Two new and very large icebergs broke away from the Ross Ice Shelf in Antarctica earlier this month in a natural “calving” process that returned the edge of the shelf to its pre-exploration position of the early 1900’s, researchers say.
The icebergs were designated C-18 and C-19 by the Suitland, Md.-based National Ice Center (NIC), a joint operation of the U.S. Navy, the National Oceanic and Atmospheric Administration, and the U.S. Coast Guard.
Using data collected from the Defense Meteorological Satellite Program, NIC said that C-19, the larger of the two icebergs, is 199 kilometers (108 nautical miles) long by 30.5 kilometers (17 nautical miles) wide. C-18 is roughly 75.9 kilometers (41 nautical miles) long by 7.4 kilometers (4 nautical miles) wide.
Researchers at the National Science Foundation (NSF)-funded Antarctic Meteorological Research Center (AMRC) at the University of Wisconsin–Madison and meteorologists at McMurdo Station, NSF’s logistics hub in Antarctica, almost simultaneously noticed the break in the Ross Shelf where C-19 calved.
Linda Keller of the university’s department of atmospheric and oceanic sciences noticed the crack while posting daily images on the AMRC Web site. Both the forecasters and the university subsequently notified the National Ice Center.
The AMRC makes daily composite images from weather-satellite data available on the World Wide Web. It also monitors icebergs and has tracked the large iceberg B-15 since it calved in March 2000.
Douglas MacAyeal, an NSF-funded researcher at the University of Chicago, who placed automated weather stations and tracking devices on B-15A, a enormous fragment of the larger iceberg, said that the satellite and other technologies are allowing science for the first time in history to observe the calving of large icebergs like C-19 and B-15. The process, he noted, is part of a natural cycle in which ice shelves grow and then calve icebergs over geological time scales.
Researchers also noted that the developments on the Ross Shelf are markedly different from the process underlying the widely publicized collapse of the Larsen B ice shelf much farther north on the Antarctic Peninsula early this year. While still not fully understood in terms of glaciological history, scientists believe that the Larsen B collapse is tied to a documented temperature increase on the Antarctic Peninsula. NIC reported that another huge iceberg, roughly 30 nautical miles (55.5 kilometers) long by six nautical miles (11.1 kilometers) wide, calved in the Weddell Sea on May 17. It was designated iceberg D-17.
Unlike B-15, which calved from a different point on the Ross shelf, C-19 broke away relatively close to Ross Island, where McMurdo Station is located. B-15A and C-19 are now sitting at right angles to each other, adjacent to Ross Island.
Although the fate of the C-19 is unknown, Charles Stearns, emeritus professor of meteorology at the University of Wisconsin, said the calving brings the Ross Ice Shelf to roughly the size it was in 1911, when members of British explorer Robert Falcon Scott's party first mapped it. Stearns also noted that while the calving of C-19 was fairly rapid, the fissure from which the iceberg broke away from the shelf has been known to scientists since the 1980’s.
For updated satellite images of iceberg C-19 from AMRC, see: http://uwamrc.ssec.wisc.edu/amrc/iceberg.html
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