Once considered stable, The Brunt Ice Shelf is accelerating rapidly into the Weddell Sea, according to the British Antarctic Survey (BAS), which monitors Brunt at its Halley Research station. Halley Station recorded the retreat after two massive icebergs calved.
The surge of glacial ice occurred shortly after Iceberg A81 when it snapped off the 500-foot thick ice shelf. The floating shelf has moved from half a mile in January to almost one mile today. The abstract notes, "Initially, the rate of acceleration increased by a factor of ten, with a second, smaller calving at the end of June 2023 leading to further tripling of acceleration. The acceleration is caused by reduced buttressing at the McDonald Ice Rumples due to losing contact with the sea floor. It has led to high strain rates to the south, with potential consequences for the stability of the remaining ice shelf." The shelf has given researchers no reason to believe that the remaining shelf will disintegrate anytime soon. They believe the glacier will be grounded again at some point. Where that would be was not identified; it could be another ridge at the McDonald Ice Rumples. The BAS monitors the glacier daily.
NASA 2021 Image of the cracks, Chasm 1, New, Halloween, and the McDonald Ice Rumples for reference.
Icebergs are named after the quadrant where they are first sighted.
Iceberg names are derived from the Antarctic quadrant in which they were originally sighted. The quadrants are divided counter-clockwise in the following manner:
A = 0-90W (Bellingshausen/Weddell Sea)
B = 90W-180 (Amundsen/Eastern Ross Sea)
C = 180-90E (Western Ross Sea/Wilkesland)
D = 90E-0 (Amery/Eastern Weddell Sea)
A81 was hanging on by a thread in this image. A81 detached completely in January of 2023.
From the BBC:
The data comes from precise GPS measurements around Halley and radar observations by the European Union's Sentinel-1a satellite.
The acceleration follows the calving of two major icebergs from the leading edge of the Brunt - a 1,300-sq-km (500-sq-mile) behemoth called A74, in February 2021, and an equally mammoth slab called A81, in January this year.
A74's impact was minimal but A81 appears to have released the shelf from a shallow section of seafloor that normally pins it in place and slows the seaward momentum.
What is more, these calvings - and there was another smaller one in June - have prompted new areas of stress in the ice shelf.
13 September 2023 Press releases
ANTARCTICA – Following the calving of the A-81 iceberg at the end of January 2023, the Brunt Ice Shelf is moving faster than before. It is currently moving approximately 4 metres a day towards the sea, whereas before the calving it moved at an average of between 1-2.5 metres a day. The observations have been submitted this week to the journal The Cryosphere.
The Brunt Ice Shelf is one of the most studied ice shelves in the world. Its glaciological structure is complex, and the impact of calving events is often unpredictable. Researchers consider that climate change has not played a significant role in the recent acceleration of the Brunt Ice Shelf. It has accelerated due to the loss of its connection with the seafloor in an area known as the McDonald Ice Rumples, following the calving of the A-81 iceberg. This connection helped stabilise the ice shelf for most of the last 67 years since it was first occupied and instrumented. The ice shelf is now moving at a rate usually only measured on ice shelves fed by exceptionally fast flowing outlet glaciers such as Thwaites Glacier in West Antarctica.
There appears to be no mention of the Weddell Sea's warming bottom water nor the shattered record low in sea ice this winter in the Southern Ocean. There is also no mention of the heat and thinning of cold water's role in the Brunt Ice shelf losing contact with the shallow sea pinning point it was lodged on.
CNN on the Weddell Sea deep ocean water:
Deep ocean water in the Antarctic is heating up and shrinking, with potentially far-reaching consequences for climate change and deep ocean ecosystems, according to a report.
“Antarctic bottom water” is the coldest, saltiest water on the planet. These waters play a crucial role in the ocean’s ability to act as a buffer against climate change by absorbing excess heat and human-caused carbon pollution. They also circulate nutrients across the ocean.
But in the Weddell Sea, located east of the Antarctic Peninsula, this vital water mass is in decline, due to long-term changes in winds and sea ice, according to the study published Monday by the British Antarctic Survey.
SNIP
They found that the volume of the cold bottom waters has shrunk by more than 20% over the past three decades. They also found that ocean waters deeper than 2,000 meters (6,600 feet) have warmed four times faster than the rest of the global ocean.
“We used to think that changes in the deep ocean could only occur over centuries. But these key observations from the Weddell Sea show that changes in the dark abyss can take place over just a few decades,” Alessandro Silvano from the University of Southampton in the UK, a co-author of the study, said in a statement.
