Climatic-change implications from long-term (1823-1994) ice records for the Laurentian Great Lakes

Long-term ice records (1823-1994) from six sites in different parts of the Laurentian Great Lakes region were used to show the type and general timing of climatic changes throughout the region. The general timing of both freeze-up and ice loss varies and is driven by local air temperatures, adjacent water bodies and mixing, and site morphometry. Grand Traverse Bay and Buffalo Harbor represent deeper-water environments affected by mixing of off-shore waters; Chequamegon Bay, Memnominee, Lake Mendota, and Toronto Harbor represent relatively shallow-water, protected environments. Freeze-up dates gradually become later and ice-loss dates gradually earlier from the start of records to the 1890s in both environments, marking the end of the 'Little Ice Age.' After this, freeze-up dates remained relatively constant suggesting little change in early-winter air temperatures during the 20th century. Ice-loss dates at Grand Traverse Bay and Buffalo Harbor (but not at the other sites) became earlier during the 1940s and 1970s and became later during the 1960s. The global warming of the 1980s was marked by a trend toward earlier ice-loss dates in both environments.