Measurement of spring thermal stratification in Lake Michigan with the GLUCOS observing system

The GLUCOS buoy-based observing system was deployed in Lake Michigan off the coasts of Milwaukee and Shorewood, WI from April 8 to May 28, 2009 to measure the dynamics of spring stratification. Three radio-linked data acquisition Pioneer buoys were deployed at 20 m, 40 m and 60 m depths approximately 2.1 km, 6.1 km and 9.2 km from shore respectively. Each buoy was equipped with a temperature sensor string to measure the thermal profile and multiparameter sondes to measure temperature, specific conductivity, turbidity, % saturation DO₂, pH and chlorophyll fluoresence. The thermal front, identified by a 4°C vertical isotherm known as the thermal bar, was clearly observed passing each buoy as it moved from shallow to deeper water as the spring wore on. Sonde measurements showed some correlations with the onset of thermal stratification. This paper presents the design of the thermal bar buoy array, the temperature profiles and sonde data and discusses future directions.