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LIFE CYCLE OF AN UPWELLING EVENT
When the wind blows along (parallel to) the
coast in shallow coastal areas of the ocean, the surface water can be
blown towards or away from the coast depending on the direction of the
wind. If the warm surface water found along the coast of New Jersey
during the summer is moved away from the coast by winds from the southwest,
colder water from beneath the surface rises up and takes its place.
This event is called an upwelling. Upwelling events along the coast
of New Jersey typically take place during the summer months (May-September).
Here is how an upwelling takes place.
First Stage: Warmer surface water, colder bottom water.
During the summer months, the sun is more
directly overhead for a greater part of the day compared to the winter
months. This increased exposure to the sun heats the water on the ocean's
surface. Much of the heat of the sun is trapped in tiny particles floating
at or near the surface of the water, which keeps the heat from penetrating
and reaching the water closer to the bottom. Therefore, the water closer
to the bottom is usually colder than that found on the surface.
This layering of warm water at the surface and colder water towards
the bottom is called stratification. The difference in temperature between
the layers also creates a difference in density. The water molecules
in the warm water have more room between them than the water molecules
in the cold water. This makes the warm water lighter, or less dense,
than the cold water, which is heavier and sinks below the warm water.
The difference in density makes it difficult for the two layers to mix,
and keeps them separate, or stratified. The narrow area where the two
layers meet, and where the water temperature (and density!) changes
quickly, is called the thermocline.
Second Stage: Warm surface water is
blown offshore; cold seafloor water rises.
When southwest winds blow along the coast of New Jersey for several
days in a row during the summer, the surface water does not move in
exactly the same direction as the wind. As the wind is blowing, the
earth is also spinning beneath the wind, which causes friction on the
surface water and pulls it in a different direction. This friction causes
the surface water to move at a right angle (90 degrees) from the direction
of the wind. If the wind is blowing from the southwest along the New
Jersey coast, and the water is moving 90 degrees to the right, then
the water is actually moving towards the southeast, or away from the
coast.
Confused?...don't be. Just remember that the surface water moves away
from the coast, even though the wind is blowing along (parallel to)
the coast. When the warm surface water moves away from the coast of
New Jersey in the summer, colder water from the bottom rises to replace
it along the shore, and an upwelling occurs.
Third Stage: Cold water brings nutrients to the surface.
Upwelling can have important impacts on the plants and animals in the
ocean. Phytoplankton are single-celled microscopic plants that live
in the ocean. Similar to plants on land, phytoplankton need light, nutrients,
and carbon dioxide to live and grow. Near the surface of the ocean,
there is plenty of light and carbon dioxide in the water, but usually
low levels of nutrients because they have been used up by the existing
phytoplankton. The cold water found closer to the bottom of the ocean
is rich in nutrients, and when these nutrients are carried to the surface
during an upwelling the phytoplankton can grow and multiply in huge
numbers. This is called a phytoplankton bloom. A bloom causes the water
to appear green and murky, and attracts fish and other marine creatures
who feed on the phytoplankton or the small animals that eat the phytoplankton. |
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