ON MODELS OF BOMB C-14 IN THE NORTH-ATLANTIC

Coarse resolution general circulation ocean models show a tendency to accumulate an excess of bomb C-14 On the eastern margin of the subtrop ical gyres, while observations suggest an excess is found in the west. Here simulations of the bomb C-14 transient in the North Atlantic Oce an are made using coarse resolution (1.0 degrees X 1.2 degrees) and '' eddy-permitting'' (1/3 degrees x 2/5 degrees) tracer transport models. The former employs large horizontal diffusivities to parameterize edd y transfer. Both models employ the same air-sea exchange parameterizat ion, with a specified tropospheric history of Delta(14)C. The coarse r esolution model accumulates C-14 evenly over the whole subtropical gyr e, while the eddy-permitting model has a pronounced maximum column inv entory in the western part, consisent with the observed patterns. The prescence of explicit eddies enhances tile ventilation of density surf aces in the recirculation zone on the western margin of the gyre, sugg esting that the zonal gradient hinted at in the observations is intima tely tied to properties of geostrophic eddy dynamics which are not cap tured parametrically in the coarse resolution model.