I'm pretty sure I've heard of the Southern Ocean before. It also seems a little fishy that this is being heavily promoted by the magazine that (presumably) these 'Nat Geo cartographers' work for.
Is this a PR stunt? Is there an official body that classifies oceans?
Edit:
I guess this bit of the article explains it. There is no new ocean, it's been recognised for a while.
"'The Southern Ocean has long been recognized by scientists, but because there was never agreement internationally, we never officially recognized it,' says National Geographic Society Geographer Alex Tait. "