Transient tracers in a global OGCM: Source functions and simulated distributions

The global oceanic distributions of the transient tracers tritium, tritiogenic ³He, and the chlorofluorocarbon CFC-11 (CFCl₃) are modeled by using the velocity field of the Hamburg Large Scale Geostrophic (LSG) model. Source functions for these tracers are presented including the extension of the global tritium source function from 1975 to 1995. The tracer distributions are compared with observations. The sensitivity of the tritium and CFC-11 simulations to the variation of adjustable parameters in the source functions is determined. The adjustable source function parameters cannot be varied to simultaneously achieve both a proper reproduction of the overall tracer inventories and the observed patterns of the tracer distributions. Further improvements are only possible through a change in the velocity field itself. Therefore anthropogenic tracers indeed provide a firm reality check for model ocean velocity fields. The model is used to simulate the future evolution of transient tracer fields for different oceanic regions until the year 2050.