thermocline

A steep temperature gradient that exists in the middle zone (the metalimnion) of a lake and gives rise to thermally induced vertical stratification of the water. The metalimnion lies between the relatively warm epilimnion above and the cold hypolimnion below. The thermocline may represent a temperature change of 1°C for every incremental depth of 1 metre of water. It may be short-lived, especially in shallow lakes where wind action can mix the water from different levels. However, it can exist for most of the summer period in temperate lakes and sometimes nearly all year in tropical lakes. A thermocline can speed up the process of eutrophication by preventing the diffusion of oxygen from the epilimnion to the hypolimnion (see eutrophic).