There are some smaller parts of ice that have broken off around the A68A. The image is from NASA Worldview Snapshots.
The megaberg A68A melted over three months in 2020/2021, entering the seas around the sub-Antarctic island of South Georgia.
In July of last year, the A68A was snapped off of the ice shelf on the Antarctic Peninsula and began its journey across the Southern Ocean. When it formed, it was the sixth largest on record and one-quarter the size of Wales. The berg received a lot of attention as it was close to South Georgia, raising concerns that it could harm the island's delicate ecology.
Satellite data was used by researchers from the Centre for Polar Observation and Modelling to chart the A68A iceberg's area and thickness throughout its life cycle. The authors show that the berg melted enough to avoid damaging the sea floor around South Georgia. A side effect of the melting was the release of a huge amount of fresh water in close proximity to the island, which could have a profound impact on the island's marine habitat.
The first two years of A68A's life were spent in the cold waters of the Weddell Sea, where it experienced little in the way of melting. It traveled through warm waters after it began its journey across Drake Passage. As the berg moved in the Scotia Sea around South Georgia, it lost 67 meters from its initial 236-meter thickness.
Over time, the A68A iceberg was thin and broke. The melt rates go up when the ice is in the open ocean. Satellite altimetry data from ICESat-2 was used to derive the thickness. The shape and size were derived from satellite data. Anne Braakmann-Folgmann is a credit.
Laura Gerrish, a mapping specialist at BAS and co-author of the study said that A68 was an " absolutely fascinating iceberg to track all the way from its creation to its end." We were able to follow every move and break-up of the berg as it moved northward through the alley and into the Scotia Sea, where it gained speed and approached the island of South Georgia very closely.
If the sea floor is too deep, an ice cube can get stuck. The berg can block ocean currents and the scour marks can destroy fauna. When A68A approached South Georgia, all of these possibilities were feared. The study shows that it broke apart after colliding with the sea floor, making it less of a risk. By the time it reached the shallow waters around South Georgia, the iceberg's hull had shrunk to 141 meters below the ocean surface, shallow enough to avoid the deep sea.
The impact of the huge ice cube's visit will be felt by the wildlife around South Georgia. When the ice shelves are broken, the ocean currents and wind allow the glaciers to drift with the cold fresh meltwater and minerals as they melt. The local ocean circulation is influenced by this process. At its peak, the ice was melting at a rate of 7 meters per month, and in total, it released a staggering 152 billion tons of fresh water.
The animation shows the journey of the A68A ice shelf from the Antarctic Peninsula to the deep ocean of Scotia Sea and then to South Georgia at the end of its lifetime. Warming ocean conditions caused the berg to shrink. The ocean temperature is derived from the World Ocean Atlas and the elevation and ocean depth are based on data from GEBCO. The positions and lengths of the ice are taken from the database and the thickness is calculated from satellite data. Credit: Anne Braakmann.
The lead author of the study is Anne Braakmann-Folgmann, who is a researcher at the School of Earth and Environment. The next thing we want to learn is whether the amount of melt water had a positive or negative impact on the environment around South Georgia. Because A68A took a common route across the Drake Passage, we hope to learn more about how they influence the polar oceans.
Observations from five satellites have been used to chart the journey of A68A. The area change was recorded using a combination of imagery. The thickness change was measured using two satellites. The area, thickness, and volume change were determined by combining these measurements.
The island of South Georgia is approaching the A68A iceberg. There are clouds in the left hand image. The image is from NASA Worldview Snapshots.
The European Space Agency's ability to study every move of the iceberg is thanks to the use of a variety of measurement techniques. Data from altimetry missions add a third aspect to the picture, as they measure the height of the surfaces underneath the satellites, and can observe how an ice cap will melt.
A. Braakmann-Folgmann et al, observing the breakdown of the A68A iceberg from space, is available. The journal is titled "PukiWiki" and can be found at: www.PukiWiki.org
Satellites show a mega-iceberg releasing 152 billion tons of fresh water into the ocean.
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