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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