An Antarctic iceberg about six times the size of Manhattan has broken off to cruise toward the Southern Ocean, where scientists fear it will be difficult to track during the Antarctic winter.

Researchers sometimes track dozens of icebergs at a time. About a third of a mile thick, Iceberg B31 has been one to watch, CNN reported.

A crack first spotted in 2011 caused the 255-square-mile iceberg to split off from Antarctica's Pine Island Glacier in the fall, when it started drifting.

"The iceberg is now well out of Pine Island Bay and will soon join the more general flow in the Southern Ocean, which could be east or west in this region," iceberg researcher Grant Bigg from the University of Sheffield in England said in the NASA statement.

The floating ice sheet will be difficult to spot for the next six months as winter darkness envelops Antarctica, NASA said in an Earth Observatory report.

It's one that's large enough that it warrants monitoring," NASA glaciologist Kelly Brunt told Reuters on Wednesday. While an iceberg of that size could affect shipping, Brunt wasn't concerned about Iceberg B31 yet.

"There's not a lot of shipping traffic down there. We're not particularly concerned about shipping lanes. We know where all the big ones are," she told Reuters.

Scientists have also been keeping a close eye on where the iceberg originated since Pine Island Glacier is believed to be shrinking and could potentially contribute to sea rise.

For now, researchers will keep an eye on Iceberg B31. According to Robert Marsh, a scientist at the University of Southampton in England, a chunk of ice that size can hang around for a year or even longer.

"It's like a large sheet cake floating through the Southern Ocean," Brunt described.

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