Significance of cyclonic SubTropical Oceanic Rings of Magnitude (STORM) eddies for the carbon budget of the euphotic layer in the subtropical northeast Atlantic

Abstract

The interannual and seasonal variability of cyclonic eddies budded from the Azores Current during the period 1993–1999 in the northeast subtropical Atlantic region (20°N–34°N; 19°W–35°W) was studied by using TOPEX/Poseidon and ERS-1/2 altimeter images, the operational ocean mesoscale forecasting system SOPRANE, and a mesoscale eddies automatic detection system. Seventeen cyclonic eddies were detected and monitored for time periods ranging from 50 to 360 days. They were characterized by mean westward velocity, amplitude, diameter, and eccentricity of about 2 km d−1, 8 cm, 187 km and 0.7, respectively. The generation of cyclonic eddies was subjected to an important interannual variability, especially in 1995 when the activity of cyclonic eddies in the northeast Atlantic was more intense and associated with parallel changes in the eddy energy of the Azores Current. Seventy-five percent of the mesoscale features were generated throughout the October–February period. Significant relationships were found between the seasonal NAO index and both the annual eddy kinetic and potential energy in the Azores Current region and also the total annual area occupied by STORM eddies, calculated with a 1-year phase lag. The outcome of this study was used to estimate the contribution of STORM eddies to the organic carbon deficit measured in the northeast subtropical Atlantic. On average, these eddies accounted for <1% of the net community production in the region.