Mega Iceberg – One of the Largest on Record – Released 150 Billion Tons of Freshwater Near Island

A-68A’s place on December 17, 2020. Credit score: British Antarctic Survey/ESA

In July 2017, an enormous iceberg, named A-68, snapped off Antarctica’s Larsen-C ice shelf and commenced an epic journey throughout the Southern Ocean. Three and a half years later, the primary a part of iceberg, A-68A, drifted worryingly near South Georgia. Considerations have been that the berg would run aground within the shallow waters offshore. This might not solely trigger harm to the seafloor ecosystem but in addition make it tough for island wildlife, equivalent to penguins, to make their technique to the ocean to feed. Utilizing measurements from satellites, scientists have charted how A-68A shrunk in direction of the tip of its voyage, which fortuitously prevented it from getting caught. Nevertheless, the draw back is that it launched a colossal 152 billion tonnes of freshwater near the island, doubtlessly having a profound impact on the island’s marine life.

When A-68 was spawned, it had a floor space of greater than twice the scale of Luxemburg – one of many largest icebergs on report.

It misplaced a bit of ice virtually instantly after being calved, ensuing within the bigger berg being renamed A-68A, and its offspring turned A-68B. In April 2020, A-68A misplaced one other chunk subsequently known as A-68C.

Antarctic icebergs are named from the Antarctic quadrant wherein they have been initially sighted, then a sequential quantity, after which if the iceberg breaks, a sequential letter is added.

The map exhibits the totally different positions of the berg over the course of its three-year journey. The map additionally contains historic iceberg tracks, primarily based on knowledge from various satellites together with ESA’s ERS-1 and ERS-2 as a part of the Antarctic Iceberg Monitoring Database. Credit score: Comprises modified Copernicus Sentinel knowledge (2021), processed by ESA; Antarctic Iceberg Monitoring Database

For the primary two years of its life, A-68A stayed within the chilly waters of the Weddell Sea near its guardian ice shelf. Right here, it skilled little in the way in which of melting.  Nevertheless, as soon as the berg started its northward journey throughout the Drake Passage, it traveled via more and more heat waters and commenced to soften.

Altogether, the A-68A iceberg thinned by 67 meters from its preliminary thickness of 235 meters, with the speed of melting rising sharply because the berg drifted within the Scotia Sea round South Georgia.

A paper revealed in Distant Sensing of Surroundings describes how researchers from the Centre for Polar Remark and Modelling within the UK and the British Antarctic Survey mixed measurements from totally different satellites to chart how A-68A modified in space and thickness all through its life cycle.

The journey of A-68A was charted utilizing observations from 5 totally different satellite tv for pc missions.

To trace how the realm of A-68A modified, they used optical imagery from the Copernicus Sentinel-3 mission and from the MODIS instrument on the US Terra mission, together with radar knowledge from the Copernicus Sentinel-1 mission. Whereas the Sentinel-1 radar imagery affords all-weather functionality and better spatial decision, MODIS and Sentinel-3 optical imagery have greater temporal decision however can't be used in the course of the polar evening and on cloudy days.

To measure modifications within the iceberg’s freeboard, or the peak of the ice above the ocean floor, they used knowledge from ESA’s CryoSat mission and from the US ICESat-2 mission. Understanding the freeboard of the ice signifies that the thickness of your complete iceberg could be calculated.

All these measurements collectively allowed the scientists to calculated how the iceberg’s quantity modified and due to this fact how a lot freshwater it launched.

Tommaso Parrinello, ESA’s CryoSat Mission Supervisor, mentioned, “Our capacity to review each transfer of the iceberg in such element is because of advances in satellite tv for pc methods and the usage of a wide range of measurements. Imaging satellites report the form of the iceberg and knowledge from altimetry missions like CryoSat add one other necessary dimension as they measure the peak of surfaces – which is important for calculating modifications in quantity.”

Visualizing the quantity of freshwater launched from A-68A. Credit score: CPOM/ESA/Google basemap

The brand new research reveals that A-68A collided solely briefly with the ocean ground and broke aside shortly afterward, making it much less of a danger when it comes to blockage. By the point it reached the shallow waters round South Georgia, the iceberg’s keel had lowered to 141 meters beneath the ocean floor, shallow sufficient to only keep away from the seabed which is round 150 meters deep.

If an iceberg’s keel is just too deep it could get caught on the ocean ground. This may be disruptive in some ways; the scour marks can destroy fauna, and the berg itself can block ocean currents and predator foraging routes.

Nevertheless, a aspect impact of the melting was the discharge of a colossal 152 billion tonnes of freshwater near the island – a disturbance that might have a profound impression on the island’s marine habitat.

When icebergs detach from ice cabinets, they drift with the ocean currents and wind, releasing chilly contemporary meltwater and vitamins as they soften. This course of influences the native ocean circulation and fosters organic manufacturing across the iceberg.

Anne Braakmann-Folgmann, PhD candidate on the Centre for Polar Remark and Modelling and lead writer of the research mentioned, “It is a big quantity of meltwater, and the following factor we wish to be taught is whether or not it had a constructive or unfavorable impression on the ecosystem round South Georgia.

“As a result of A-68A took a typical route throughout the Drake Passage, we hope to be taught extra about icebergs taking an analogous trajectory, and the way they affect the polar oceans.”

For extra on this research, see Huge Iceberg Launched Over 150 Billion Tons of Contemporary Water Into Ocean As It Scraped Previous South Georgia.

Reference: “Observing the disintegration of the A68A iceberg from area” by A. Braakmann-Folgmann, A. Shepherd, L. Gerrish, J. Izzard and A. Ridout, 10 January 2022, Distant Sensing of Surroundings.
DOI: 10.1016/j.rse.2021.112855