Another iceberg calves in the Weddell Sea | Polarjournal
In the early hours of May 20, 2024, iceberg A-83 was the third iceberg to calve from the Brunt Ice Shelf in the last four years. (Photo: ESA)

A 380 km² iceberg broke off the Brunt Ice Shelf in the early hours of May 20, 2024. The event had been expected for several weeks because of cracks that had formed in the 150-metre-thick ice shelf.

The iceberg calved after a 14 km long fissure formed that is perpendicular to the existing Halloween crack. This was preceded by a long period of weakening of the ice at the McDonald Ice Rumples. The break-off is the third largest iceberg break-off in the last four years in the area where the British Halley Research Station is located. The new break-off occurred about a decade after scientists from the British Antarctic Survey (BAS) first discovered the growth of huge cracks in the ice.

The Sentinel-1 observation satellite is responsible for making radar-based observations of the Earth from its orbit at an altitude of around 700 km. It flies in an orbit close to the poles and scans the earth in strips. The width of the observed strips varies between 80 and 410 km. (Photo: ESA)

GPS monitoring of the iceberg

Dr. Oliver Marsh,a glaciologist who worked for the British Antarctic Survey (BAS) on the Brunt Ice Shelf for four seasons, discovered the calving for the first time using GPS devices: “These are single-frequency GPS devices, they’re not particularly accurate, but they tell you when something big is happening. We saw a movement of a few hundred meters within an hour, which is a good indication that the iceberg has broken off. Satellite images then confirm the GPS data.”

The separation of iceberg A-83 is the third significant calving of an iceberg from this region in the last four years. On February 26, 2021, an iceberg named A-74 formed on the Brunt Ice Shelf, followed by an even larger iceberg named A-81 on January 22, 2023. (Photo: ESA)

The Brunt Ice Shelf Location of the Halley Research Station

The Brunt Ice Shelf is also the location of the Halley Research Station of the British Antarctic Survey. This is where the hole in the ozone layer was discovered in 1985. Due to the risk of cracks, the Halley station was moved 23 kilometers in 2016 and is no longer manned in winter.

BAS glaciologists who have been monitoring the ice shelf’s behavior say that the speed of the ice shelf where the research station is located has stabilized since the last calving last year and do not expect any reaction to this new event.

In the past, the ice shelf flowed at a rate of 400-800 m (1,300-2,600 feet) per year. It now moves by around 1,300 m (4,300 feet) per year.

The Halley station consists of eight modules whose supports can be raised hydraulically to keep them above new ice and snow. In addition, the supports end in large skis so that the entire station can be moved to another location by tractors if necessary. (Photo: British Antarctic Survey)

Prof. Adrian Luckman, Professor at Swansea University: “Antarctica’s floating ice shelves grow gradually by ice flow and shrink episodically by iceberg calving. The balance between these two processes impacts their ability to hold back ice on land. It is concerning, therefore, that even in this relatively cold sector of Antarctica there have now been three large iceberg calvings in the last 3-4 years. The Brunt Ice Shelf is providing plenty of data to help us understand the calving process and predict the future evolution of these important ice bodies.”

Heiner Kubny, PolarJournal

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