Posts: 41
Location: Minneapolis, MN | Some Cliff Clavin factoids:
A thermocline(s) is a distinct layer(s) of cold water and is not a gradual change in temperature the deeper you go. If you’ve ever snorkeled or dived in lakes with thermoclines, you can actually see the shimmering layer of cold water because of the difference in density. Turn over occurs when the upper layers of water becomes colder (and more dense) than the deeper water and sinks.
Mille Lacs will form a thermocline at times when the sun shines, the air is hot and there is little or no wind. Because it’s so big and shallow, when the wind blows, all the layers mix. And technically w/out a thermocline a lake cannot turn over. So I guess it's constantly "turning".
Edited by MuskieSlayer 9/19/2003 1:07 AM
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Posts: 32927
Location: Rhinelander, Wisconsin | If a lake has no distinct thermocline the temps will still be much warmer on the surface before the turn. The angling reference to what happens in the fall when surface temps cool dramatically and the top of the water column 'sinks' and mixes with with the bottom of the column until top to bottom the temps are the same is 'turnover'. After that process is complete and the water continues to cool before ice-up, water clarity usually improves. Fish have no temperature gradients to move towards or from, or a lower oxegen level if the lake did stratify. From a good source document: Any lake will have similar turnover and stratification patterns from year to year, assuming weather conditions are near normal. Also, lakes which have similar depths, fertility and exposures to prevailing winds will tend to have similar turnover and stratification patterns. All lakes turn over, but not all of them stratify strongly. Some shallow lakes contain warm water from the surface to the bottom, and even deep lakes do not significantly stratify if they are exposed to strong winds wich can continually circulate the water. http://www.conservation.state.mo.us/fish/ponds/laketurn/ |
