BACKGROUND:
The motion in the oceans is important
to help predict global weather matters. But how the oceans travels
is very complicated. Not only does the surface move, but there are
many different layers in the ocean that sometimes move in different direction.
Density and temperature can create water masses that move as a unit.
Within each water masses it can be full of nutrients to sustain biological
life or sometimes it is nutrient poor that cannot sustain biological life.
This can cause the food chain to be either prosperous or could have devastating
results.
Movement is very difficult to understand,
especially when children think that when they stop, there is no movement.
Wrong! Ask the children to think of themselves as Martians, looking
at the Earth through their spaceship. As they look at this blue planet
called Earth, they notice that polar bears and penguins look like they
are standing still (acting cool), but people especially those that live
near the equator are moving around very quickly, about 1000 miles per hour!
But do the people feel like they are moving that fast? Of course
not, but the Earth is moving along its axis, a particle near the axis moves
slower than a particle along the equator, which has a longer distance to
travel. Hence, the Martian would see polar bears (who
live only near the north pole) and penguins who live only near the
south pole) as moving very slowly. This movement causes motion on
the crust of the Earth, but because the ocean is a liquid it responds more
quickly than the solid Earth and is one of the main reasons we have currents.
The different relative movement on the Earth
causes what is called the Coriolis Motion. The Coriolis effect is
a major overlay on the pattern, and this has to do with deflection of particles
because of this motion. The classic example that you can perform
with your children is to have them throw a ball to a person when they are
on merry-go-round. The ball will be thrown straight, but will appear
to be deflected to the people on the merry-go round. This is an analog
to the movement of water in our oceans. In the northern hemisphere
this deflection is to the right and in the southern hemisphere this deflection
is to the left.
Coriolis does not alone explain movements,
but other factors not related to movement such as density of water, wind
and local submarine topography need to be included. The main idea
here to convey to your students is that oceans have water flowing within
the main body, kind of rivers within the oceans, flowing in the direction
that other factors as mentioned above control. If your students can
understand that water does move in the oceans, and that this movement can
bring water from one side of the ocean to another, they may be able to
visualize this warming of the east Pacific.
PROCEDURE:
- This exercise reinforces
the concept that the surface waters of the oceans move. Emphasize
that the oceans do not just "sit" still, but are moving all the time.
- Have the students label the continents
and oceans on the lab sheet. Notice that this map shows more of the
oceans. It may be difficult for students to find the continents, so having
a globe available would assist students in finding the different areas.
- Have students try to simplify the
surface currents on the blank map. Tell them to substitute a larger
arrow for several of the smaller ones. Although this is a tedious
process, it gets them learning about the ocean's movement. Make sure
the students do this in pencil, there will be lots of erasing.
- Someone in the class will probably
ask, "What makes the currents move?" At the elementary school level
you can answer simply that the movement of the Earth as it spins around
on its axis while orbiting the Sun creates movement. Added complications
to the currents include: A) wind B) differences water height (example:
the Atlantic Ocean is higher than the Pacific Ocean near the Panama Canal)
and c) topography. There are several other factors, but at this stage
of the educational game, don't worry about it.
- Students may want to know how tides
play a part. Tides are caused by the gravitational attraction of
the Moon and Sun. The attraction actually bulges the water, almost
like a pulse. Certain times of the month the attraction is greater
and some less. Tides however don't change the major direction of
the movement of oceans.
