The Structure of the Spring Thermal Bar in Lake Superior,II

The thermal bar was studied during May and June of 1974 and 1975 near the Keweenaw Peninsula along the south shore of Lake Superior. Temperature distributions and the distributions of naturally fluorescent material were measured in order to determine the nature of the energy and mass transport in the thermal bar zone. Transects were located perpendicular to the thermal bar, and temperature was measured at 5 m intervals to a depth of 45 m using a thermistor probe with a 3 sec time constant interfaced with a signal conditioner and digital voltmeter. Accuracy in the range of 4°C was ± 0.01°C. Water samples were collected, and the natural fluorescence arising from land runoff was measured. Station locations were determined by triangulation. Data for both temperature and fluorescence were plotted by a computer mapping program (SYMAP).The computer plotted temperature distributions provide the most detailed picture of the thermal bar thus far obtained. The complexity suggests considerable turbulence. A strong correlation between natural fluorescence and temperature supports the concept that little mixing occurs between inshore and offshore waters and that a significant portion of inshore water arises from runoff. The bottom slope seems to have a strong influence on the flow near the thermal bar and on the rate of movement offshore.