INFLUENCE OF MESOSCALE EDDIES ON NEW PRODUCTION IN THE SARGASSO SEA

It is problematic that geochemical estimates of new production-that fr action of total primary production in surface waters fuelled by extern ally supplied nutrients-in oligotrophic waters of the open ocean surpa ss that which can be sustained by the traditionally accepted mechanism s of nutrient supply.(1,2) In the case of the Sargasso Sea, for exampl e, these mechanisms account for less than half of the annual nutrient requirement indicated by new production estimates based on three indep endent transient-tracer techniques(2-6). Specifically, approximately o ne-quarter to one-third of the annual nutrient requirement can be supp lied by entrainment into the mixed layer during wintertime convection( 7), with minor contributions from mixing in the thermocline(8,9) and w ind-driven transport(10) (the potentially important role of nitrogen f ixation(11)-for which estimates vary by an order of magnitude in this region(12)-is excluded from this budget). Here we present four lines o f evidence-eddy-resolving model simulations, high-resolution observati ons from moored instrumentation, shipboard surveys and satellite data- which suggest that the vertical flux of nutrients induced by the dynam ics of mesoscale eddies is sufficient to balance the nutrient budget i n the Sargasso Sea.