We don't have many deep lakes in the Chihuahuan Desert, but there are a few places that can demonstrate nicely what people in better watered places have long known. Dive too deep, and suddenly the water is downright cold, and the change is sudden, almost as if there was a line drawn in the water. On one side, sun-warmed water; on the other, more like ice water. This sudden change in temperature is a thermocline, caused by warmer water being lighter in weight than colder water. As the water warms in the spring, the warmer water floats on top, and because of the differences in weight, resists mixing.
This has biological consequences. Without mixing,
deep water is not recharged with the oxygen required by creatures
below the thermocline. And as those above use up vital dissolved
minerals and lose them to deep water in droppings and through
death, the upper waters lose productivity. Luckily, with cooler
weather, the lake waters eventually reach the same
temperature—and then, it takes only a bit of wind to mix it
all up again.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.