Think about the consequences for life and climate if ice were denser than water. Instead of floating at the surface, it would sink to the depths, and lakes would fill with ice each winter from the bottom up, eventually providing no liquid water in which fish and other animals could seek refuge. In deeper lakes, it is logical to assume that ice could remain at depth all year long, perhaps not melting, except for small puddles, even in the shallows. Not only would this lead to very different aquatic species inhabiting higher latitude lakes, but the local climate would be greatly altered wherever very cold water bodies remained through the warmer seasons.
Completing the cycle, with spring warming the ice melts and cold surface waters warm until they reach the temperatures of the bottom waters, again producing a fairly uniform temperature distribution throughout the lake. When this occurs, winds blowing over the lake again set up a full circulation system, this mixing known as spring turnover. As the warming continues, the three water layers again become established, and our cycle has been completed.
Copyright 2003, Keith C. Heidorn, All Rights Reserved. (Illustrations ©Spectrum Educational Enterprises, All Rights Reserved.)
