Spatial and temporal seasonal trends in coastal upwelling off Northwest Africa, 1981-2012

Seasonal coastal upwelling was analyzed along the NW African coastline (11-35 degrees N) from 1981 to 2012. Upwelling magnitudes are calculated by wind speed indices, sea-surface temperature indices and inferred from meteorological station, sea-surface height and vertical water column transport data. A permanent annual upwelling regime is documented across 21-35 degrees N and a seasonal regime across 12-19 degrees N, in accordance with the climatology of previous studies. Upwelling regions were split into three zones: (1) the Mauritania-Senegalese upwelling zone (12-19 degrees N), (2) the strong permanent annual upwelling zone (21-26 degrees N) and (3) the weak permanent upwelling zone (26-35 degrees N). We find compelling evidence in our various indices for the Bakun upwelling intensification hypothesis due to a significant coastal summer wind speed increase, resulting in an increase in upwelling-favorable wind speeds north of 20 degrees N and an increase in downwelling-favorable winds south of 20 degrees N. The North Atlantic Oscillation plays a leading role in modifying interannual variability during the other seasons (autumn-spring), with its influence dominating in winter. The East Atlantic pattern shows a strong correlation with upwelling during spring, while El Nino Southern Oscillation and Atlantic Multi-decadal Oscillation teleconnections were not found. A disagreement between observationally-based wind speed products and reanalysisderived data is explored. A modification to the Bakun upwelling intensification hypothesis for NW Africa is presented, which accounts for the latitudinal divide in summer wind regimes. (C) 2014 The Authors. Published by Elsevier Ltd.