Water Cycle - Oceans (6)
Post Lab 

   
OBJECTIVES:
  • Comparing the different reasons for ocean movements. 
  • Simplifying a map with complicated data.
VOCABULARY:
  • Coriolis
  • currents
MATERIALS:

Students use a worksheet to look at ocean currents.

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:
  1. 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. 
      
  2. 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.  
      
  3. 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. 
      
  4. 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.  
      
  5. 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. 

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