Ocean Current Activity

Introduction

Demonstrate the effects of temperature and salinity on the circulation of water and visualize ocean currents using this easy-to-set-up Ocean Current Activity Model.

Concepts

• Ocean currents
• Density
• Water temperature
• Salinity

Background

Ocean currents are continuously on the move. How they move influences the climate and living conditions for plants and animals in the ocean and on land. Surface currents generally affect the uppermost few hundred meters of the ocean. Most surface currents are caused by the wind—the friction between the air and water surfaces causes the water to move.

Ocean currents are either classified as warm-water or cold-water currents depending on their points of origination. For example, the current that flows along the west coast of the United States originates from cooler northern latitudes and is therefore known as a cold-water current. Conversely, the Gulf Stream Current that flows along the east coast of the United States originates near the equator and is a much warmer current. See Figure 1. Ocean currents flow in a clockwise direction in the Northern Hemisphere and a counter-clockwise direction in the Southern Hemisphere due to the Coriolis effect. The Coriolis effect is caused by the shifting of winds and surface currents due to the Earth’s rotation.

Deep in the ocean, water currents do not move because of the wind but rather due to density differences. Deep ocean currents occur when a portion of seawater becomes more dense than the surrounding seawater. Water becomes more dense if its salinity increases and/or its temperature decreases. Seawater of high density sinks below less dense seawater due to gravity. Seawater located near the North and South pole regions is very dense. As ice forms in these frigid areas, the seawater freezes and the excess salt is left behind in the unfrozen surrounding waters, which in turn increases the density of the water. Dense water from the pole regions sinks to the ocean floor and flows towards the equator. At the same time, less dense surface water at the equator flows toward the poles along the ocean surface creating a continuous ocean water cycle. Cold deep-water currents travel much slower than surface currents. In fact, it takes the water in deep ocean currents as long as 1000 years to move from a pole region to the equator!

In some areas, deep ocean currents rise to the surface of the ocean causing what is known as an upwelling. Upwellings occur where strong winds rapidly carry surface currents away from an area. Upwellings bring large amounts of nutrients from the bottom of the ocean toward the surface. The increased nutrient levels support areas of abundant ocean life and lead to excellent fishing grounds.

Experiment Overview

The purpose of this activity is to build a model for observing the origin and movement of ocean currents due to temperature and density differences.

Materials

Safety Precautions

Wear safety glasses or goggles whenever working with chemicals, heat or glassware in the lab; also chemical-resistant gloves and a chemical-resistant apron. Use heat-resistant gloves to handle the beaker of boiling water. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The materials used in this activity may be disposed of according to Flinn Suggested Disposal Methods #26a and #26b. The Ocean Current Activity Model should be cleaned and dried for future use.

Prelab Preparation

1. Obtain the two bottles with drilled holes, the two acrylic tubes, the stick of clay and the packet of petroleum jelly.
2. Place a layer of petroleum jelly around the outside edges of the ends of the acrylic tubes (see Figure 2). Smear the petroleum jelly so it is evenly dispersed around the outside edges of the tubes.
   {12789_Preparation_Figure_2_Acrylic tubes with petroleum jelly around outside ends}
3. Insert the ends of the tubes into the holes of the bottles. The tubes should extend into the bottles approximately ¼" (see Figure 3). Spread excess petroleum jelly around the outside of each tube where it enters the bottle to ensure a good seal is formed. 
   {12789_Preparation_Figure_3_Tubes inserted into the bottles}
4. For added leak-proof protection, break off a small piece of clay and roll the clay into a log-shaped piece. Wrap clay around the outside edges of each tube (see Figure 4).
   {12789_Preparation_Figure_4_Assembled ocean current activity model}

Preparation of Saltwater Solution for Part II

Prepare a saltwater solution for use in Part II by adding 70 g of sodium chloride to 250 mL of tap water. Add four drops of blue food coloring and mix well with a stirring rod.

