The ability
of a body of water to store heat is due primarily to the heat capacity
of its water. Water has a specific heat of 1.0 calories per gram per
degree Celsius. This means that it takes 1 calorie of heat energy
to raise the temperature of a gram of water by 1°C. For
example, using the data from Lake Independence on April 6, 1998 (8
days after ice-out) at 6 a.m. we can calculate the heat content of
the upper layer, where
heat content
= mass x specific heat x temperature (m * C * delta T )
=
(grams) x (calories/gram/degree) x (degrees °C)
And since
Mass of water = density x volume and density = 1 gram/milliliter which
= 1 kg/Liter,
Heat content
= volume x density x specific heat x temperature
(m * C
* deltaT ) = (liters x kg/Liter) x (calories/gram/degree) x (degrees°C)
|
Layer
|
Volume
(x 105 m3)
|
Temperature
(average of layer)
|
Heat
(calories per layer)
|
|
0-1
meters
|
3.29
|
6.44
|
2.12
x 1012
|
|
1-2
meters
|
2.87
|
6.31
|
1.81
x 1012
|
|
2-3
meters
|
2.62
|
6.24
|
1.63
x 1012
|
|
Total
(0-3 m)
|
8.78
|
|
5.56
x 1012
|
Large
bodies of water can modify the weather in their region by their ability
to store heat energy during warm periods and release it during cooler
times. For instance in Duluth, Minnesota, the weather forecasts typically
say "cooler by the lake" in summer because the average surface
temperature of the lake is only about 10°C (50°F) then,
and "warmer by the lake" in winter because its average temperature
is about 4°C (39°F) which is much warmer than the
air.
We can
follow trends in the lake's "heat budget" by computing the
heat content of its layers relative to their minimum values at 0°C.
This is the subject of a specific Studying
Heat Budgets Lesson and the Investigating
Heat Budgets Lesson. Further discussion of the heat balances of
lakes can be found in standard limnology and geosciences texts (e.g.
Horne, A.J. and C.R. Goldman 1994. Limnology, 2nd
edition. McGraw-hill, Inc.).
OXYGEN
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