thermocline

[jim]

is there a thermocline present all year long in a lake or is it present at certain times

[Eyez]

That depends on the lake. Some lakes don't form thermoclines at all, because they're shallow enough to be completely stirred by wind and wave action. Thermoclines usually form in deeper lakes, after there has been sufficient time for the upper layers of the water column to warm to a point that creates an area of rapid change in water temp (thermocline). Thermoclines disappear during the fall turnover when the surface water cools enough to be denser than water below it, and causes it to sink, mixing the water column to where the water is nearly the same temp from top to bottom.


Eyez

[Gunga Din]

It sets us good in winter and summer. During spring and fall turnover, there is no thermocline as the lower and upper water in the column are mixed. Thermoclines do not exist in shallow lakes where the wind action continually mixes them.

[Hans]

The thermocline (assuming we're talking of northern lakes here) is a summer creature. Basically it is a temperature barrier (cold water is heavier than warm water) which prevents "mixing" between the epilimnion (upper) and the hypolimnion (lower) segments of the water column.

In shallow lakes, because wind action causes mixture of the water, it almost never gets a chance to form.

In deep lakes it disappears in the fall, as the surface water cools and sinks, causing an effect called "turnover", which wipes out the "layering" by mixture similar to the action of the wind on shallower lakes.

From fall until midsummer, in all but the deepest lakes, there is likely no thermocline because the water temperature is pretty even throughout the water column. It is only the constant sun of summer which heats the upper part of the lake enough to cause the stratification.

Hans