High Resolution Imagery Assists in Discovering Icebergs,
Named A-56, A-57 and Wilkins Ice Shelf Continues to Collapse
Last Update: August 19, 2008

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Figure 1. ENVISAT Image 30 May 2008, A-56, A-57 fasted along Ronne Ice Shelf.

(Please click on the pictures to view the larger image)

May 30, 2008, Washington D.C. -- The National Ice Center (NIC), using high-resolution ENVISAT imagery, identified two icebergs fasted along the Ronne Ice Shelf just to the west of Berkner Island. Both these icebergs meet criteria for naming and tracking by the NIC. With the advent of higher resolution imagery in tracking procedures at the NIC, we were able to document two icebergs previously obscured by clouds or indistinguishable from its neighboring glaciers. The first iceberg was named A-56, being the 56th occurrence that an iceberg has calved within 0 and 90W. It is located at 77.04S 50.21W and measures 14NM long and 07NM wide. The second iceberg was named A-57, being the 57th occurance an iceberg has calved within 0 - 90W. It is located at 77.37S 48.45W and measures 19NM long and 05NM wide. ENVISAT imagery indicated the presence of A-56 and A-57 on 30 May 2008 (Figure 1) and clearly shows both icebergs fasted along the Ronne Ice Shelf . Both icebergs are currently stationary within the fast ice and forecasted to remain for the foreseeable future.

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 (Bellinghausen/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 NIC. The letter of the quadrant, along with a sequential number, is assigned to the iceberg. For example, A-53 is sequentially the 53rd iceberg tracked by the NIC in Antarctica between 0-90W (Quadrant A).

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 worldwide operational ice analyses for the armed forces of the United States and allied nations, U.S. government agencies, and the private sector.

WILKINS ICE SHELF CONTINUES TO COLLAPSE

June 05, 2008, Washington D.C.-- Ice analysts at the National Naval Ice Center (NIC) continue to monitor changing conditions along the Wilkins Ice Shelf in the Bellingshausen Sea, and have identified that another major portion has collapsed, or calved. Multiple icebergs produced by this calving event could pose hazards to maritime interests in the future. Comparisons of high resolution ENVISAT imagery (figures 1-3) clearly show another major portion of the shelf breaking off and advecting into the pack ice. This entire portion measured over 71 square miles before its collapse.

The previous calving event occured in early March, 2008. A subsequent collapse was not previously expected during this austral winter. However, despite winter freeze conditions developing throughout Antarctica, a combination of winds, diurnal effects, thin surrounding pack ice, and structural flaws within the ice shelf led to this recent calving event. The speed at which this event occured goes to prove the weaknesses within the entire Wilkins Ice Shelf. Based on this information, future collapse or calving events remain possible.

Aerographer's Mate Kevin Heisler identified the collapse through a comparison of ENVISAT imagery from 15 May 2008 (figure 2) and 31 May 2008 (figure 3). A present image from 03 June 2008 (figure 4) shows continued advection of icebergs into the surrounding pack ice. The largest of these calved icebergs measures 5 nautical miles long.

For more information, please contact:
National Ice Center
Naval Ice Center
Liaison Branch
Voice: 301-394-3100
E-mail: liaison@natice.noaa.gov