Ah, finally broken loose. There was speculation about it before winter.
These events happen every few years and often they are much larger than this one. They are being used by the AGW crowd to somehow mask the fact that the Antarctic is growing - since satellite imagery started in 1979, the Antarctic has been growing steadily, year by year. You don't hear about it because it kinda ruins the whole AGW image they like to tout.
These 'islands' break off due to pressure from ice further inland; some have been 3 times the size of this one. The ice 'slides' down the slope because pressure forms a liquid layer between the ice and the land under it, making it like a friction free ramp. Eventually it gets enough sea under it that the weight 'cantilevered' out over the depths forces the ice to break off.
They do seem to have been happening, or more likely being reported, more often, but if so, that is a sign of the growth of the ice further inland, and not of warming.
Would have been nice if they'd planted a camera or two there so we could see the event in real time. Must be awesome watching the sudden rift appear.