Physical, Chemical and Biological Properties of the SubTropical Oceanic Rings of Magnitude (STORM) in the Eastern North Atlantic: Significance for the Carbon Budget of the Euphotic Layer

A SubTropical Oceanic Ring of Magnitude (STORM) that budded from the Azores Current was studied in the Eastern North Atlantic Ocean in April 1999. The cyclonic eddy, called Leticia, was centred at ~32.4{ ~}N - 28.7{ ~}W and extended across a scale of more than 200 km in an east-west direction. Shallowing (>50 m) of the deep chlorophyll maximum (>0.3 mg m-3) was observed at the eddy centre associated with vertical displacements of the isotherms (>100 m) within the photic layer. Integrated nitrate concentration over the photic layer was ~four-folds higher inside Leticia than at external region, however primary production rates were only slightly higher. Eddy diffusive fluxes across the nitracline explained less than 25% of the nitrate required to sustain the estimated new production. Intensive knowledge on the duration and intensity of the isopycnal doming above the euphotic layer and the residence time of the Storm eddies is needed in order to understand the significance of these mesoscale features upon the carbon and nitrogen budgets of the subtropical NE Atlantic. To this aim, a study of the interannual and seasonal variability in the generation of Storm eddies was carried out during the period 1993-1999 by using TOPEX-POSEIDON altimeter images and the operational ocean mesoscale forecasting system SOPRANE. The outcome of this study was used to quantify the contribution of Storm eddies to the photosynthetic production, as well as to the the respiration rate, of particulate organic carbon in the NE Atlantic Subtropical Gyre region (20-34{ ~} N; 19-35{ ~}W).