At-Home STEM Activities: Ocean Currents

Dreaming of summer trips to the beach? This week we’re exploring different aspects of aquatic systems. 

Our oceans provide food, fun, beautiful views- and they’re also a huge part of climate and weather conditions as ocean currents move both water and energy from place to place. Exploring the weather is a topic for another week, but today we’ll look at the factors that help create and direct currents.  

Ocean current diagram courtesy of NOAA

Global ocean currents are driven by differences in water densities, while the movement of currents locally can also be influenced by the wind and the shape of the ocean floor. In this activity we’re going to demonstrate how water density, wind, and obstacles create the currents we see today.  

For this activity you will need: 

-a tall clear container for water 

-a wide container for water (could be the same as the above) 

-water 

-salt 

-food coloring 

-ground pepper 

-an ice cube tray 

-a way to heat up water 

-a spoon or stick for stirring 

-small objects that sink in water and can be placed in the containers 

1.Make colored ice cubes by freezing water colored with food coloring. (add enough coloring that the color is intense- this will make the demonstration easier to see) 

You can see the trails of darker cold water sinking down from the ice cube

2.Once the ice cubes are frozen, add room temperature or slightly warm water to the tall clear container, then place several ice cubes in the container. Notice what happens as the ice cubes start to melt- this is because cold water is denser than warm water, so the water from the ice cubes is sinking down. In the Northern Atlantic Ocean, water sinks as it cools , pushing the water below it out of the way in the form of a current that moves away from the pole. In areas of the Indian and Pacific Oceans, sunlight heats surface water and pulls colder water up from the depths.

3.But temperature is only part of the process. Now empty the tall clear container and refill it with hot water. Add salt and stir until the salt dissolves. Add several ice cubes to the container- did the same thing happen this time? Salt water is more dense than fresh water, so, if the hot water is salty enough, the colder water from the ice cubes will not sink (you can experiment with different amounts of salt to see how much is needed). The different temperatures and salinities of water in different parts of the oceans create the currents that move water around the globe- we call this thermohaline (temperature-salt) circulation. 

4.Other factors influence the shape and direction of currents. Wind is one of those factors. Fill the wide container with water and then sprinkle ground pepper on the surface- blow across the surface and notice how the pepper moves.  

The pepper followed currents around and away from objects- you’ll notice an area of clear water in the upper right

5.Put one of objects in the water and then blow across it again- how did the movement of the pepper change? Both above- and below-water obstacles channel moving water and shape the currents that encounter them. You can experiment with different combos of obstacles to see how the patterns change.  

Take it further:

-Try adding different amounts of salt to the warm water and then calculate the percent salt needed in the solution to keep the cold water from sinking

-use food coloring to color warm water and see if you can carefully pour it onto clear ice water so that it stays in a layer on the surface- the border between the two layers will have a rapidly changing temperature gradient or thermocline

-stir clear water in a container so that it is moving against sides and around obstacles- then add a drop of food coloring and notice how the dye moves