Coupling between the open ocean and the coastal upwelling region off northwest Africa: Water recirculation and offshore pumping of organic matter

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.