The deep water of a lake's profundal zone is called the ________. epilimnion Water temperature is briefly uniform at all depths, and winds create vertical currents during the ________. spring overturn At the ________, water temperature changes abruptly over a narrow depth range. thermocline The epilimnion cools, becomes denser, and sinks, eliminating the thermocline during the ________. hypolimnion The top layer of the limnetic zone is called the ________, and is heated by the sun in summer. fall overturn