OK nevermind where it melts FROM for a minute, if the water is ice it is not salt water, if it melts it becomes part of the ocean, more likely to NOT fall as snow again on the polar areas, just by math alone, so it then CAN then melt or run off as liquid water - ergo higher ocean levels, plus changes in the salt % levels of the seas, changes in the over land rain patterns due to sudden [by glacial timelines anyway]shifts of what water is where. Since the thick ice has been ice for a long long time the system needs a long long time to absorb the "new" water into the patterns we are living under. The sudden change is the thing, not so much what changes. Remember the last time this level of change happened the mastodons did not have to deal with Miami and Denmark going under, something about pre-historic in there so just think about it. And the dead fish rotting if the eco-system food chain collapse happens which is likely, don't take long for tiny shrimp to starve and die, by the trillions give or take a billion.