Physical description of an upwelling filament west of Cape St. Vincent in late October 2004

Abstract

[1] The present paper describes the physical characteristics of an upwelling filament off Cape St. Vincent (southern Iberia) in October 2004, based on remote sensing, hydrographic, ADCP and wind data. It was associated with a meandering jet similar to eastern Pacific or Canary filaments, though its dynamical features were weaker as a result of the surface-trapped (top 100 m) and weak horizontal density gradients. The filament transported 0.9 Sv of coastal water offshore, of which 8% was due to Ekman transport; it formed following the destabilization of an alongshore equatorward upwelling jet close to the cape. The filament was structurally asymmetric, with anticyclonic geostrophic vorticity to the north and more strongly cyclonic to the south, as a result of the meanders and existing eddies. The filament comprised a sequence of cold, submesoscale ($30 km diameter) cyclones. Vertical velocities of ±15 mÁd À1 were associated with meanders of the jet. The surface and subsurface circulation was coupled. At middepths (90-150 m) anticyclonic recirculation of northern water seemed associated with a separated, older upwelling jet. Mediterranean Water (MW) was present below 350 dbar as a topographically steered undercurrent and a meddy-cyclone dipole. These undercurrents contributed to the formation of the October filament through baroclinic instability associated with the enhanced vertical shear.

Importance of the mesoscale in the decadal changes observed in the northern Canary upwelling system

“…39°N) show a weak warming trend when compared with the offshore waters, pointing out an enhancement of the thermal contrast at the upwelling front and the intensification of the equatorward upwelling jet that turns cyclonic into the Gulf of Cadiz at the discontinuity imposed by the Cape São Vicente. A signal of weaker warming trend is also seen associated to the upwelling filament recurrently observed at the Cape São Vicente and stretching west into the open ocean [ Sánchez et al , 2008]. Off the northern margin of the Gulf of Cadiz, west of Cape Santa Maria, the zone corresponding to the inshore warm countercurrent that develops towards the Cape São Vicente [ Relvas and Barton , 2005] shows a stronger warming trend, an indication of an increasing contrast with the upwelled water intruded from the west coast.…”

Primary productivity variability on the Atlantic Iberian Margin over the last 70,000 years: Evidence from coccolithophores and fossil organic compounds

“…In late spring through summer, the Azores High strengthens while the axis of maximum moisture transport and the predominant storm track extend to the north and east (Figure 1a). This results in decreased precipitation over southern Europe and northwestern Africa [ Trouet et al , 2009], attracting strong trades which produce coastal upwelling up to 200 km from the shore while enhancing the availability of nutrients and phytoplankton biomass accumulation in the western Iberian Margin [ Alvarez et al , 2005; Fiúza , 1983; Moita , 2001, Moita et al , 2003; Sánchez et al , 2007, 2008]. The water upwelled to the surface originates from either subpolar (>45°N, recently upwelled, cold, nutrient‐rich, and fresh) or subtropical (<45°N, warmer, nutrient‐poor, less ventilated, and saltier) branches of the eastern North Atlantic Central Water, subsurface components of the PC system, and the IPC [ Álvarez‐Salgado et al , 2003; Pérez et al , 2001; Rios et al , 1992].…”

“…The water upwelled to the surface originates from either subpolar (>45°N, recently upwelled, cold, nutrient‐rich, and fresh) or subtropical (<45°N, warmer, nutrient‐poor, less ventilated, and saltier) branches of the eastern North Atlantic Central Water, subsurface components of the PC system, and the IPC [ Álvarez‐Salgado et al , 2003; Pérez et al , 2001; Rios et al , 1992]. In late autumn through winter, the Azores High is weak and offers protection from northwesterly winds, making them weaker, while a northward IPC develops and downwelling occurs (Figure 1b) [ Relvas et al , 2007; Sánchez et al , 2008]. Additionally, although the phytoplankton biomass during summer upwelling has been quantified as at least 1 order of magnitude greater than in winter, upwelling also occurs during autumn or winter under northerly winds blowing at the shelf [ deCastro et al , 2008; Relvas et al , 2007].…”

Influence of a deep flow on a surface boundary current

“…The filaments carry nutrient-rich waters, and biological species, near the surface, from the coast into the oligotrophic ocean (Relvas et al 2007, Sanchez et al 2008. The eddies carry heat and salt from the undercurrents into the subtropical gyre of the North Atlantic Ocean, at intermediate depths (Iorga and Lozier 1999a, b, Serra and Ambar 2002, Che´rubin et al 2007, Carton et al 2010.…”