Iceberg A23a is dead after a 40-year journey

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Abstract: Iceberg A23a was a tabular iceberg calved from East Antarctica's Filchner–Ronne Ice Shelf in 1986. Its area was approximately 1,505 sq. mi, which made it the largest iceberg in the world at the time. After a 40-year odyssey at sea, the megaberg submerged in the South Atlantic Ocean.

The 40-year-long journey of the Antarctic Iceberg A-23A, originally calved from the Filchner-Ronne Ice Shelf, comes to an end in fragmentation in the South Atlantic Ocean. The image captured by the VIIRS (Visible Infrared Imaging Radiometer Suite) on the NOAA-21 satellite on April 3, 2026, shows the remains of the iceberg at the end of its journey. The ice had drifted into the South Atlantic between the eastern tip of South America and the island of South Georgia, more than 2,300 kilometres north of where the iceberg first calved (NASA Earth Observatory, 2026).

Source: NASA

About Iceberg A23a

Iceberg A23a was nearly a trillion tonnes of tabular iceberg calved from East Antarctica's Filchner–Ronne Ice Shelf in 1986. Its area was approximately 1,505 sq. mi (3,900 sq. km), which made it the largest iceberg in the world at the time (Cooperative Institute for Research in the Atmosphere, n.d). It had shrunk to just over 170 square kilometres (66 square miles) by March 27, 2026 (NASA Earth Observatory, 2026). There are several larger icebergs floating in the Southern Ocean, but what made Iceberg A23a apart was its remarkable longevity post-calving off from the ice shelf.

The sojourn

Source: NASA

Iceberg A23a's historic journey was marked by landmark scientific events. The iceberg spent its early days in the Weddell Sea in the Southern Ocean, where it got stuck on the seabed for over 30 years due to its immense size and weight. In 2020, the iceberg again started its journey guided by ocean currents and the shape of the seafloor, and moved past the northern tip of the Antarctic Peninsula in November 2023. Later, it was trapped in a Taylor Column, a rotating column of fluid that forms above submerged objects in a rotating flow (Sharp, N., 2024), in the north of the South Orkney Islands, which kept A23a spinning in one spot and delayed its movement. In December 2024, A23a freed itself from the column and drifted further north through the Southern Ocean. Its area was merely 1,182 square kilometres in early January 2026, following the breakup of large pieces as it moved into relatively warm summer conditions by December 2025. The image captured by MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite showed the blue colouration on its surface on December 26, 2025,  indicating the presence of meltwater. And, finally, A23a drifted into the South Atlantic, but it has already made history.

Do You  Know?

Iceberg: An iceberg is ice that broke off from glaciers or ice shelves and is floating in open water. As per NOAA, to be classified as an iceberg, the height of the ice must be greater than 16 feet above sea level, the thickness must be 98-164 feet, and the ice must cover an area of at least 5,382 square feet.

Colours of Icebergs: Interestingly, icebergs come in various colours, which tell us about their structure or sources. A white iceberg is an indicator of lots of bubbles inside, whereas blue icebergs are very dense. Greenish-black icebergs may have calved off the bottom of a glacier, and darkly-striped icebergs carry moraine debris from the glacier (NASA Earthdata, n.d.).

Tabular Iceberg: These icebergs have steep sides and a flat top.

Calving: In the glaciological term, calving is the breaking off of ice from a glacier margin.

Way Forward

Scientists and researchers, using satellites and through direct observations while passing through A23a, have collected a lot of images and data on the 40-year-long journey of the iceberg. These images and data will answer questions about the factors driving iceberg motion, from ocean currents to the shape of the seafloor. All icebergs eventually meet the same fate—melting or disintegrating into smaller fragments. A23a is no exception. Some examples include Iceberg A-68, which calved from the Larsen C Ice Shelf in 2017 and disintegrated in January 2021 after drifting more than 2,500 km, and Iceberg B-15, which calved from Antarctica's Ross Ice Shelf in March 2000 and later fragmented into many smaller icebergs (NASA Earth Observatory, 2011, December 7). Scientists follow such icebergs' long journey with great interest to find clues about how Antarctica might respond to rising temperatures and subsequent climate changes.  Also, such giant icebergs release nutrients into the surrounding waters as they drift, stimulating phytoplankton growth. Phytoplankton is the foundation of marine food webs, which support marine life like penguins, whales, and other organisms.  Studying them could help researchers better understand the thriving ecosystems that develop along their paths (British Antarctic Survey, 2026).

References

●        NASA Earth Observatory. (2026, April 13). Megaberg ends its long odyssey at sea. NASA Earth Observatory, https://science.nasa.gov/earth/earth-observatory/megaberg-ends-its-long-odyssey-at-sea/?utm_source=chatgpt.com.

●        Cooperative Institute for Research in the Atmosphere. (n.d.). Iceberg A23A. Colorado State University. Iceberg A23A, http://satlib.cira.colostate.edu/event/iceberg-a23a/?utm_source=chatgpt.com.  

●        NASA Earth Observatory. (2026, April 13). Megaberg ends its long odyssey at sea. NASA Earth Observatory, https://science.nasa.gov/earth/earth-observatory/megaberg-ends-its-long-odyssey-at-sea/

●        Sharp, N. (2024, August). Trapped in a Taylor column. FYFD (Fluid Dynamics), https://fyfluiddynamics.com/2024/08/trapped-in-a-taylor-column/.

●        NASA Earthdata. (n.d.). Glacier power: What is glacial calving?, https://www.earthdata.nasa.gov/topics/cryosphere/glaciers/glacier-power/what-is-glacial-calving?utm_source=chatgpt.com

●        NASA Earth Observatory. (2011, December 7). Iceberg B-15J. NASA. https://science.nasa.gov/earth/earth-observatory/iceberg-b-15j-76599/

●        British Antarctic Survey. (2026, April 20). Not all icebergs are equal – and that matters for the climate, new study finds, https://www.bas.ac.uk/news/not-all-icebergs-are-equal-and-that-matters-for-the-climate-new-study-finds/

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