Difference about Great Lakes aren't ocean but just an huge lakes since the ice in Arctic and Antarctica are just along with ocean so sea level rises when ice is melting in the ocean.
Remember about ice in Arctic is shrinking for several years, probably until 2007 before rebound so sea level rises when very larger of ice is melting.
I can imagine about what happens to the ocean when entire of ices are gone but won't happen in many years or whatever is interfere with environment.
