“Megaiceberg” threw a huge volume of fresh water into the ocean

At its peak, the monster iceberg A68 was dumping more than 1.5 billion tons of fresh water into the ocean every day.

By comparison, this is about 150 times the volume of water consumed daily by all British residents.

For a brief period, the A68 was the largest iceberg in the world.

It was nearly 6,000 square kilometers (2,300 square miles) when it broke out of Antarctica in 2017. But by early 2021, it was gone.

One trillion tons of ice is gone.

Researchers are now trying to determine what impact A68 had on the environment.

A team led by experts at the University of Leeds analyzed all satellite data to calculate the giant’s changes in size as it moved north from the White Continent, across the Southern Ocean and into the South Atlantic.

This allowed the team to estimate the varying rate of melting over the three and a half years of the megaberg’s existence.

One key period was obviously at the end, when A68 was approaching the warmer climate of the British overseas territory of South Georgia.

For some time there had been fears that the giant clump might run aground in the surrounding shallow waters, blocking foraging routes for millions of penguins, seals and whales.

But that never happened because, as the crew can now show, the A68 lost enough keel depth to stay afloat.

“It appears that it briefly touched the continental shelf. At that point the berg made a turn, and we saw a small piece of it break off. But that wasn’t enough to ground the A68,” Dr. Anne Braakmann-Folgmann of Leeds told BBC News.

“And I think you can see the reason for that in the thickness estimates,” added study co-author Professor Andrew Shepherd. “By that time the berg keel was averaging 141 m, and the bathymetric charts (depths) in the area showed 150 m. In the end, it was very challenging.”

By April 2021, A68 had disintegrated into countless small fragments that could not be traced. But its impact on the ecosystem would be much more long-term.

It is now recognized that giant tabular, or flat-topped, bergs have a significant impact wherever they are located.

Their influx of freshwater will alter local currents. And the iron, other minerals, and even organic matter they collect during their lives and then dump into the ocean will contribute to biological production.

The British Antarctic Survey has been able to place several robotic gliders in the A68 area to monitor conditions before the ice mass disappears completely.

The data from these and other instruments, while not yet fully analyzed, have revealed some interesting features, said biological oceanographer Professor Geraint Tarling.

“We think there’s a really strong signal in the change in phytoplankton flora around A68, as well as in the actual deposition of material into the deeper parts of the ocean. The particle sensor on the glider was picking up very strong signals of deposition coming from the berg,” he told BBC News.

For more information on A68’s changing shape and freshwater fluxes, see an article published in the journal Remote Sensing of Environment.

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