Water Temperatures in a Shallow Lake During Ice Formation, Growth, and Decay

Continuous water‐temperature measurements were made in a shallow lake in upper Michigan during ice formation, growth, and decay. Just before complete freeze‐over, the temperature of the water from just below the surface to the bottom of the lake reached a minimum of +0.2°C. After a permanent ice cover had formed, the water beneath the ice began to warm up. During a 25‐day period in December, the water temperature near the bottom of the lake increased from +0.3°C to +3.0°C. A quantitative analysis of this heat gain attempts to show that most of it came from the energy stored during the summer in the underlying soils. During the ice‐thaw period in April, the temperature throughout the main mass of water decreased substantially. Since the lake until this time was in a state of quasi‐stable thermal stratification, it was assumed that this cooling resulted from the mixing of meltwater flowing into the lake from surrounding snow.