THE INFLUENCE OF THE SEASONAL MIXED-LAYER ON OCEANIC UPTAKE OF CFCS

The issue of the appropriate CFC boundary condition for the interior of the ocean is addressed. A review of observations clearly shows substantial departure from saturation equilibrium and represents the greatest uncertainty in interpreting CFC measurements. A series of simple models is developed to determine the factors: which control the CFC-11, CFC-12 and CFC-113 saturations and CFC-113:CFC-12 ratio age. The physical processes of subduction and entrainment have a strong effect; the sequestration of fluid in the seasonal thermocline and spatial variations in the depth of mixing are most important. The uncertainty in the chemical mechanisms has a smaller influence. To the limited extent that the observational database can be compared to the model results, there is good agreement. The model suggests that the variation in CFC-113:CFC-12 age is significantly less than in the saturations of CFCs 11, 12, or 113. However, given a physically realistic seasonal ocean model, the CFC saturation and age boundary condition should be predictable.