| Summary: | Memoria de tesis doctoral presentada por María Virtudes Pastor Molla para optar al grado de Doctora por la Universidad de Las Palmas de Gran Canaria (ULPGC), realizada bajo la dirección del Dr. Josep Lluís Pelegrí Llopart del Institut de Ciències del Mar (ICM-CSIC).-- 212 pages [EN] Coastal upwelling in the eastern margin and offshore curl-driven upwelling in the southeastern margin, make the subtropical Northeast Atlantic a region of major primary productivity. When examining a broad zonal area, from the coast to 40º W, we find that the upward transport of nutrients due to offshore curl-driven upwelling becomes the main control on productivity. Nevertheless, despite its relatively small zonal extension of about 100 km, coastal upwelling extends its impact towards the open ocean through offshore Ekman transport and convergence of the meridional flow at Cape Blanc (21º N). Analysis of hydrographic data from spring 1973 and fall 1975 shows an export from the coast to the open ocean of 2.9 Sv of water mass and 53 kmol s-1 of nitrate during spring and 0.6 Sv and 3 kmol nitrate s-1 during fall in the area south of Cape Blanc. It is fundamental to improve our understanding of the distribution of the different water masses of the upper thermocline, as they carry the nutrients that will reach the euphotic layer and sustain primary production. In the study region, central waters of northern and southern origin meet at the Cape Verde frontal zone. Northern waters are nutrient-poor and oxygen-rich while local southern waters are nutrient-rich and oxygen-poor. Here, intense double diffusive mixing enhances horizontal heat transfer, thus the front appears as a smooth feature in terms of temperature, but resembles a barrier in terms of other properties such as salt or nutrients. The application of an Optimum Multiparameter analysis to hydrographic data collected during November 2007 and November 2008 shows a sharp front separating the central waters of northern and southern origin. In contrast, at intermediate layers, the ...
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