On the relations among CFC derived water mass ages

In waters formed before similar to 1975, Chlorofluorocarbon (CFC)-12 ventil ation ages are usually older than CFC-11 ages? which are in turn older than CFC ratio ages. A simple model shows that these discrepancies result from the effects of mixing on CFC ages, which are biased due to the nonlinear in creases in atmospheric CFCs before 1975. CFC-11 ages are biased younger tha n CFC-12 ages because CFC-11's relative increase rate in the atmosphere was higher. In the model results, ideal ages are consistently older than CFC a ges in waters ventilated prior to similar to 1975. The differences between CFC ages and ideal ages are reflected ih the discrepancies among CFC-II, CF C-12, and CFC ratio ages, however, and increase with increasing importance of diffusive versus advective tracer transport. Thus it may prove possible to estimate the magnitude of CFC age mixing biases based on differences mea sured between CFC-11, CFC-12, and CFC ratio ages.