Lake Temperature Strata
Why does the temperature change when you swim across a
lake? Does it have anything to do with depth or pressure?
The change in temperature of the lake water is mostly because
of depth of the water. The sun and warm air cannot warm deeper
water as quickly because there is more mass of water to warm.
A greater differential in temperature is found vertically, from
then top to the bottom of the lake. Warm water tends to rise,
so the water warmed at the surface of the lake by the sun and
air tends to stay there and not mix with the cooler water below,
unless physically mixed by strong winds. The difference in
temperature from bottom to top is proportional to the depth.
Normally, the greater the depth, the lower the temperature
(aside from lakes with geothermal sources, or springs underneath).
The layer of water between the warm surface water and the
cold water at the bottom is called the thermocline.
Meteorologist at Argonne Nat. Lab.
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Update: June 2012