A poleward flow along the Atlantic coast of the Iberian peninsula

Abstract

Satellite Advanced Very High Resolution Radiometer (AVHRR) imagery and Argos tracked drifters have revealed the existence of a narrow, warm surface poleward current along the Iberian coast during autumn and winter. Six near‐surface drifter tracks indicated a net northward flow between September 1986 and March 1987, although individual drifter trajectories also provided evidence of eddy activity and episodes of equatorward flow. A SeaSoar survey during September 1986 in the region 37°–43°N, 9°–11°W showed that poleward flow at that time was associated with the northward advance of a warm, salty tongue of water throughout the upper 400 m layer. Infra‐red imagery confirmed the northward penetration of the warm current and its progression around Cape Finisterre along the north coast of Spain during the course of the winter. A similar situation is indicated by satellite imagery during other years. Current meter data show that poleward flow occurred along the continental slope down to depths greater than 600 m. Conductivity, temperature, and depth (CTD) casts show the presence of Mediterranean Intermediate Water (MIW) at depths greater than 600 m. The MIW does not flow as a simple northward flowing jet along the continental slope off Iberia, but instead shows evidence of eddies within the flow. The poleward surface current is in the opposite sense to the general summer circulation of the region, when cool upwelled water is advected equatorward. It is postulated that the poleward flow is generated by thermohaline forcing when the southward trade winds, characteristic of the summer months, weaken or reverse. Intermittent poleward flow appears to be a common characteristic of the Eastern Boundary throughout the North Atlantic from West Africa to the Norwegian Sea.

A Review of Abrupt Climate Change Events in the Northeastern Atlantic Ocean (Iberian Margin): Latitudinal, Longitudinal, and Vertical Gradients

“…1a). The IPC, extending down to 400 m, transports warm and salt-rich waters of 154 subtropical origin [Frouin et al, 1990;Haynes and Barton, 1990] and can be traced into the Bay 155 of Biscay. The IPC's subsurface or undercurrent part conveys ENACW of subtropical (st) origin 156 poleward year-round.…”

Sensitivity to open boundary forcing in a fine-resolution model of the Iberian shelf-slope region

“…This current, (which is referred to later as the poleward current) has a width of O(25 km) and extends from the surface down to O(200 m). The existence of this feature has been confirmed by satellite imagery, in situ hydrographic measurements and Lagrangian drifters, (Frouin et al, 1990;Haynes and Barton, 1990). According to Frouin et al (1990) only about one fifth of the observed transport of this current can be accounted for by onshore Ekman convergence induced by southerly winds.…”

Seasonal cycle of plankton production in the Iberian margin based on a high resolution ocean model

“…October--November represent a transition in the ecosystem from the summer dominant upwelling situation to the autumn dominant downwelling situation (Álvarez-Salgado et al, 2003;Castro et al, 1997), driven by a shift in the wind regime from northerlies to southerlies. It also coincides with the onset of the relatively warm and saline IPC over the slope (Haynes and Barton, 1990). This shift is usually coincident with a phytoplankton autumn bloom in the coast (Álvarez-Salgado et al, 2003;Bode et al, 1996;Casas et al, 1997;Castro et al, 1997).…”

“…This fact is usually attributed to an efficient recycling (mineralization) of organic matter under periodic (1--3 weeks) wind stress--relaxation cycles (Álvarez-Salgado et al, 1993;Arístegui et al, 2009). The autumn (October--November) brings a shift to southerly winds, which favors downwelling conditions over the shelf (Álvarez-Salgado et al, 2003), coinciding with the onset of a warm and saline poleward current over the slope, the Iberian Poleward Current (IPC) (Haynes and Barton, 1990). This shift is usually coincident with a phytoplankton autumn bloom in the coast (Álvarez-Salgado et al, 2003;Bode et al, 1996;Casas et al, 1997;Castro et al, 1997).…”