The amount of carbon dioxide removed from the atmosphere and stored in the oceans depends, in part, on the depth to which marine organic carbon sinks, according to a study published online in Nature Geoscience.
Marine organisms such as phytoplankton take up CO2 from the surface of the ocean as they grow. When they die, the phytoplankton sink and carry the organic carbon with them to deeper waters, where it is then remineralized back into CO2.
Using a global ocean biogeochemistry model, Eun Young Kwon and colleagues show that as the remineralization depth at which organic carbon is converted back to CO2 increases, the amount of CO2 injected into the bottom waters also increases. The net result is a reduction in the amount of CO2 escaping back to the atmosphere, and a decrease in the concentration of atmospheric CO2.
The remineralization depth is influenced by a host of climate-sensitive factors ― such as temperature, oxygen concentration and community composition ― and could therefore change as the planet warms, with important consequences for atmospheric CO2 concentrations.