A23a, World's largest iceberg.

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A massive iceberg has calved from the western side of the Ronne Ice Shelf, which is located in Antarctica's Weddell Sea. The iceberg, known as A-76, is around 4320 square kilometers in size, making it the world's largest berg at the moment.

Recent pictures from satellites show an iceberg about three times the size of New York City floating past the northern tip of the Antarctic Peninsula. According to the British Antarctic Survey, the berg known as A23a is now likely to be pushed along by the Antarctic Circumpolar Current into 'iceberg alley.' A23a, which once housed a Soviet research outpost, broke away from West Antarctica's Filchner-Ronne Ice Shelf in 1986.

Traditionally, icebergs are called by the Antarctic quadrant in which they were first observed, followed by a sequential number and, in the event that the iceberg fractures, a sequential letter. You can click this link to view an animation that depicts the iceberg breaking off the Ronne Ice Shelf. 

As of March 2000, iceberg B15—which broke off from Antarctica's Ross Ice Shelf—measures roughly 300 km in length and 40 km in width (186 x 25 mi), with a surface area of 11,000 km2 (4,250 sq mi). This iceberg is the largest one that can be properly estimated using satellite photography.