How much CO2 gas can sea water hold?

Grade Level: Secondary

National Science Education Standards

Physical Science: Interactions of energy and matter
Life Science: Matter, energy, and organization in living systems
Earth and Space Science: Geochemical cycles

After this activity, students should be able to:

1. Explain the relationship between water temperature and gas concentration.
2. Use a graph to describe how sea surface temperature changes with the seasons.
3. Hypothesize how changes in sea surface temperatures through the year might affect the amount of carbon dioxide in the ocean and atmosphere.
4. Test their hypotheses by graphing and analyzing BATS temperature and carbon dioxide data.

People burn fossil fuels like gas, oil, and coal to drive cars, generate electricity, and heat buildings. Burning these fuels puts additional carbon dioxide into Earth's atmosphere. During the last 200 years, people have raised the concentration of carbon dioxide gas (CO2) in the air from about 270 parts per million (ppm) to about 360 ppm.

CO2 and other gases in the atmosphere trap heat energy that would otherwise escape to space. This is called the greenhouse effect. Most people agree the greenhouse effect will increase the Earth's average global temperature. This is called global warming.

However, people disagree about how much the Earth will heat up, and whether temperatures will change the same amount everywhere. Some people even think that "global warming" will cause some parts of the Earth to cool down during certain seasons.

One of the reasons that people aren't sure about global warming is that we don't fully understand what happens to CO2 and other gases once they go up a chimney or out a car's exhaust pipe. One of the main questions is how much CO2 stays in the air, and how much dissolves into the ocean. If a lot of CO2 ends up in the ocean, there will be less in the air, and the effects of global warming may be reduced. If the ocean releases CO2 back to the atmosphere, the greenhouse effect may be enhanced or prolonged.

The temperature of water at the sea surface is one factor that affects how much carbon dioxide gas ocean water can hold. We can use BATS data to explore how sea-surface temperatures change through the seasons, and how those changes affect the concentration of CO2 in sea water and the atmosphere.


1. Introduce the relationship between water temperature and gas concentration by conducting the hands-on activity described below. This is best done in the context of a unit on the carbon cycle and/or global climate change.

2. Ask your students to plot a time series of the sea-surface temperature (i.e., upper 5 meters) for each month of the year at an open-ocean location such as the BATS site. Stress that the ocean covers 70% of the Earth's surface, so that seasonal changes in sea-surface temperatures affect the exchange of carbon dioxide gas between ocean and atmosphere on a global scale. Students can draw their time series plots using the OceanExplorer TimeSeries tool or graph paper.

3. Discuss the similarities and differences among the sea-surface temperature plots that your students have drawn.

4. Compare student time-series temperature plots against temperature data from BATS. Discuss the similarities and differences. You can use the BATS time-series plot shown below (Fig. 1), present the students with a plot that you've constructed using OceanExplorer, or let the students use OceanExplorer to create their own plots.


5. Based on what your students learned in the hands-on activity and from their temperature time-series plots, have them add to their temperature plot a time series of the CO2 content of surface sea water for each month of the year at an open-ocean location such as the BATS site. Predict and discuss during which month of the year the surface of the Sargasso Sea would soak up the most CO2 from the atmosphere. During which month would the Sargasso Sea soak up the least?

6. Now compare student temperature and CO2 plots with temperature and CO2 data from BATS. Discuss the similarities and differences. You can use the OceanExplorer temperature and CO2 time series plot shown below (Fig. 2), present the students with a plot that you've constructed using OceanExplorer, or let the students use OceanExplorer to create their own plot.


Hands-on Activity
This simple hands-on activity will help your students explore the relationship between water temperature and the amount of carbon dioxide gas the water can hold. Have your students cool a 1-liter plastic bottle of carbonated water by placing it in an ice bath or refrigerator. Have them warm another bottle of carbonated water in the sun. Wait until the bottles have cooled or warmed sufficiently, then retrieve them. While waiting, discuss how carbonated water differs from regular water, and have the students hypothesize about what will happen when they open the warmed and chilled bottles. Encourage them to discuss each other's hypotheses.

What controls how much carbon dioxide gas the ocean holds? Well, think of a can of soda pop. Just like the ocean, pop or other carbonated drinks contain dissolved carbon dioxide gas. And what happens when you open a pop can that has been sitting in the warm sun?— Phoooosssh!! Bubbles of carbon dioxide gas shoot out, spraying you with soda. When you open a chilled bottle, it bubbles little or not at all. So, the warmer a liquid, the less gas it can hold. The cooler a liquid, the more gas it can hold. The same is true for the ocean. If sea water heats up, it tends to release carbon dioxide. If sea water cools down, it tends to soak up carbon dioxide. Carbon dioxide levels in the ocean also depend on other things, like how acidic the water is. But for right now, let's focus on the effects of temperature.

2 one-liter plastic soda bottles filled with carbonated water
ice or refrigerator
OceanExplorer interactive worksheet


You can evaluate your students´ preconceptions about ocean temperature and CO2 concentration by examining  the graphs that they draw using the OceanExplorer TimeSeries tool. You can then compare graphs that they draw following the activities in this lesson plan to gauge how their understanding of ocean temperature and its effect on carbon dioxide concentrations has changed.


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