An observational study of oceanic eddy generation mechanisms by tall deep‐water islands (Gran Canaria)

Abstract

Oceanic eddy generation by tall deep‐water islands is common phenomenon. It is recognized that these eddies may have a significant impact on the marine system and related biogeochemical fluxes. Hence, it is important to establish favourable conditions for their generation. With this objective, we present an observational study on eddy generation mechanisms by tall deep‐water islands, using as a case study the island of Gran Canaria. Observations show that the main generation mechanism is topographic forcing, which leads to eddy generation when the incident oceanic flow is sufficiently intense. Wind shear at the island wake may acts only as an additional eddy‐generation trigger mechanism when the impinging oceanic flow is not sufficiently intense. For the case of the island of Gran Canaria we have observed a mean of ten generated cyclonic eddies per year. Eddies are more frequently generated in summer coinciding with intense Trade winds and Canary Current.

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

“…Previous studies described the vertical structure of both cyclones and anticyclones formed in the lee of the Canary Islands, mainly generated by the destabilization of the Canary Current by the island topographic forcing and by the wind-induced upwelling at the western coast of the island or downwelling at the eastern part [Pingree, 1996;Barton et al, 2000;Basterretxea et al, 2002;Piedeleu et al, 2009]. For a long time, the Canary Islands were considered as the dominating generation area in the CANUS .…”

Forcing of dissolved organic carbon release by phytoplankton by anticyclonic mesoscale eddies in the subtropical NE Atlantic Ocean

“…Indeed, our results documented the occurrence of anticyclonic wind curl/shear regions partly responsible for the eddies' generation (Jiménez et. al., 2008;Piedeleu et al, 2009) in the Canary Eddy Corridor, favoring downward Ekman pumping velocities (Jiménez et al, 2008) and downward fluxes (downwelling) as previously described (Basterretxea et al, 2002). Originally located at the vicinity of the productive Gran Canaria current, anticyclonic eddies sampled in this study were at their early stage characterized by particularly active downward processes, progressively depleting the system of nutrients and influencing biological processes at the upper layers.…”

“…The Canary Archipelago is a continuous source of mesoscale eddies generated by the Canary Current and of the trade wind perturbations by the islands' topography (Jiménez et al, 2008;Piedeleu et al, 2009) and the main pathway of long-lived eddies in the subtropical northeast Atlantic, originating at the Canary Eddy Corridor . Lasurveyed eddies have been located, may be viewed as tall deep islands due to their steep and higher topography.…”

Photophysiological variability and its influence on primary production in the NW Africa–Canary Islands coastal transition zone

“…The archipelago perturbs the flow of both the Canary Current and the Trade winds (Arístegui et al 1994;Barton et al, 1998;Sangrà et al, 2009), leading to the formation of eddies that are shed downstream from the islands. The perturbation of the Canary Current seems to be the main source for eddy generation, since eddies have been observed in the region even in winter, when wind intensity is very low (Arístegui et al, 1994;Rodríguez et al 1999;Piedeleu et al, 2009). Consequently, the region represents a continuous source of eddies that can remain as coherent structures for several months (Sangrà et al, 2005(Sangrà et al, , 2007 while they are propagated westward ).…”