Sciency Thoughts: Brunt Ice Shelf

Showing posts with label Brunt Ice Shelf. Show all posts

Sunday, 28 February 2021

Large iceberg calves from the Brunt Ice Shelf, Antarctica.

A huge iceberg (1270 km² or the size of the county of Bedfordshire) has broken off the 150m thick Brunt Ice Shelf, according to a press release issued by the British Antarctic Survey on 26 February 2021, almost a decade after scientists first detected growth of vast cracks in the ice.

The Brunt Ice Shelf is the location of British Antarctic Survey’s Halley Research Station. British Antarctic Survey glaciologists, who have been expecting a big calving event for at least a decade, say that the research station is unlikely to be affected by the current calving. The 12 person team working at the station left mid-February by British Antarctic Survey Twin Otter aircraft. The station is now closed for the Antarctic winter.

North Rift crack photographed by Halley team in January 2021. British Antarctic Survey,

The first indication that a calving event was imminent came in November 2020 when a new chasm, called North Rift, headed towards another large chasm near the Stancomb-Wills Glacier Tongue 35 km away. North Rift is the third major crack through the ice shelf to become active in the last decade.

During January, this rift pushed northeast at up to 1 km per day, cutting through the 150 m thick floating ice shelf. The iceberg was formed when the crack widened several hundred metres in a few hours on the morning of 26 February, releasing it from the rest of floating ice shelf.

Map of Brunt ice shelf and Halley Research Station. British Antarctic Survey.

The glaciological structure of this vast floating ice shelf is complex, and the impact of ‘calving’ events is unpredictable. In 2016, the British Antarctic Survey took the precaution of relocating Halley Research Station 32 km inland to avoid the paths of ‘Chasm 1’ and ‘Halloween Crack’.

Since 2017, staff have been deployed to the station only during the Antarctic summer, because during the dark winter months evacuation would be difficult. ‘Chasm 1’ and ‘Halloween Crack’ have not grown in the last 18 months.

Jane Francis, Director of the British Antarctic Survey said 'Our teams at the British Antarctic Survey have been prepared for the calving of an iceberg from Brunt Ice Shelf for years. We monitor the ice shelf daily using an automated network of high-precision GPS instruments that surround the station, these measure how the ice shelf is deforming and moving. We also use satellite images from European Space Agency, NASA and the German satellite TerraSAR-X. All the data are sent back to Cambridge for analysis, so we know what’s happening even in the Antarctic winter, when there are no staff on the station, it’s pitch black, and the temperature falls below minus 50 °C. Over coming weeks or months, the iceberg may move away; or it could run aground and remain close to Brunt Ice Shelf. Halley Station is located inland of all the active chasms, on the part of the ice shelf that remains connected to the continent. Our network of GPS instruments will give us early warning if the calving of this iceberg causes changes in the ice around our station.'

Simon Garrod, Director of Operations at the British Antarctic Survey added 'This is a dynamic situation. Four years ago we moved Halley Research Station inland to ensure that it would not be carried away when an iceberg eventually formed. That was a wise decision. Our job now is to keep a close eye on the situation and assess any potential impact of the present calving on the remaining ice shelf. We continuously review our contingency plans to ensure the safety of our staff, protect our research station, and maintain the delivery of the science we undertake at Halley.'

Halley VI Research Station is an internationally important platform for, atmospheric and space weather observation in a climate-sensitive zone. In 2013, the station attained the World Meteorological Organization Global Atmosphere Watch Global station status, becoming the 29th in the world and 3rd in Antarctica.

Halley VI Research Station sits on Antarctica’s Brunt Ice Shelf, which is up to 150 m thick. This floating ice shelf flows at a rate of up to 2 km per year west towards the sea where, at irregular intervals, it calves off as icebergs.

Long-term monitoring of the natural changes that occur in the ice shelf has revealed changes, including growth of a recently-formed chasm, the North Rift. Halley VI Research Station has been unoccupied during the last four winters because of the complex and unpredictable glaciological situation.

