In another sign that spring has returned in Michigan, the Great Lakes are now ice-free - having cleared out enough to rank among the top 20 earliest thaws in the last 45 years, researchers said Wednesday. The findings were reviewed by the Ann Arbor-based Great Lakes Environmental Research Laboratory, which is tied to the National Oceanic and Atmospheric Administration. Scientists there have been studying ice cover and related phenomena for decades.According to the group’s Great Lakes Surface Environmental Analysis, “the #GreatLakes were officially ice-free as of Sunday!!! 11th earliest ice-out in the last 45 years,” researchers tweeted.