The secondary ageostrophic circulation in the Iberian Poleward Current along the Cantabrian Sea (Bay of Biscay)

We present a diagnostic study of the secondary ageostrophic circulation associated with a meander of the Iberian Poleward Current (IPC). The study is undertaken from a hydrographic survey covering a small domain of the Cantabrian Sea, along the northern Spanish coast. The upper 250 m of the system consist of a wave-like eastward flow (the IPC) with maximum geostrophic velocities of 15 cm/s at surface. A deeper westward countercurrent (6 cm/s at 350 m) and an anticyclonic ring detached from the main zonal flow and extending through the whole water column are the other major constituents of the system. The vertical velocity field shows areas of ascent and descent motion that reach maximum absolute values of 8 m/day at about 200 m. Buoyancy advection and vorticity advection contribute almost equally to the observed ageostrophic vertical flow. The horizontal ageostrophic circulation (< 2 cm/s) is consistent with the divergence pattern observed at upper and lower levels. Intense salinity/temperature intrusions observed in different profiles are examined in the light of the diagnosed ageostrophic motion.