A vocabulary of landscape — a landscape of words
1367 entries
thermocline
A thermocline is the layer in a body of water where temperature changes sharply with depth, separating warm surface water from cold deep water. In a lake in summer, it can be a few feet thick with a difference of twenty degrees across it, and it acts as a barrier: The two layers do not mix, so oxygen is not carried down and nutrients are not carried up until the whole column turns over in autumn.
Etymology
The word is Greek for a heat slope and it was coined in the late nineteenth century, in the same period that produced limnology, when the physics of lakes was first being measured systematically. Its relatives are named the same way: a halocline is a sharp change in salinity and a pycnocline a sharp change in density.
Notes
Anglers and divers meet it directly. Fish concentrate at or just above the thermocline in summer because it is where the temperature suits them and the oxygen is still adequate, and a depth sounder often shows it as a distinct line. Sound reflects and refracts off it too, which is why submarines have used it for concealment and why sonar performance changes with the season.