An extraordinary iceberg has passed, but not forgotten

You probably remember the A68a iceberg, which rose to fame a few minutes back in 2017 when it broke through an ice shelf on the Antarctic Peninsula. Hardly your everyday iceberg, it’s one of the largest ever seen, over 100 miles long and 30 miles wide.

The iceberg drifted slowly through the icy Weddell Sea for several years, before evaporating as it entered the Southern Ocean. The last time we heard about it, in 2020, it was brought down to the island of South Georgia in the South Atlantica little shriveled and battered after a journey of more than a thousand miles.

Alas, ol’ A68a is no more. Last year, about 100 miles from South Georgia, it finally did what all last icebergs do: thin to the point of breaking into tiny pieces and eventually drifting into nothingness.

In its infancy, A68a was nearly 800 feet thick, though all but its 120 feet were hidden below the waterline.

Ecologists and others have feared that during its journey the iceberg could become ground zero near South Georgia. That could prevent the millions of penguins and seals that live and breed there from accessing their feeding grounds in the ocean.

That didn’t happen. New research shows that A68a does more driving, and most likely only briefly over a feature on the seabed as it rotates and continues until it crashes.

But the study also revealed another potential iceberg threat to the ecosystems around South Georgia. As it passes through the relatively warm waters of the South Atlantic into the South Atlantic, it melts from below, eventually releasing large amounts of fresh water into the waters near the island. Excessive freshwater runoff can affect plankton and other organisms in the marine food chain.

The scientists, led by Anne Braakmann-Folgmann, a PhD student at the Center for Polar Observation and Modeling at the University of Leeds in the UK, used satellite imagery to track shape and position. of the iceberg during its journey. (Like other large Antarctic icebergs, it is named after the convention established by the US National Ice Center, which is a bit less flashy than the icebergs used for hurricanes.)

The image shows how the area of ​​the iceberg has changed over time. The researchers also determined its thickness using data from satellites that measure the height of the ice. By the time it disintegrated, the A68a was 200 feet thinner overall, Ms. Braakmann-Folgmann said.

The A68a leaves its mark. Researchers who have discovered published in the journal Environmental Remote Sensing, it is estimated that melting in the vicinity of South Georgia resulted in the release of about 150 billion tons of freshwater. That’s enough to fill an Olympic-sized swimming pool 61 million times, the researchers say, although since the ice is already floating its melting has not contributed to sea level rise.

Not only is the water clean and unsalted, but it also contains large amounts of iron and other nutrients. Ms. Braakmann-Folgmann is helping another group of researchers, from the British Antarctic Survey, who are trying to determine the ecological impacts of icebergs and meltwater.

As the iceberg neared South Georgia, the scientists participating in the survey were able to deploy an autonomous underwater glider to collect water samples. On the island, they used equipment to track several species of gentoo penguins and fur seals, to see if the presence of icebergs would affect their feeding behaviour.

Geraint Tarling, a biological oceanographer who participated in the survey, said preliminary findings from tracking data suggest that penguins and seals have not changed their feeding patterns, as they may have been caught by the iceberg. get in the way or affect the prey.

Dr Tarling said: “At least in the colonial areas that we have seen, the impact from the iceberg is not as devastating as we feared.

But there’s still a lot of data to analyze, Dr. Tarling suggested, especially for water samples. A large amount of freshwater on the surface could affect the growth of phytoplankton, at the end of the food shift, or it could alter the combinations of plant species, he said. available ephemeral, he said.

Complicating analysis is that 2020, as the iceberg nears South Georgia, is also a bad year for krill, the small crustacean that ranks only above phytoplankton in the food chain.

Dr Tarling said that although A68a did not become an earthquake, several other large icebergs have occurred in recent decades. Landing and dragging icebergs can wreak havoc on ecosystems on or near the seafloor, he said.

And climate change is likely to lead to more earthquake episodes. Warming is causing parts of the large Antarctic ice sheets to flow faster toward the ocean, leading to more icebergs then moving north.

Dr Tarling said: “What we’re looking at is that the movement of the icebergs can actually deepen these areas of the seafloor.

https://www.nytimes.com/2022/01/26/climate/iceberg-a68a-antarctica.html An extraordinary iceberg has passed, but not forgotten

Fry Electronics Team

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