Search

Abstract: The surface and upper-thermocline waters of the Canary Basin are characterised by very strong coupling between the open ocean and the coastal upwelling region. Such coupling has its origin in water inflow into the upwelling region north of the Canary Islands and its recirculation south along the continental slope, which is the true Canary Current. A portion of this recirculating water is intermittently exported offshore through surface filaments. During late fall, a major diversion takes place at Cape Ghir, allowing the presence of northward flow from Cape Blanc till Cape Yubi. The fraction of water that flows through the Canary Archipelago is the origin of intense mesoscale variability south of the Canary Archipelago, which interacts strongly with the coastal region. These physical characteristics are responsible of intense alongshore and vertical fluxes of nutrients and dissolved inorganic carbon within the upwelling region. Coastal filaments and cyclonic eddies cause localised offshore export of nutrients and organic matter, making possible that respiration be several times larger than production in the open ocean. A major characteristic of the ecosystem comes from the seasonal variation in the current pattern, allowing coastal convergence and intense transfer of coastal properties to the open ocean during late fall. [Copyright &y& Elsevier]

• CVFZ and Cape Blanc filament interaction dictates meso-scale DOM and POM distributions. • DOM and suspended POM have a minor contribution to the oxygen demand of the CVFZ. • Mesopelagic respiration in the CVFZ is primarily supported by sinking POM. • Transport and biogeochemical processes in the CVFZ reshape water masses properties. The Cape Verde Frontal Zone (CVFZ) is a highly dynamic region located in the southern boundary of the Canary Current Eastern Boundary Upwelling Ecosystem. Due to the interaction of the Cape Verde Front with the Mauritanian coastal upwelling, the area features large vertical and horizontal export fluxes of organic matter. While the flux, composition and biogeochemical role of sinking organic matter have been thoroughly studied, much less attention has been paid to the dissolved (DOM) and suspended particulate (POM) organic matter fractions. Full-depth profiles of DOM and POM were recorded during an oceanographic cruise in the CVFZ, with four consecutive transects defining a box embracing the giant filament of Cape Blanc and the Cape Verde front. The distributions of DOM and POM and their C:N stoichiometric ratios in the epipelagic layer were strongly influenced by the position of the transects relative to the giant filament and the front. Geographical heterogeneity in POM and DOM distributions and elemental composition was also observed within each of the different water masses of contrasting origin present in the area (North and South Atlantic Central Water, Subpolar Mode Water, Mediterranean Water, Antarctic Intermediate Water, Labrador Sea Water and North East Atlantic Deep Water). These facts suggest that water masses properties are re-shaped by biogeochemical processes occurring within the CVFZ. Nevertheless, our analysis indicates that DOM and POM mineralisation represents only 8.1% of the inorganic carbon and 17.8% of the inorganic nitrogen produced by the local mineralisation of organic matter. Intense lateral export of POM and DOM out of the boundaries of the CVFZ is the likely reason behind these low contributions, which confirm the prominent role of sinking fluxes of organic matter for mineralisation processes in this region. The DOM distribution in the CVFZ interior is apparently affected by the dissolution of fast sinking particles. [ABSTRACT FROM AUTHOR]