Procedure

Part I. Effect of Temperature on the Circulation of Water

1. Slowly fill the bottles and the cross-section tubes with tap water until the level of the water in both bottles is just above the top tube (see Figure 5). Be sure that the cross tubes are completely filled with water. If any leaks are present, add additional petroleum jelly and/or reposition the clay barriers around the outside of the tubes.
   {12789_Procedure_Figure_5_Ocean current activity model partially filled with tap water}
2. Obtain a 250-mL borosilicate glass beaker. Using a hot plate or Bunsen burner, gently heat approximately 200 mL of water in a borosilicate glass beaker to near boiling.
3. Add four or five ice cubes to the bottle on the right side of the Ocean Activity Model.
4. Wearing heat-resistant gloves, remove the beaker of hot water from the heat source. Pour enough hot water into the left side of the Ocean Current Activity Model so that the water levels in the right and left bottles are equal.
5. Place four drops of blue food coloring into the cold water in the right bottle and four drops of red food coloring into the warm water in the left bottle. Use a stirring rod to stir the water in each bottle.
6. Have students make observations and answer the questions for Part I in the Ocean Current Activity Model Worksheet.
7. Empty the Ocean Current Activity Model after step 6 has been completed for use in Part II.

Part II. Salinity of Water

8. Obtain the empty Ocean Current Activity Model from Part I.
9. Slowly fill the bottles and the cross section tubes with tap water until the level of the water in both bottles is just above the top tube. See Figure 5 above. Be sure that the cross tubes are completely filled with water. If any leaks are present, add additional petroleum jelly and/or reposition the clay barrier.
10. Add the blue saltwater solution to the left bottle of the Ocean Current Activity Model until the bottle on the left is nearly full.
11. Have students make observations and answer the questions for Part II in the Ocean Current Activity Model Worksheet.
12. Empty the Ocean Current Activity Model and rinse well with tap water.

Student Worksheet PDF

12789_Student1.pdf

Teacher Tips

• This kit contains enough materials to perform the demonstration as written seven times.
• Ice cubes or crushed ice may be used in Part I of the experiment.
• Placing a white background behind the Ocean Current Activity Model for Part II will help students see the movement of the blue saltwater solution.
• After Parts I and II have been completed, rinse the Ocean Activity Model well with water. The model may be left assembled for future use if desired.
• Have students perform further research on actual ocean current locations and patterns.
• Discuss or have students perform actual density calculations (Density = Mass/Volume). Compare against the density of water.

Answers to Questions

Part I. Effects of Temperature on the Circulation of Water

1. Describe the movement of the red and blue liquids in the Ocean Current Activity Model.

   The red liquid (hot water) moved from one side of the model to the other side via the top tube. The red solution seemed to push the blue solution (cold water) downwards and moved the blue solution from one side of the model to the other side via the bottom tube. The blue solution slowly poured out of the bottom tube and began to fill the bottom of the side of the mode that originally contained the red solution.

2. What type of current does the red liquid represent?

   The red solution represents a warm surface current.

3. What type of current does the blue liquid represent?

   The blue solution represents a cold deep ocean current.

4. Given your observations, which is less dense—cold water or warm water?

   Warm water is less dense. The warm red water formed a layer over the cooler blue water.

5. Which type of ocean current—warm surface or deep cold water—moves more rapidly? Why?

   Surface currents move more rapidly than deep water currents due to their lower density and interaction with wind.

Part II. Salinity of Water

6. Describe the movement of the blue saltwater solution.

   The blue solution quickly sank to the bottom of the model and began to move from the original side of the model in which it was added to the other side of the model via the bottom tube.

7. Which solution is more dense—the blue saltwater solution or the colorless freshwater solution?

   The blue saltwater solution is more dense. This solution quickly sank to the bottom when it was added to this model.

8. List two ways ocean water may increase in density.

   Ocean water increases in density as the salinity concentration increases or as it becomes cooler.

9. What areas of the Earth contain ocean water of very high density? Why?

   The North and South Poles have ocean waters of very high density. As ice forms in these frigid areas, the seawater freezes and the salt is left behind in the unfrozen surrounding waters. The higher salt content increases the density of the water.

10. What is the rising to the surface of deep cold ocean currents called? Describe the benefits of this phenomenon.

    This is known as upwelling. Upwellings bring large amounts of nutrients from the bottom of the ocean towards the surface. The increased nutrient levels create areas of abundant ocean life which prove to be excellent fishing grounds.