The role of eddies in the isopycnic transfer of nutrients and their impacton biological production

Eddies provide a systematic, large-scale transfer of tracers and nutrients along isopycnals through a combination of eddy-induced diffusion and advect ion. The nutrient distribution is controlled by advection, rather than diff usion, when the nutrient lifetime exceeds a timescale given by kappa /V-2 w here kappa is the lateral diffusivity and V is the characteristic transport velocity. Idealized, eddy-resolving experiments are conducted using an iso pycnic model configured for a zonal channel. Whether the eddies act to enha nce or inhibit biological production depends on the location of the nutrien t source and the nutrient lifetime. For a subtropical gyre and the Southern Ocean, the eddy-induced diffusion and advection are likely to oppose each other over the euphotic zone but reinforce each other at depth. Over the eu photic zone, the combination of eddy diffusion and Ekman advection of nutri ents should dominate the opposing eddy-induced advection. This lateral tran sfer becomes more important for long-lived nutrients, such as dissolved org anic nitrogen, within the euphotic zone.