Variations in the global carbon cycle during the Cretaceous related to climate, volcanism, and changes in atmospheric CO₂.

A marked increase in the rate of CO₂ outgassing due to volcanic activity between about 110 and 70Ma may have resulted in a buildup of atmospheric CO₂. A significant fraction of this atmospheric CO₂ may have been reduced by an increase in the production and burial of terrestrial organic carbon. Some excess CO₂ may have been consumed by marine algal photosynthesis, but marine productivity apparently was low during the Aptian-Albian relative to terrestrial productivity. Terrestrial productivity also may have been stimulated by increased rainfall that resulted from a warm global climate and increased marine transgression as well as by the higher CO₂. -Authors