Ocean carbon sink duration under stabilization of atmospheric CO 2 : A 1,000‐year timescale

Ocean CO 2 uptake, moderated by the slow mixing of dissolved inorganic carbon to the ocean depths, is estimated to have a duration of ∼1,000 years when the atmosphere is held at a constant “stabilized” CO 2 concentration. This timescale is found to be several times longer than the relaxation time for the atmosphere‐ocean system to come to equilibrium when forced by a CO 2 emission impulse. Furthermore, the 1,000 year timescale is found to be insensitive to atmospheric CO 2 concentration level. Beyond 2,000 years, sediment CaCO 3 neutralization becomes the dominant mechanism for CO 2 uptake further extending the timescale of the ocean carbon sink. The equilibration time of the atmosphere‐ocean system, on the other hand, is shown to lengthen with increasing magnitude of CO 2 emissions. Estimates are based on the response of a 3D‐ocean carbon cycle model, and this behavior explained using the analytic solution of a simple box model.