The vertical structure of mesoscale eddies in the Azores Current corridor: a combined altimetry-ARGO analysis

Abstract. Temperature and salinity, derived from over 20000 Argo profiles, are combined with 20 years of eddy trajectories and absolute dynamic topography maps to characterise the vertical structure of mesoscale eddies within the Azores current corridor (AzCCo) from surface to 1500 dbar. The isopycnal decomposition temperature and salinity anomalies into two components – heave (HEV) (vertical deflection of isopycnal surfaces) and spice (SPI) (variation along an isopycnal surface) – are directly associated with two main eddy transport mechanisms: eddy pumping and eddy trapping. From east to west, our statistics reveal an intensification of the anomalies' maximum (from 0.5 °C and 0.1 to above 1.5 °C and 0.2 of salinity) and a deepening of their core location in the water column (from 250 dbar to 750 dbar) for both anticyclones and cyclones. Furthermore, the absolute values of isopycnal vertical displacement above 50 dbar, from the surface to the 1500 dbar level, demonstrate the significant impact of these mesoscale structures throughout the water column. Anticyclones are characterised by a more barotropic structure, exhibiting warm, salty cores, while cyclones demonstrate a more baroclinic structure, featuring cold, fresh cores along the AzCCo. The origins of the sampled eddies can explain the zonal differences in vertical structure on either side of the Mid-Atlantic Ridge (MAR). In the west, most eddies could originate from the Gulf Stream branches, resulting in higher anomaly values to the west of the MAR. The HEV process dominates the resulting vertical structures of temperature and salinity within the water column. SPI exhibits higher values within the upper 250 dbar to the east of the MAR, reflecting an eddy's tendency to trap different water masses at the surface. The dominance of HEV indicates that most eddy-induced anomalies originate from eddy pumping, which is manifested as deflections of isopycnal surfaces. This mechanism produces warmer, saltier anomalies within anticyclonic eddies due to downwelling of isopycnal surfaces and colder, fresher anomalies within cyclonic eddies due to upwelling of the same surfaces.