Dimictic lake

In the spring and fall, these temperature differences briefly disappear, and the body of water overturns and circulates from top to bottom.

This results in dimictic lakes have a strong thermal stratification, with a warm epilimnion separated from the cold hypolimnion by the metalimnion.

[7] Due to the stable density gradient, mixing is inhibited within the thermocline,[8] which reduces the vertical transport of dissolved oxygen.

[9] Long period internal waves in larger lakes can be influenced by Coriolis forces (due to the Earth's rotation).

[12][13] In late summer, air temperatures drop and the surface of lakes cool, resulting in a deeper mixed layer, until at some point the water column becomes isothermal, and generally high in dissolved oxygen.

Thus during Winter II, the major heat flux is now from above, and the warming causes an unstable layer to form, resulting in solar driven convection.

[5][17][3] This mixing of the upper water column is important for keeping plankton in suspension,[18][3][19] which in turn influences the timing of under-ice algal blooms and levels of dissolved oxygen.

Cycles of thermal stratification in a dimictic lake.
There is a seasonal cycle of thermal stratification with two periods of mixing in spring and fall. Such lakes are termed "dimictic'. During summer there is a strong thermal stratification, while there is a weaker inverse stratification in winter. (Figure modified from [ 2 ] )