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.

The organic carbon fluxes mediated by planktonic communities in two cyclonic eddies (CEs) and two anticyclonic eddies (AEs) at the Canary Eddy Corridor were studied and compared with the dynamics in two far-field (FF) stations located outside the eddies. We observed favorable conditions and signs for upwelling at the center of CEs and for downwelling and mixing at the centers of AEs. CEs were characterized by a higher concentration of nutrients and the highest concentration of chlorophyll a (chl a), associated with the highest abundance of microphytoplankton and diatoms. AEs displayed concentrations of chl a values and nutrients similar to those at the FF stations, except for the highest ammonium concentration occurring at AE and a very low concentration of phosphorus at FF stations. AEs were transient systems characterized by an increasing abundance of picophytoplankton and heterotrophic bacteria. While primary production was similar between the systems, the production of dissolved organic carbon (P_DOC) was significantly higher in the AEs. Phytoplankton cell mortality was lowest in the CEs, and we found higher cell mortality rates at AE than at FF stations, despite similar chl a concentration. Environmental changes in the AEs have been significantly prejudicial to phytoplankton as indicated by higher phytoplankton cell mortality (60% of diatoms cells were dead) and higher cell lysis rates. The adverse conditions for phytoplankton associated with the early-stage anticyclonic systems, mainly triggered by active downwelling, resulted in higher cell mortality, forcing photosynthesized carbon to fuel the dissolved pool

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The carbon fluxes mediated by planktonic communities in two cyclonic eddies (CEs) and two anticyclonic eddies (AEs) at the Canary Eddy Corridor were studied and compared with the dynamics in two far-field (FF) stations located outside the eddies. We observed favorable conditions and signs for upwelling at the center of CEs and for downwelling and mixing at the centers of AEs. CEs were characterized by higher nutrients concentration and highest chlorophyll <i>a</i> concentration, associated with highest microphytoplankton and diatoms abundance. AEs displayed similar chlorophyll <i>a</i> values and nutrients concentration (except highest ammonium concentration) to those of the FF stations and were characterized by increasing abundance of picophytoplankton and heterotrophic bacteria. While primary production was similar between the systems, the production of dissolved organic carbon (P_DOC) was significantly higher at AEs. Phytoplankton cell mortality was lowest in CEs and we found higher cell mortality in AE than FF, despite similar chl <i>a</i> concentration. Environmental changes at the AEs presented significant prejudicial effects on the phytoplankton health as indicated by higher phytoplankton mortality (e.g. 60% of dead diatoms cells) and higher cell lysis rates observed at AEs than at two other systems. The adverse conditions associated to the early-stage anticyclonic systems, mainly triggered by active downwelling, resulted in higher consequent P_DOC production, corresponding to forcing of the carbon flux to the dissolved pool and a weakness of the carbon pump