Douglas Harper's Etymology Dictionary
Wiktionary
n. (context geography English) A layer within a body of water or air where the temperature changes rapidly with depth.
Wikipedia
A thermocline (sometimes metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water, such as an ocean or lake, or air, such as an atmosphere) in which temperature changes more rapidly with depth than it does in the layers above or below. In the ocean, the thermocline divides the upper mixed layer from the calm deep water below. Depending largely on season, latitude and turbulent mixing by wind, thermoclines may be a semi-permanent feature of the body of water in which they occur or they may form temporarily in response to phenomena such as the radiative heating/cooling of surface water during the day/night. Factors that affect the depth and thickness of a thermocline include seasonal weather variations, latitude and local environmental conditions, such as tides and currents.
Usage examples of "thermocline".
Located below the thermocline, where increase in depth correlates to decrease in temperature.
Below the 612 DAVID HAGBERG seasonal thermocline, but still well above the permanent layer.
Either the sub had bugged out, or it was hiding beneath the seasonal thermocline, which around here was at about nine hundred feet.
Below this artificial thermocline, the life of the Pacific ebbed and flowed normally.
Those waves that did manage to penetrate the thermocline were mostly trapped below it.
The second surface was the thermocline, the invisible division between the colder waters of the bottom and the warm, light waters of the sky.
During the height of the warm weather, the thermocline was definite enough a division as to make for good sledding and for chilly passage.
Man, too, passed freely between the two countries of water which were divided by the thermocline, though many of the creatures with which he lived could not pass that line at all, once it had established itself.
The thermocline held here beneath the rig, but she was moving the sub slowly, stealthily, and merely noted the temperature rise as she passed two hundred feet.
The ocean is not really one ocean, but two -- a top and bottom layer, with a boundary layer approximately one kilometer below the ocean surface, called the thermocline, through which very little vertical transport takes place.
During the height of the warm weather, the thermocline was so definite a division as to make for good sledding and for chilly passage.
Below the thermocline, down around forty feet, it would get a lot colder and a lot darker.
It was most comfortable in a range between 40 and 55 degrees Fahrenheit, and as it drifted with the currents and encountered thermoclines and upwellings that warmed or cooled the water, it moved up or down.
Walking east, you cross abrupt thermoclines as you move between the cool shadows of tall buildings and brief regions of direct sunlight.
Fine grains of ice flew through the room like shrapnel, propelled by the impossibly steep thermoclines sweeping the city.