| Summary: | I Encuentro de la Oceanografía Física Española (EOF), 13-15 de octubre 2010, Barcelona We study surface chlorophyll concentration (CHL) variability in the eastern subtropical and tropical North Atlantic, using 49 years of reanalysis‐forced ocean model output. After establishing the model's skill by comparing the output with satellite‐borne CHL, we assess the mechanisms driving CHL variability in the model during the last half of the twentieth century. We find that two processes are primarily responsible for bringing nutrients to the euphotic layer and sustaining a chlorophyll response. One is coastal upwelling, determined by the alongshore component of the wind stress. It occurs in a narrow meridional band along the coast but further influences the offshore domain through horizontal Ekman transport and convergence of the meridional flow. Offshore upwelling, driven by wind‐stress curl provides the second nutrienty source. The northern offshore part of the study region, occupied by the subtropical gyre, is characterised by downward curl‐driven velocities. However, the southern part of the study region is characterized by cyclonic wind stress curl and thus Ekman suction. We find that variability in the boundary between the upwelling and downwelling domains, perhaps brought about by variability in large‐scale climate modes, is critically important in setting the offshore extension of the high chlorophyll region in the eastern subtropical and tropical North Atlantic Peer Reviewed
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