3-DIMENSIONAL CIRCULATION OF A MESOSCALE EDDY FRONT SYSTEM AND ITS BIOLOGICAL IMPLICATIONS/

The three-dimensional circulation of an eddy/front system is quantifie d using hydrographic data collected in the Channel of Ibiza, Western M editerranean, during November 1990. The ageostrophic motion is derived from the quasi-geostrophic omega equation. Maximum upward velocities (approximate to 4 m/day) are diagnosed on the cold side of the front i n the vicinity of a cyclonic eddy and coincident with a sub-surface co nvergence (below 50 m). This upward motion can be explained in terms o f advection over isopycnals that uplift in the along-front direction. We also show the relevance of the three-dimensional circulation for th e enhanced fertilization observed in the surface layer. Our results es tablish the importance of the ageostrophic dynamics induced by frontal mesoscale events for the regional ecology of the Balearic Sea.