Iceberg A-74 Calves from the Brunt Ice Shelf in the Weddell Sea

By LT Falon M. Essary, USN
U.S. National Ice Center
March 01, 2021

Suitland, MD — The U.S. National Ice Center (USNIC) has confirmed A-74 has calved from the north facing side of the Brunt Ice Shelf. The much anticipated break was first reported on the 26th of February by GPS equipment, but not confirmed until 27th of February via Sentinel-1A imagery. As of the 28th of February, the new iceberg A-74 was located at 75° 13' South, 25° 41' West and measures 30 nautical miles on its longest axis and 18 nautical miles on its widest axis. The western part of the shelf which was first identified as the next potential large iceberg to calve from Brunt due to several large crevasses running through it remains intact.

A-74 was first reported by the British Antarctic Survey, and confirmed by USNIC Ice Analyst Christopher Readinger using the Sentinel-1A image shown below.

Iceberg names are derived from the Antarctic quadrant in which they were originally sighted. The quadrants are divided counter-clockwise in the following manner:

A = 0-90W (Bellingshausen/Weddell Sea)
B = 90W-180 (Amundsen/Eastern Ross Sea)
C = 180-90E (Western Ross Sea/Wilkesland)
D = 90E-0 (Amery/Eastern Weddell Sea)

When first sighted, an iceberg’s point of origin is documented by the USNIC. The letter of the quadrant, along with a sequential number, is assigned to the iceberg. For example, C-19 is sequentially the 19th iceberg tracked by the USNIC in Antarctica between 180-90E (Quadrant C). Icebergs with letter suffixes have calved from already named icebergs, where the letters are added in sequential order. For example, C-19D, is the 4th iceberg to calve off the original C-19 iceberg.

The National Ice Center is a tri-agency operational center represented by the United States Navy (Department of Defense), the National Oceanic and Atmospheric Administration (Department of Commerce), and the United States Coast Guard (Department of Homeland Security). The National Ice Center mission is to provide the highest quality strategic and tactical ice services tailored to meet the operational requirements of U.S. national interests and to provide specialized meteorological and oceanographic services to United States government agencies.

Satellite image of Iceberg A-74
Figure 1: Sentinel-1A image of A-74, February 28, 2021 (Sentinel-1A courtesy of ESA)

For more information, please contact:
National Ice Center
Command Duty Officer
Voice: (301) 943-6977
Twitter: @usnatice
Facebook: @usnatice

The U.S. National Ice Center is a tri-agency center operated by the Navy, NOAA, and Coast Guard and provides global to tactical scale ice and snow products, ice forecasting, and related environmental intelligence services for the United States government.

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