The Eastern Subtropical Gyre (North Atlantic): Flow Rings Recirculations Structure and Subduction

Abstract

Thirteen carefully prepared drogued buoy assemblies have been deployed in the eastern subtropical North Atlantic giving ~20 buoy years of Lagrangian data at a depth of 200 m. The buoy results together with hydrography have revealed the structure of the eastward flowing Azores Current (AC). The main jet had a transport of 26 Sv (near 28°W) with compensating counterflows in March 1992. Jet and counterflows were readily seen in the ADCP current structure and evident in the upper layer temperature (salinity) structure on an isopycnal surface. Buoys and hydrography showed that the adjacent westward flowing counterflows resulted in recirculation both north (anticlockwise circulation) and south (clockwise circulation) of the AC - the Subtropical Recirculations. South-south-west flow (3 cm s−1) occurred in the central region of study west of the Canary Islands. The long-term movement measured in the south or northern North Equatorial Current region was 3·5 cm s−1west-south-west. The mean south displacement per year of the buoys was 2·2° of latitude to the south and most of this displacement occurred in the first half of the year (February-August). The maximum westward displacement rate occurred six months later in October and November. The Subtropical Front/Azores Current region was identified as a zone of increased levels of kinetic energy (>100 cm2s−2) at a latitude near 34°N at the 200 m level, stretching for >2000 km, and as a marked horizontal winter sea surface temperature contrast at a latitude near 36°N. Winter mixing created an outcropping region of water with density in the range 26–4<σ0<26·6 kg m−3along the Subtropical Front near 34°N with a maximum vertical extent of 200 m.