A nonlinear convolution model for the evasion of CO₂ injected into the deep ocean

Deep ocean storage of CO 2 captured from, for example, flue gases is being considered as a potential response option to global warming concerns. For storage to be effective, CO 2 injected into the deep ocean must remain sequestered from the atmosphere for a long time. However, a fraction of CO 2 injected into the deep ocean is expected to eventually evade into the atmosphere. This fraction is expected to depend on the time since injection, the location of injection, and the future atmospheric concentration of CO 2 . We approximate the evasion of injected CO 2 at specific locations using a nonlinear convolution model including explicitly the nonlinear response of CO 2 solubility to future CO 2 concentration and alkalinity and Green's functions for the transport of CO 2 from injection locations to the ocean surface as well as alkalinity response to seafloor CaCO 3 dissolution. Green's functions are calculated from the results of a three‐dimensional model for ocean carbon cycle for impulses of CO 2 either released to the atmosphere or injected a locations deep in the Pacific and Atlantic oceans. CO 2 transport in the three‐dimensional (3‐D) model is governed by offline tracer transport in the ocean interior, exchange of CO 2 with the atmosphere, and dissolution of ocean sediments. The convolution model is found to accurately approximate results of the 3‐D model in test cases including both deep‐ocean injection and sediment dissolution. The convolution model allows comparison of the CO 2 evasion delay achieved by deep ocean injection with notional scenarios for CO 2 stabilization and the time extent of the fossil fuel era.