Oceans & Carbon Dioxide (DP IB Geography)

Revision Note

Oceans as a Carbon Dioxide Store

  • Oceans contain large amounts of dissolved carbon 

  • They are carbon sinks or reservoirs for carbon storage 

  • Oceans capture and absorb carbon dioxide from the atmosphere:

    • This is the process of carbon sequestration 

  • Carbon moves from surface ocean layers to deeper ocean layers through:

    • Biological Carbon Pump

      • Tiny phytoplankton living in the upper layers need to photosynthesise. They absorb carbon dioxide during this process

      • Phytoplankton act as a source of food for other marine life. Carbon moves through the marine food chain into the different layers of the ocean

      • Species like plankton also sequester carbon dioxide and use it for their skeletons or shells

    • Carbonate Pump

      • After organisms die, skeletons or shells can dissolve into the water, enriching deep ocean currents with carbon 

      • Decaying organisms can also release carbon dioxide

      • As animals breathe, carbon is also released into oceans

      • Dead organisms can build up and eventually compress on the seafloor and turn into limestone sediment

    • Ocean Circulation (physical pump) increases the amount of carbon that can be stored in oceans:

      • Thermohaline circulation moves surface and deep ocean currents around the world in a cyclical pattern

      • Dissolved carbon moves around oceans through this circulation

      • Water density brings carbon-rich waters deep down into ocean stores in a process called downwelling

Diagram illustrating carbon cycling at a 'sere' (lithosere) level

Diagram explaining the carbon cycle in the ocean, showing the flow between atmospheric CO2, dissolved CO2, organic and inorganic carbon, and global carbon sinks.
Carbon cycling at a 'sere' (lithosere) level
  • Oceans are important for the future and for climate change, as they absorb vast amounts of carbon dioxide

  • However, warmer waters cannot absorb as much carbon dioxide as colder waters. As ocean temperatures rise, this could worsen climate change by reducing the efficiency of the oceans as a carbon sink

Oceans as a Source of Carbon Dioxide

  • Oceans are not only a store but also a source of carbon dioxide

  • The process of upwelling can bring carbon-rich waters to the surface; this carbon can then make its way back into the atmosphere

  • Disruption to the thermohaline circulation would cause large amounts of carbon to move upwards from deep ocean layers to the surface:

    • The ocean would become a greater source of carbon dioxide than a carbon sink 

    • This could be catastrophic for the climate 

  • As climate change worsens, oceans may become a larger source of carbon dioxide:

    • As sea ice melts, ocean waters can mix more freely, bringing up those carbon-rich waters from the depths of the ocean

    • Gasses are released more easily when ocean waters are warmer

Examiner Tip

There is much more evidence for oceans as a store of carbon dioxide, however, it’s really important to think about the future and climate change and the effects this could have on the ocean becoming a source of carbon dioxide!

Impacts of Ocean Acidification on Coral Reefs

  • As a result of burning fossil fuels, more carbon dioxide enters the atmosphere 

  • Oceans also absorb lots more carbon dioxide 

  • This increase in carbon dioxide increases the acidity of ocean waters 

  • This is the process of ocean acidification  

    • Coral reefs need to produce calcium carbonate to grow 

    • Each coral organism (polyp) secretes a skeleton of calcium carbonate; these form the reef

    • As the ocean acidifies, coral reefs struggle to produce this calcium carbonate

    • This means that coral reef skeletons cannot grow as quickly; they become much weaker and are more likely to break

  • Coral reefs are a vital food source and shelter for marine life

    • As coral reefs start to degrade, this threatens the marine wildlife that is dependent on coral reefs for survival

    • Coral reefs are also important for humans as they:

      • Are useful for protecting coastlines from erosion and storms

      • Are a hotspot for fishing industries 

      • Bring tourism to local areas

      • Produce extracts that are used in medicine

Image showing the process and effects of ocean acidification

Diagram showing how burning fossil fuels emit carbon dioxide, increasing ocean acidity which degrades coral reefs and affects coastlines, marine life, fishing, and tourism.
Image showing the process and effects of ocean acidification

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