Antarctica iceberg A23a: The place is it now and does it pose any risk?

The largest iceberg in the world is on the move after being stuck in the Antarctic seafloor for nearly 40 years. Known as A23a, the iceberg has now floated beyond the northernmost point of Antarctica and is on its way to melt in warmer waters.

Where is the iceberg now?

It is just north of the tip of the Antarctic Peninsula, which extends from West Antarctica towards South America. Satellite imagery provided by the British Antarctic Survey shows the iceberg wending its way through the Weddell Sea in the Southern Ocean throughout 2022 and 2023, pushed by currents and winds across thousands of kilometres. The mass of ice reached just beyond the Antarctic Peninsula in late November.

Most icebergs from the Weddell Sea end up carried by currents into the South Atlantic’s “iceberg alley” where they eventually melt.

When did it start moving?

The iceberg first calved off the Filchner-Ronne ice shelf in West Antarctica in 1986, but it immediately ran aground on the ocean floor, remaining in place for more than 30 years. Then in 2020 Andrew Fleming at the British Antarctic Survey noticed it was beginning to move, he told the BBC.

“Eventually it was going to decrease [in size] sufficiently to lose grip and start moving,” he told the outlet.

How big is the iceberg?

It covers nearly 4000 square kilometres, an area more than four times as big as New York City. It is around 400 metres thick.

While this makes it the largest iceberg now bobbing in the world’s oceans, it is not the largest on record. That behemoth, known as A-76, measured 4320 square kilometres when it broke off from West Antarctica in 2021.

How rare are giant icebergs like this one?

Chad Greene at NASA’s Jet Propulsion Laboratory in California says a large iceberg like A23a calves off of one of Antartica’s ice shelves about once a decade; the Filchner Ice Shelf sees such an event about once every 50 years. “Icebergs are like earthquakes – we get lots of tiny ones, and a few really big ones like A-23.”

He says it is not uncommon for these giant icebergs to get stuck in place and stay that way, kept from melting much in the near-freezing Antarctic waters. “Icebergs this big can hang around for decades in one place, then one day decide to go for a jolly,” says Greene. “That’s when things get interesting.”

Does the iceberg pose any threat?

The iceberg does not pose a threat to people, although it may become a problem for wildlife, such as penguins or seals, if it runs aground in their feeding or breeding grounds in the Southern Ocean.

Is the movement of the iceberg linked to climate change?

Fleming told the BBC that researchers do not think there is a clear link between the iceberg’s recent movement and warmer waters driven by climate change. Greene agrees that its behaviour resembles a normal iceberg lifecycle.

However, Greene says it is clear that icebergs are breaking off Antarctica at a faster rate than snow is adding mass to the ice, “meaning climate change is causing the Antarctic Ice Sheet to lose mass at a significant rate”.

Researchers have been shocked by recent climate extremes in Antarctica, including record-high temperatures and vast areas of missing sea ice, which serve to buffer the continent’s ice shelves from warmer water and waves.

After reaching a record low in 2022, sea ice around the continent did not recover as much as usual this year, remaining far below average into the southern winter. In September, Antarctic sea ice set a new record when it reached a maximum extent that was more than a million square kilometres below the previous record low set in 1986.