Of course it floats. But that's not what I was trying to say. Go to your cup, put some ice in it and then mark the water level. Now let the ice melt and remark the water level. They will be at the same level.

What happens when you add an ice-cube? That's what happens when ice slides off of continents.

A break-up this huge may not directly alter sea-levels but it's certainly symptomatic of a larger disruption that's playing out on a massive scale.