Amery ice shelf on September 26
* The last major calving on the shelf was in the 1960s
* Scientists do not believe the event is linked to climate change and say major calving events happen every 60 to 70 years
The 1,636-square-kilometre iceberg — named D28 — was calved from the Amery ice shelf in east Antarctica.
AAD glaciologist Ben Galton-Fenzi said the iceberg separated from the shelf last Thursday, and was noticed by scientists using satellite imagery.
Scientists had been monitoring a section of the ice shelf known as the Loose Tooth, which is next to where D28 broke off and is so named because it looks precariously attached.
"The calving will not directly affect sea level, because the ice shelf was already floating, much like an ice cube in a glass of water," Dr Galton-Fenzi said.
"But what will be interesting to see is how the loss of this ice will influence the ocean melting under the remaining ice shelf and the speed at which the ice flows off the continent."
Last major iceberg broke off Amery in 1960s
The 60,000-square-kilometre Amery ice shelf is the third largest shelf in Antarctica and is situated between Australia's Davis and Mawson research stations.
Photo: A crack in the Amery ice shelf, pictured in 2003. (Supplied: Australian Antarctic Division )
An ice shelf is a section of ice that juts out into the sea.
Snow from the interior builds up and flows out to the edge of the continent. At the edges it thins, and because ice is less dense than water, it sits on top of the ocean instead of on the seabed.
Scientists have been studying the Amery shelf since the 1960s, and recorded the last major calving event in late 1963 or early 1964.
The massive tabular iceberg was about 10,000 square kilometres, and split into two smaller bergs a year later.
Infographic: The anatomy of an ice shelf. (Supplied: Dr Sue Cook)
Calving 'not linked to climate change'
Helen Amanda Fricker, from the Scripps Institution of Oceanography in the US, said scientists first noticed a rift in the ice shelf nearly 20 years ago.
"We … predicted a large iceberg would break off between 2010-2015," Professor Fricker said.
"I am excited to see this calving event after all these years. We knew it would happen eventually, but just to keep us all on our toes, it is not exactly where we expected it to be.
Mark Doman @MarkDoman
The D28 iceberg that broke away from the Amery ice shelf in Antarctica last week. Read more about it here: https://ab.co/2o42umU Imagery via @CopernicusEU and @sentinel_hub
"We don't think this event is linked to climate change; it's part of the ice shelf's normal cycle, where we see major calving events every 60-70 years."
But Sue Cook from the Institute of Marine and Antarctic Studies (IMAS) believes climate change will have an impact on ice shelves in the future.
"We definitely expect iceberg calving to increase in the future under climate change," she said.
"There are a number of different processes that'll happen. As waters around Antarctica warm up, they'll start thinning the ice shelves and making them more vulnerable to breaking up.
"Also you get increased surface melt on the ice shelves and that can get into fractures and forces them to expand."
She said the iceberg would be tracked.
"I wouldn't expect it to produce a big risk to shipping at the moment," she said.
"It's so large it should be easy to track and easy to plan where the iceberg is going to move."
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