Recirculation of the Canary current in fall 2014

Abstract

Hydrographic measurements together with Ship mounted Acoustic Doppler Current Profilers and Lowered Acoustic Doppler Current Profilers (LADCP) obtained in October 2014 are used to describe water masses, geostrophic circulation and mass transport of the Canary Current System, as the Eastern Boundary of the North Atlantic Subtropical Gyre. Geostrophic velocities are adjusted to velocities from LADCP data to estimate an initial velocity at the reference layer. The adjustment results in a northward circulation at the thermocline layers over the African slope from an initial convergent flow. Final reference velocities and consequently absolute circulation are estimated from an inverse box model applied to an ocean divided into 13 neutral density layers. This allows us to evaluate mass fluxes consistent with the thermal wind equation and mass conservation. Ekman transport is estimated from the wind data derived from the Weather Research and Forecasting model. Ekman transport is added to the first layer and adjusted with the inverse model. The Canary Current located west of Lanzarote Island transports to the south a mass of 1.5 +/- 0.7 sv (1 sv = 10(6) m(3) s(-1) Re, 109 kg s-1) of North Atlantic Central Water at the surface and thermocline layers (similar to 0-700 m). In fall 2014, hydrographic data shows that the Canary Current in the thermocline (below at about 80 m depth to similar to 700 m) recirculates to the north over the African slope and flows through the Lanzarote Passage. At intermediate layers (similar to 700-1400 m), the Intermediate Poleward Undercurrent transports northward a relatively fresh Antarctic Intermediate Water in the range of 0.8 +/- 0.4 Sv through the Lanzarote Passage and west of Lanzarote Island beneath the recirculation of the Canary Current.