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Iceberg A23a’s Epic Journey from Antarctica to the Open Ocean

The monumental voyage of Iceberg A23a, an ice mass larger than New York City, from Antarctica to the open ocean is altering the marine environment. This significant journey, closely monitored by scientists, is a unique opportunity to study our planet’s dynamic polar regions.

By Beth Snider · December 8, 2023

Iceberg A23a

In the icy wilderness of Antarctica, a colossal iceberg, known as A23a, has embarked on a remarkable journey. This icy behemoth, three times the size of New York City, has broken free from its grounded state and is now adrift in the open ocean.

Antarctica, the world’s fifth-largest continent, is a frozen landscape blanketed by a thick layer of ice and snow. As snow accumulates in the heart of Antarctica, it forms a layer of ice. Over time, this ice transforms into slow-moving rivers of ice, known as glaciers, which inch their way towards the sea. These glacial masses extend beyond the land’s edge, forming massive “ice shelves” that float on the water below. Occasionally, the edges of these ice shelves fracture and break off, a natural process known as “calving”. In 1987, a gargantuan iceberg, A23, calved from Antarctica’s Filchner Ice Shelf, carrying with it Druzhnaya Station, a Soviet Union research station.

A23 subsequently fragmented into three smaller pieces, one of which was A23a. Despite being smaller than its parent, A23a is still an awe-inspiring sight. Measuring about 46 miles long and 37 miles wide, it’s larger than the US state of Rhode Island. Scientists estimate that the iceberg is approximately 1,200 feet thick, just shy of the height of New York City’s Empire State Building.

A23a Now on the Move  Nasa Earth Observatory / Antarctic Iceberg Sails Away

For over 30 years, A23a remained grounded to the sea bottom due to its immense height. However, in 2020, it began to move again, scraping its way across the sea floor. By November 2023, it had navigated past the northern edge of Antarctica and ventured into open water. The future of the iceberg remains uncertain, it could become grounded again, or it may continue its northward journey. As it drifts away from Antarctica, the icy mass will encounter warmer weather, leaving behind a trail of cold, fresh water and minerals as it melts. This will alter the temperature and salinity of the surrounding seawater, impacting the local marine life.

View of A23a from the deck of RRS Sir David Attenborough  British Antartic Survey Website / Rich Turner
It is incredibly lucky that the iceberg’s route out of the Weddell Sea sat directly across our planned path, and that we had the right team aboard to take advantage of this opportunity. We’re fortunate that navigating A23a hasn’t had an impact on the tight timings for our science mission, and it is amazing to see this huge berg in person – it stretches as far as the eye can see.
Dr Andrew Meijers, Chief Scientist aboard the RRS Sir David Attenborough and Polar Oceans Science Leader at British Antarctic Survey (BAS)

The British Antarctic Survey (BAS) recently dispatched a research vessel to study A23a as it traversed the Weddell Sea. The scientists onboard were able to capture images and videos of the iceberg and collect samples of the surrounding seawater.

Calving of icebergs from Antarctica’s ice shelves is part of the natural life cycle of glaciers. Polar ecosystems play a crucial role in regulating the balance of carbon and nutrients in the world’s oceans and are impacted by melting icebergs in numerous ways.
Professor Geraint Tarling, Principal Investigator on the BIOPOLE Programme and Ecosystems Science Leader at BAS

The RRS Sir David Attenborough encountered the iceberg during its journey to the Weddell Sea, part of its planned route for the inaugural 10-day BIOPOLE cruise. This groundbreaking scientific mission, the first aboard the new research ship, explores how Antarctic ecosystems and sea ice influence global ocean cycles of carbon and nutrients. The results will enhance our understanding of climate change’s impact on the Southern Ocean, including its effects on marine plants, copepods, penguins, and whales, and their roles in climate regulation and ocean health.