Page 38 - Oceans

.
36

HEAT AND LIGHT

The oceans are warmed by the Sun, but tropical oceans are

warmed far more than polar seas. Ocean currents redistribute
this heat around the globe, which makes the polar
regions warmer and the tropics cooler. Ocean water
also warms up and cools down slowly, so it never
gets as hot or cold as the land. Even sea ice is Sun's rays
dispersed and
warmer than the ice formed on land. However, weakened near
the poles
heat and light do not penetrate into the ocean
depths, which are permanently cold and dark.

Heating tHe oceans >
The Sun shines down directly on the tropics, warming
the surface water of tropical oceans to temperatures of 86°F
(30°C) or more. Closer to the poles, sunlight is spread out over
a broader area, weakening its power even in summer. Sun's rays
The polar oceans get so little sunlight in winter that concentrated in
they freeze over, creating vast expanses of sea ice. the tropics

< ocean temperatures
Warm tropical water, The surface water of oceans is warmest in the
with temperatures tropics and coldest near the poles. But the water
constantly above
77°F (25°C) in the ocean depths is always just above freezing
point, even near the equator. Despite this, the
total range of ocean temperature is only about
90°F 32°C 104°F (40°C), compared to the temperature
30°C
range of 295°F (146°C) on the continents.

70°F Temperate region
20°C of variable surface Constantly cold polar water
temperatures, with surface temperatures Constantly
ranging from 45– of 32–37°F (0–3°C) cold water
50°F 10°C 68°F (7–20°C) off Greenland
North
Constantly warm America
pool of water in
the Caribbean Sea
30°F 0°C

Warm surface
temperature and layers > water
As ocean water is warmed by the Sun,
it expands and becomes less dense. This makes
it weigh less, so it floats on top of colder, denser
water. The warm surface water is divided from Thermocline
deeper, cooler water by a boundary called the
thermocline, which exists all year round in the
tropics. It stops deep water from mixing with
surface water. As a result, plant nutrients cannot
reach the sunlit surface to fuel the growth of
microscopic plankton. This is why tropical oceans Cold bottom water at a uniform
are so clear. In colder oceans, the thermocline temperature of 36°F (2°C)
breaks down in the fall, allowing nutrients to the
surface where they support far more life.