Notjonathon,
Yes the sea in those areas is supersaturated with CO2 and so the excess is vented from the surface. It's not in bubble form, but the water and air are trying to get into an equilibrium. Not only does this add extra CO2 but it means that less of the additional human contributed gas will be scrubbed from the atmosphere. It's a double whammy.
The more of these sinks turn into sources the faster that atmospheric CO2 concentration will rise.
As for quantifying it, I don't suspect the value will be huge at the moment. It will be seasonal (only when the ice isn't there), but if, as suggested, the CO2 is coming from the melting permafrost on the seabed then it could be sourcing for thousands of years.....or until we get a major methane blowout in which case it would be a long way down our list of things to worry about.