It's also abut flow and how the water mixes with the huge amount of water already in the Hudson's Bay and Arctic ocean. There's also the salinity issue, fresh water freezes at a higher temperature, so even if it's warmer going into the ocean, it could actually cool things down a bit by freezing sooner and acting to reflect more sunlight. Open water absorbs about 90% of sunlight and clean ice reflects about the same amount.
But but but...........don't forget the Harper effect.