Sarmiento, J. L., M. J. R. Fasham, U. Siegenthaler, R. Najjar, and J. R. Toggweiler, 1989: Models of Chemical Cycling in the Oceans: Progress Report II, Ocean Tracers Laboratory Report #6, Princeton University, 46 pp.

Abstract: In a previous progress report (Toggweiler, et al., 1987) we argued that the most difficult obstacle that needed to be overcome in developing predictive, dynamical, 3-D models of geochemical cycling in the oceans was to develop approaches for simulating the role of biological processes. In this report we update our progress on developing an ecosystem-level description of upper ocean fluxes and on simulating the penetration of anthropogenic CO₂ into the ocean. if the natural carbon cycle and ocean circulation are in steady state, one needs to know only the pre-anthropogenic surface total carbon and alkalinity to predict the uptake of fossil CO₂ by the oceans. As a first simple approximation, we fix the surface alkalinity at a constant value of 2300 ueq kg^-1, and fix the pre-anthropogenic surface total carbon to the value that gives the pre-anthropogenic pCO₂ of 280 ppm everywhere. This neglects details of the natural cycles of CO₂ due to temperature as well as biology that give rise to non-equilibrium pre-anthropogenic pCO₂ levels over much of the ocean. Several fossil CO₂ uptake experiments have been performed with this approach, both with 3-D ocean circulation models and with a new box model that incorporates features not included in previous box models. Another approach we are working on is a determination of the pre-anthropogenic surface total carbon and alkalinity based on the observed surface nutrient distributions and an assumed Redfield stochiometry. This approach gives us the concentration of pre-anthropogenic total carbon and alkalinity that we need for the steady state simulations of fossil CO₂ uptake discussed above. It also provides a simple way of simulating the effects of biology and temperature in the euphotic region of the ocean, allowing us to put major emphasis on processes occurring below the euphotic zone. Our simulations of processes below the euphotic zone suggest an important role for substances not caught in sediment traps, such as dissolved organic matter. We have made considerable progress on the development of ecosystem models of the upper ocean and have performed a first experiment incorporating these models into a 3-D ocean circulation model of the North Atlantic. Such models are necessary for predicting how the atmospheric pCO₂ will be affected should the ocean circulation and biology begin to change in response to a greenhouse climate.