The breakup of Iceberg A68-A, in December 2020, was observed in Meteosat and GOES imagery.
26 April 2021
02 February 2021
By Jochen Kerkmann (EUMETSAT) and Scott Bachmeier (CIMSS)
Iceberg A68-A, the planet's largest iceberg made headlines in July 2017 when the huge block of ice broke from the Larsen C Ice Shelf on the Antarctic Peninsula (see the case study Massive iceberg breaks off from Antarctica). In November 2020, the iceberg was back in the spotlight, as it is drifted toward South Georgia, a remote island in the southern Atlantic Ocean (see track of the iceberg (Credit: NASA Earth Observatory). The question was whether the large iceberg would get stuck (grounded) on the island’s submarine shelf, or if it would flow around the island.
The iceberg and South Georgia island are both visible in the GOES-16 Cloud Type RGB from 2 December (Figure 1). At that time the iceberg measured 135 kilometers long and 68 kilometers wide (see image with range overlaid) - comparable to the island’s length and width of 167 and 37 kilometers. On the image green colour denotes snow or ice (snow covered South Georgia, iceberg A68-A), red is thin, high-level cirrus clouds and the blue-cyan colour is low level water clouds.
The iceberg was also visible on Meteosat-11 images, though at a very high viewing angle, i.e. at low spatial resolution. Figure 2 shows a comparison of the GOES-16 Natural Color RGB product (snow and ice in cyan colour) with the same RGB product from Meteosat-11. The difference in resolution/viewing angle is striking/outstanding.
The GOES-16 Natural Colour RGB animation from 2 to 29 December at 15:00 UTC every day (Figure 3), shows the movement of the iceberg. Most of the days, the iceberg is visible, even underneath clouds.
In the beginning, the iceberg approached South Georgia, but when it encountered the more shallow continental shelf waters between 13 and 16 December when it was just 100 km away from the island, it began to move south-southeastward, shear apart and release three smaller orphan icebergs (in addition to widespread small ice floes, not visible in the images).
On 16 December, a large piece broke off on the northern side of the A68-A iceberg, forming iceberg A68-D (it is believed that part got stuck on the continental shelf), and on 23 December, when the iceberg encountered the strong Antarctic Circumpolar current, two large pieces broke off on the southern side (A68-E and A68-F), likely caused by the ocean current shear.
By 28 January 2021, the mother iceberg A68-A and the large orphan iceberg A68-E had gone in totally different directions: A68-A was positioned south of South Georgia, while A-68-E had curved around the island and was north of South Georgia (Figure 4).
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