Change in the ice at Halley is a natural process and there is no connection to the calving events seen on Larsen C Ice Shelf, and no evidence that climate change has played a significant role.

During the 2016-17 Antarctic Summer season (Nov-March), in anticipation of calving, the eight station modules were uncoupled and transported by tractor to a safer location upstream of Chasm-1.

Over the summer 18/19, the British Antarctic Survey installed an autonomous power generation and management system, Halley Automation project, which provides a suite of scientific instruments with power even when we have no staff at the station. This system has proved effective in running through more than eight months of darkness, extreme cold, high winds and blowing snow and delivering important data back to UK.

There have been six Halley research stations on the Brunt Ice Shelf since 1956.

Sunday, 14 February 2021

New crack spotted on the Brunt Ice Shelf, Antarctica.

In early 2019, all eyes were fixed on the Brunt Ice Shelf in Antarctica, where a massive iceberg, around the size of Greater London, appeared poised to break off. Almost two years later, the berg is desperately clinging on, although current data indicate calving is imminent. A new crack, spotted in images captured by the Copernicus Sentinel missions, now suggests the potential for calving of multiple bergs, according to a press release from the European Space Agency on 12 February 2021.

For years, glaciologists have been tracking a number of cracks in the Brunt Ice Shelf, which borders the Coats Land coast in the Weddell Sea sector of Antarctica. The lengthening of two main cracks in the ice shelf, separated only by a few kilometres, have been closely monitored by satellite imagery. Chasm 1, the large crack running northwards from the southernmost part of Brunt, has been set in place for more than 25 years, while the Halloween crack was first spotted on 31 October 2016.

A more recent, unnamed crack was first noticed in observations from the Copernicus Sentinel-1 mission in late-2019, recently extending by more than 20 km in length. Satellite data has also been used to track the movement and measure the resulting strain in the ice shelf. The map below shows the ice surface velocity on the Brunt and Stancomb-Wills Ice Shelf complex, derived by comparing two Sentinel-1 acquisitions captured on 5 January and 17 January 2021.

Ice velocity map of the Brunt and Stancomb-Wills Ice Shelf. European Space Agency.

The data indicate the region of the floating ice shelf, to the north of the new crack, to be the most unstable, with an approximate movement of almost 5 m per day. The central portion has an average velocity ranging from 2 to 2.5 m per day, while the lower area (visible in blue) suggests a more stable zone of the ice shelf.

'Though appearing poised to calve in 2019, the south westernmost region of the Brunt Ice Shelf tenaciously resisted separation,' noted European Space Agency’s Mark Drinkwater. 'Since then, Sentinel-1 data indicate the nose of the ice shelf to be pivoting clockwise around the McDonald Ice Rumples region in which point the shelf ice is grounded on shallow underwater topography.'

'Meanwhile, the strong gradient in ice velocity towards the faster moving Stancomb-Wills ice stream, and ice shelf in the north, has activated a new rift which now threatens the release of a second large iceberg.'

New crack in the Brunt Ice Shelf. European Space Agency.

Routine monitoring from satellites offer unprecedented views of events happening in remote regions, and show how ice shelves are responding to changes in ice dynamics, air and ocean temperatures. During the dark winter months in Antarctica, radar images are indispensable because, apart from the region being remote, radar continues to deliver images regardless of the dark weather.

Mark Drinkwater continued, 'With today’s Copernicus monitoring system, we are far better equipped not only to observe events in remote places like Antarctica in near real time, but more importantly, to turn this scientific data into theoretical understanding of complex ice fracture processes.'

History shows that the last major event took on the Brunt Ice Shelf took place in 1971, when a portion of ice calved north of the area known as the McDonald Ice Rumples in what appears to be replicated by today’s Halloween Crack.

With the ice shelf deemed unsafe due to the encroaching cracks in 2017, the British Antarctic Survey closed up their Halley VI Research Station, and re-positioned south of Halloween Crack to a more secure location. Operational since 2012, Halley VI is made up of eight interlinked pods built on skis. This allows the pods to be easily moved in case of unstable ice and cracks on the ice shelf.