Oceans & Carbon Dioxide (DP IB Geography)
Revision Note
Written by: Grace Bower
Reviewed by: Bridgette Barrett
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
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 Tips and Tricks
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
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