The ocean carbon cycle

Lesson overview

This lesson introduces the Earth's Carbon Cycle, exploring how carbon moves between the atmosphere, living things, rocks, and oceans. The location and form of carbon in the environment greatly influence Earth's climate.

The lesson also discusses Blue Carbon, which is carbon stored in ocean and coastal environments, and its importance in regulating the climate. It explains that the current climate crisis is caused by excessive CO2 released by human activities, and suggests solutions involving reducing emissions and storing carbon in natural environments.

Learning outcomes
  • Understand the basics of the carbon cycle
  • Explore the connection between the carbon cycle, greenhouse effect, and climate change
  • Introduce the concept of blue carbon and its role in sequestering atmospheric carbon
  • Locate and understand the importance of major blue carbon habitats

This lesson requires students to have access to an atlas, detailed world map, or online map. Student groups will also need access to the materials listed in Activity Overview Build your own carbon cycle.

Lesson steps

1. Build your own carbon cycle (20 minutes)

Introduce the learning objectives using slide 2 and then move into the Activity Build your own carbon cycle. Detailed instructions are available in the Activity Overview. This activity can fronted by a quick whole class discussion to find out what students already know about carbon using slide 4.

Slides 5 to 10 contain background information on carbon stores and the carbon cycle. The diagram on slide 10 links to an interactive diagram that can help to consolidate student learning.

Debrief the activity using some or all of the following questions depending on the ability of your class.

  • What are the main components of the carbon cycle, and how do they interact with each other? Encourage students to identify the main components (atmosphere, living things, rocks, and ocean) and discuss how carbon moves between them.
  • How do plants and animals play different roles in the carbon cycle? Discuss the processes of photosynthesis (plants absorbing CO2) and respiration (animals and plants releasing CO2).
  • What human activities can affect the balance of the carbon cycle? Have students consider examples, such as burning fossil fuels, deforestation, and land use changes.
  • What happens to the carbon stored in rocks and fossil fuels when they are burned or exposed to the atmosphere? Explain how burning fossil fuels releases stored carbon back into the atmosphere, contributing to the greenhouse effect and climate change.
  • How do oceans and rocks act as carbon sinks? What might happen if these sinks become saturated or disrupted? Discuss the role of oceans and soil in storing carbon and the potential consequences of these sinks being unable to absorb more carbon or releasing stored carbon back into the atmosphere.
  • Can you think of any ways that we can help reduce the amount of carbon dioxide in the atmosphere? Encourage students to suggest ideas like planting trees, reducing fossil fuel use, or promoting renewable energy sources.
  • Why is it important to understand the carbon cycle and how human activities can affect it? Emphasise the connection between the carbon cycle, the greenhouse effect, and climate change, and the need for informed decision-making to mitigate negative impacts.

2. Carbon stores and flows (10 minutes)

Emphasise that some parts of the environment represent carbon stores; and it is possible to lock atmospheric carbon into these stores, a process called carbon ‘sequestration’. This can be achieved in non-living stores (the lithosphere) through e.g. sedimentation; and/or through incorporating carbon into living things (photosynthesising plants, the bodies of plants and animals). Explain that human activities can influence, and are in fact having a major impact on, the operation of the carbon cycle. Students should now add the information about the changes in the carbon stores since the Industrial Revolution (1750s) to their carbon cycle diagram.

Use slide 12 to display this information, and then check student understanding and surprise(?) using slide 14.

Slides 15 to 19 then link the changes in the Earth’s carbon stores and the changes in the carbon cycle to climate change, showing how carbon dioxide levels in the atmosphere have increased dramatically in past decades, with a knock-on rise in temperatures.

3. Blue Carbon habitats (15 minutes)

Blue carbon is a term used to describe the carbon that is captured and stored by the ocean and coastal ecosystems, such as mangroves, seagrasses, and salt marshes. Students might be familiar with the idea that human activities, like burning fossil fuels and deforestation, release carbon dioxide into the atmosphere. This atmospheric carbon is a major contributor to climate change and global warming.

However, what students might not know is that our ocean and coastal environments play a crucial role in reducing the impact of these greenhouse gases. Through a process called sequestration, these ecosystems absorb and store carbon from the atmosphere, effectively removing it from circulation.

Students can imagine the ocean and coastal habitats as natural sponges that soak up the excess carbon dioxide from the air. By doing so, they help to regulate the Earth's climate and mitigate the negative effects of human-induced carbon emissions.

Use slides 21 to 40 to introduce students to the ideas around blue carbon. Slides 21 to 30 relate learning back to the carbon cycle. Plants absorb carbon from the atmosphere and then can help to store it away for long periods in the soil and sediment. Slide 31 introduces the main blue carbon habitats. Slides 32 to 35 give a little more information on each of these and you can ask students whether they have seen or heard of any of these, even if only on TV. Slides 36 to 39 complete the exposition, sharing the two reasons why these blue carbon habitats are so great at absorbing carbon.

This lesson step is concluded using the Student Sheet Blue carbon sequestration to reinforce learning. Students can complete this independently or in pairs. Review the answers as a whole class plenary.

4. Blue Carbon Mapping (10 minutes)

Students will explore where blue carbon habitats are located, as well as the largest example of each of these habitats. Share this with students using slides 45 and 46, before setting the treasure hunt challenge using either the questions on slide 47 or using the Student Sheet Blue carbon mapping. Students will need an atlas or (online) map to complete this activity. Review the answers using slide 48. The answer to the final question 5 will depend on the location of the school.

5. Reflection and wrap-up (5 minutes)

Recap the main points of the lesson using the review pyramid on slide 49.

Home learning

Identify the blue carbon habitat closest to your school. Research and explain: a) The specific type of blue carbon habitat it is b) Its approximate size and location c) Two major threats it faces d) One conservation effort currently in place to protect it