The Canary intermediate poleward undercurrent: not another poleward flow in an eastern upwelling boundary

Poleward undercurrents are well known features in Eastern Boundary upwelling systems. In the California Current Eastern Boundary upwelling system, the California poleward undercurrent has been widely reported (Collins et al. 2004; Collins et al., 1996; Collins et al., 2018; Garfield et al. 1999), and it has been demonstrated that it transports nutrients from the equator waters to the northern limit of the subtropical gyre. However, in the Canary Current Eastern Boundary upwelling system, the Canary intermediate poleward undercurrent (CiPU) has not been properly characterized, despite recent studies arguing that the dynamics of the eastern Atlantic play an important role in the Atlantic meridional overturning circulation, specifically on its seasonal cycle. We use trajectories of Argo floats and model simulations to characterize the CiPU, including its seasonal variability, and the driving mechanism. The Argo observations show that the CiPU flows from 26°N, near cape Bojador, to approximately 45°N, near cape Finisterre in the northwest Spanish coast. The CiPU flows deeper than the California undercurrent (CU), with a mean depth at around 800 m. The CiPU shows a marked seasonal variability, with its maximum strength in fall, and the minimum in spring, and is driven by the along pressure gradient force, which, contrary to what happens along other eastern boundaries, in the Canary Current Eastern Boundary upwelling system is still significant below 500 dbar.