A-76 emerged from the Ronne Ice Shelf, located near the base of the Antarctic Peninsula.
It is one of several to have come from the outcrop over the last few years, but not a direct result of climate change.
Ted Scambos, a research glaciologist at the University of Colorado at Boulder said its presence would not raise ocean levels.
A-76 blows past the former largest, its neighbour A-23A, by more than 300 square miles.
A-23A is roughly 3,380 square km (1,305 square miles) in size and also broke into the Weddell Sea.