MONITORING MIDLAKE WATER TEMPERATURE IN SOUTHERN LAKE-MICHIGAN FOR CLIMATE-CHANGE STUDIES

Recent studies of potential climatic change on Great Lakes fisheries ( e.g. Meisner, 1987; Magnuson, 1990; Regier et al., 1990) and our gener al ignorance of the natural variability of the basic physical properti es of the Great Lakes (McCormick, 1990) have demonstrated the need for a long-term observation program which is representative of the lake-w ide environment. In April 1990 a site was established in Lake Michigan to continuously monitor the offshore thermal structure and vertical v elocity profile. The site is located near the center of the lake's sou thern basin in 160 m of water. Temperature is measured at 16 depths (w inter) to 28 depths (summer), and the horizontal velocity components a re measured at 5 levels which allows us to characterize the offshore e nvironment with high temporal resolution. The goals of this effort are to provide basic physical measurements to better describe the flow of energy through the lake ecosystem and to provide a basis against whic h future change can be better gauged.