- Atmosphere to terrestrial biosphere: The terrestrial biosphere takes in carbon through photosynthesis. Photosynthesis is the process plants use to make their own food. They use carbon dioxide in the air and sunlight to form sugar. Plants take in 120 gigatons of carbon dioxide from the atmosphere per year as a result of photosynthesis.
- Terrestrial biosphere to atmosphere: All living things respirate. Respiration is the process by which organisms take in oxygen and produce carbon dioxide as waste. Humans and other vertebrate animals do this by breathing, breathing in oxygen and breathing out carbon dioxide. Plants do this too, although they don’t technically “breathe”. This can be a point of confusion for many people, as we generally think of plants taking in what we breathe out through photosynthesis. Plants do take in carbon dioxide, but they also release it through respiration.
Overall, plants take in much more carbon dioxide through photosynthesis than they release through respiration, which is why the exchange between the terrestrial biosphere and atmosphere is about even. Plants take in a lot of carbon but release a much smaller amount; animals and other life forms release the rest so that the amount taken by plants is about the same as that released by all life forms. - Atmosphere to ocean: Algae in the ocean takes in a significant portion of carbon dioxide through photosynthesis. Carbon dioxide also dissolves water. This means that whenever the air touches the water, some carbon dioxide gets dissolved. Waves stir up the water, causing it to interact with more air and dissolving more carbon dioxide. The total carbon taken up by algae and the water itself is about 90 gigatons.
- Ocean to atmosphere: Life in the ocean respirates, releasing carbon dioxide. Water at the bottom of the ocean is carbon-rich, because all the life in the ocean eventually dies and drifts to the bottom. When ocean processes bring this carbon-rich water closer to the surface, the warmer temperatures evaporate the water and release carbon back into the atmosphere.
The fast carbon cycle
The atmosphere, terrestrial biosphere and ocean exchange carbon constantly.