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Race for Northernmost Drifting Antarctic Iceberg Ends in a Tie

Tuesday, August 20, 2019

On February 4, 1979, an iceberg slightly larger in area than the city of Indianapolis was first spotted in the Wilkesland Sea after breaking off (or “calving”) from Antarctica. Eleven years later, the giant chunk of ice known as C-02 had drifted farther north than any other in recorded history… until now.

Image courtesy of NOAA/Dr. Robert Ricker

Researchers who specialize in tracking icebergs have found a contender that is now vying for the title, named A-57a. Coming in at around one-third the size of C-02 (or roughly the size of Kansas City in area), this iceberg calved on May 26, 2008 from the Ronne Ice Shelf and was last seen more than 930 miles east of C-02’s last known position, which had been about 570 miles off Punta Delgada on the eastern coast of Argentina. However, both made it about the same distance north, to around 42.5 degrees south latitude.

Icebergs, or large pieces of ice that have broken off from a glacier or ice shelf, are a common sight in polar regions as they float (or sometimes run aground) in the frigid water. Around Antarctica they are named after where they originate as well as the sequential number in which they calve. For example, researchers divided Antarctica into four quadrants (A, B, C, and D). A-57a was the 57th iceberg to break off the continent’s A-quadrant since tracking began in the early 1970s. It further broke into a second iceberg (A-57b), which kept breaking up and eventually deteriorated. C-02 was the second iceberg to break off the C quadrant since tracking began.

According to Christopher Readinger, an analyst with the US National Ice Center who studies the movements of icebergs, they can float up to 200 nautical miles (roughly 230 miles) per week. 

“The icebergs are primarily ocean current-driven,” said Readinger, “but about two-thirds of the ones we are watching are actually grounded, stuck on the bottom near the shore.” In fact, A-57a actually sat right next to where it calved for years before finally drifting away. 

Readinger and his colleague, Sofia Montalvo, said they are currently tracking 41 icebergs in total using a combination of high-resolution visible and infrared imagery from the VIIRS sensors onboard NOAA-20 and Suomi-NPP as well as data from the Synthetic Aperture Radar (SAR) satellites, which can see through both clouds and darkness.

A view of iceberg A-57a from NOAA-20 on July 30, 2019, visible through the clouds off the Eastern Coast of Argentina. You can see a smaller piece has broken off, which continued to deteriorate. 

“The southern icebergs are ridiculously massive compared to the northern ones that come from glaciers in Greenland, which are usually pretty small in comparison—around a quarter-mile square or so,” he explained. “Antarctic icebergs are often so large they are compared to city or state sizes, such as Connecticut or Delaware.”

However, once these icebergs break apart or shrink to 20 square nautical miles (~26.5 square miles) in size, they are considered too small to continue tracking. This can take years or decades to happen. “We could keep tracking the smaller pieces, which are still huge,” Readinger laughed, “but we have to draw the line somewhere.” If his team tracked anything smaller, they’d be watching hundreds and maybe thousands of icebergs.

Montalvo explained that most of the drifting icebergs that they are keeping an eye on are moving in the normal directions they typically see, following the currents.

As far as why these two massive icebergs made it so far north from their home in the Antarctic, Readinger offered a guess. “I’m not an oceanographer, but perhaps they just happened to hit exactly the right point in the Antarctic circumpolar current to shoot up north.” He added that this current usually runs from west to east, but there may have been a kink in it, or eddies, since the currents themselves generally tend to stay pretty consistent. 

C-02 is long gone, but as of February 1990, its last tracked coordinates (before it was too small) were 42.5S, 52.5W. The last tracked coordinates of A-57a were 42.57S, 33.92W on Aug. 3, 2019. 

The last tracked locations of C-02 and A-57 were roughly the same distance north from Antarctica.
Image courtesy of Google Maps

This may indicate that C-02 was the record-winner, but Readinger pointed out that “in 1990, they did not have the fancy GIS systems we use today, so their measurement is most likely rounded off.” Thus, whether or not one inched slightly farther than the other, the world may never know.