As a result, the thermal stratification is terminated. Thus the annual cycle brings the deep water to the surface where it is enriched with oxygen. Moreover, the nutrients in the hypolimnion also get mixed with the water in the epilimnion.
In winter again a stable stratification occurs. The hypolimnion contains water at or near 4°C, which has a higher density and the epilimnion has colder, less dense water or ice above. This situation prevents turbulent mixing. Again in spring the surface water warms to 4°C leading to a mixing.
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