Meromictic Lake
(c) 2002 Andrew Alden, licensed to About.com, Inc. (fair use policy)
Round Lake, near Syracuse, New York, is a meromictic lake, a lake whose waters do not mix. Because the rocks around it contain beds of salt, its bottom waters are a layer of strong brine. Its surface waters are devoid of fish, instead supporting an unusual community of bacteria and algae that give the water a peculiar milky blue-green color. Meromictic lakes are common in the tropics but quite rare in the temperate zone.
Most lakes in the temperate zone turn their waters over every autumn as the water cools. Water reaches its greatest density at 4 degrees above freezing, so it sinks when it cools to that temperature. The sinking water displaces the water below, no matter what temperature it's at, and the result is a complete mixing of the lake. The freshly oxygenated deep water sustains fish throughout the winter even when the surface is frozen over. See the Freshwater Fishing Guide for more about the fall turnover.
Because the bottom of Round Lake is so stable, the sediments that accumulate there are exceptionally well-preserved records of the plant species growing in the region as well as the changing aquatic community in the surface layers. Geographically, it sits on the border between two great weather systems separated by a jet stream in the upper atmosphere. This makes it very sensitive to subtle climate changes that have occurred during the last 10,000 years since the glaciers left. Round Lake is preserved in Green Lakes State Park. Another example of a meromictic lake is Soap Lake in Washington state.
Fossils
Geologic Features and Processes
Glaciers and Ice
Landforms
Minerals
Rocks
Geology and Society
