Documentation and Analysis of a Global CO2 Model Developed by Peng et al.
(July 1990)

H. I. Jager, T.-H. Peng, A. W. King, and M. J. Sale, Oak Ridge National Laboratory

In 1983, Peng et al. developed a modification of the Oeschger et al. 1975 ocean model. Both the original and the modification are one-dimensional representations of the ocean, including (1) CO2 exchange between a well mixed atmosphere and a well mixed ocean surface layer and (2) diffusive mixing into the waters lying below the mixed layer. Peng et al. also added a representation of deep-water cycling from intermediate depths to the surface polar outcrop to the ocean bottom and then back to the surface. In addition, they incorporated oceanic primary productivity into the model and benchmarked the model against the penetration of bomb-produced tritium measured by the Geochemical Ocean Sections Study (GEOSECS) program.

This report documents that modified model and describes how the model was standardized to allow comparison with other models. Before being subjected to sensitivity analysis, the standardized version of the model was supplemented with a calibration routine to define reasonable combinations of initial conditions. This routine improved the model's ability to hold an initial equilibrium state. The subsequent sensitivity analysis showed that the model was sensitive to different parameters at different points in its run time. For short runs, the initial conditions selected were of greatest importance; the significance of the initial conditions declined in longer simulations. With the pCO2 excluded from the sensitivity analysis, ocean surface area was always second in importance. Next, the CO2 exchange rate was most important in short runs, but the alkalinity of the oceans was in all but the shortest runs.

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