Uptake of excess CO2 by an outcrop‐diffusion model of the ocean

A carbon cycle model is presented in which direct ventilation of intermediate and deep ocean waters in high latitudes is taken into account. The 1½‐dimensional ocean model is an extension of a box‐diffusion model including a deep‐sea outcrop at the surface. If both are calibrated in a consistent way, the outcrop‐diffusion ocean takes up more excess CO 2 than the box‐diffusion ocean because the outcropping deep water is essentially virgin as to fossil CO 2 . Two calibration methods are compared, using the distribution either of natural or of bomb‐produced 14 C. The latter leads to a higher oceanic uptake of excess CO 2 than the former and to a better agreement with the observed atmospheric increase. Long‐term model responses are also discussed.