MODELING OCEAN CARBON-CYCLE WITH A NONLINEAR CONVOLUTION MODEL

A nonlinear convolution integral is developed to model the response of the ocean carbon sink to changes in the atmospheric concentration of CO2. This model can accurately represent the atmospheric response of c omplex ocean carbon cycle models in which the nonlinear behavior stems From the nonlinear dependence of CO2 solubility in seawater on CO2 pa rtial pressure, which is often represented by the buffer factor. The k ernel of the nonlinear convolution model can be constructed from a res ponse of such a complex model to an arbitrary change in CO2 emissions, along with the functional dependence of the buffer factor. Once the c onvolution kernel has been constructed, either analytically or from a model experiment, the convolution representation can be used to estima te responses of the ocean carbon sink to other changes in the atmosphe ric concentration of CO2. Thus the method can be used, e.g., to explor e alternative emissions scenarios for assessments of climate change. A derivation for the nonlinear convolution integral model is given, and the model is used to reproduce the response of two carbon cycle model s: a one-dimensional diffusive ocean model, and a three-dimensional oc ean-general-circulation tracer model.