Alpena (ălpē`nə), city (1990 pop. 11,354), seat of Alpena co., N Mich., on Thunder Bay, an arm of Lake Huron; inc. 1871. Limestone quarried nearby is used to make cement, Alpena's chief manufacture. Cement and limestone are transported on the Great Lakes by way of Alpena's harbor. The city lies in a year-round resort area and has an annual winter carnival. The Great Lakes Maritime Heritage Center is there, and a marine sanctury encompassing Thunder Bay and nearby waters preserves more than a hundred shipwrecks.