Interesting Events Here we describe recent, rapid changes in the cryosphere that are newsworthy. They may or may not be significant in a climate context.

Jeff Key, 27 May 2021

In early May 2021, the Ronne Ice Shelf in West Antarctica¹ produced one of the largest icebergs to break off from Antarctica in the recent past. The iceberg was named A-76 by the US National Ice Center (NIC)². When it broke from the ice shelf, its location was 75°17' South, 58°54' West (or -75.2833, -58.90), shown in Figure 1. This finger-shaped block of ice is around 170 km (105 mi) long and around 25 km (15 mi) wide. It has an area of 4,320 km² (1,668 mi²). It is considerably larger than the US state of Rhode Island (3144 km² or 1214 mi²), and larger than the Spanish island of Majorca (3650 km² or 1410 mi²). It is currently the largest iceberg in the world.

Figure 1: Map of Antarctica with the star indicating the approximate location of A-76 in early May 2021.

Figure 2 is a false-color, thermal infrared image of A-76 from the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument of the US Joint Polar Satellite System on 16 May 2021. Figure 3 is a synthetic aperture radar (SAR) from the European Space Angency's (ESA) Sentinel-1A satellite on 13 May 2021 (opposite orientation).

Figure 2: VIIRS image of A-76 on 16 May 2021. This false-color image is based on brightness temperature from the "I5" (10-12 micron) band of VIIRS. A-76 is in the center of the image, with sea ice below it and cloud cover on the right. Courtesy of the Colorado State University's Cooperative Institute for Research in the Atmosphere (CIRA) and the NOAA Regional and Mesoscale Meteorology Branch (RAMMB).

Figure 3: Sentinel-1A image of A-76 on 13 May 2021. Note that the orientation is opposite that of Figures 2 and 4. Courtesy of the European Space Agency.

While A-76 is very large, it is only about one-third the size of the biggest iceberg in recorded history. That record belongs to an iceberg named B-15 that calved off of Antarctica’s Ross Ice Shelf 21 years ago. Iceberg B-15 measured a surface area of around 11,000 square kilometers (4,200 square miles), larger than the whole island of Jamaica.

A-76 is not thought to be a direct result of climate change. Calving of ice shelves is a natural process, part of the hydrological cycle. Ice sheets and glaciers are fluid, always moving forward if there is an accumulation of snow in their upper reaches. This is a fast-moving part of the ice sheet. It’s a part of the ice shelf that has been growing out over the ocean for decades. The iceberg will not add to sea level rise as it melts because, as floating ice, it is already displacing the same volume of water that it will add as it melts. It will have some impact on salinity, given that ice sheets and glaciers are freshwater ice.

The question with A-76 is what will happen next. An iceberg about 100 miles long and 30 miles wide that had broken off from the Antarctic Peninsula in 2017 raised alarm in November when it appeared to be on a collision course with the British island territory of South Georgia. That iceberg, A-68a, ended up grounding off the island’s coast. If A-76 hits a similar current, it could reach the Antarctic Peninsula within months and could interfere with shipping lanes. A-76 is already changing. Figure 4 shows two pieces that broke off the large iceberg on 25 May.

Figure 4: VIIRS animation of A-76, 25-27 May 2021, showing breakaway of two smaller icebergs. Imagery from CIRA.

In the News:

• ESA
• US National Ice Center
• BBC
• EarthSky
• CNN

¹West Antarctica is the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere.

²According to the US National Oceanic and Atmospheric Administration (NOAA), the US National Ice Center (NIC) is the only organization that names and tracks all Antarctic icebergs. The “A” in the name refers to the quadrant of Antarctica; the numbers are sequential for icebergs that have occurred in that quadrant.