Mean circulation in the Great Lakes

In this paper new maps ar-e presented of mean circulation in the Great Lake s, employing long-term current observations from about 100 Great Lakes moor ings during the 1960s to 1980s. Knowledge of the mean circulation in the Gr eat Lakes is important for ecological and management issues because it prov ides an indication of transport pathways of nutrients and contaminants on l onger time scales. Based on the availability of data, summer circulation pa tterns in all of the Great Lakes, winter circulation patterns in all of the Great Lakes except Lake Superior, and annual circulation patterns in Lakes EP-ie,: Michigan, and Ontario were derived. Winter currents are generally stronger than summer currents, and therefore, annual circulation closely re sembles winter circulation. Circulation patterns tend to be cyclonic (count erclockwise) in the larger lakes (Lake Huron, Lake Michigan, and Lake Super ior) with increased cyclonic circulation in winter. In the smaller lakes (L ake Erie and Lake Ontario), winter circulation is characterized by a two-gy re circulation pattern. Summer circulation in the smaller lakes-is differen t; predominantly cyclonic in Lake Ontario and anticyclonic in Lake Erie.