Radenac Marie-Hélène auteur aut IRD Jouanno Julien auteur aut IRD Tchamabi Christine Carine auteur aut IRD Awo M. auteur aut IRD Bourlès Bernard auteur aut IRD Arnault Sabine auteur aut IRD Aumont Olivier auteur aut IRD text journalArticle eng text/pdf reformatted digital access Ocean color observations show semiannual variations in chlorophyll in the Atlantic cold tongue with a main bloom in boreal summer and a secondary bloom in December. In this study, ocean color and in situ measurements and a coupled physical-biogeochemical model are used to investigate the processes that drive this variability. Results show that the main phytoplankton bloom in July-August is driven by a strong vertical supply of nitrate in May-July, and the secondary bloom in December is driven by a shorter and moderate supply in November. The upper ocean nitrate balance is analyzed and shows that vertical advection controls the nitrate input in the equatorial euphotic layer and that vertical diffusion and meridional advection are key in extending and shaping the bloom off Equator. Below the mixed layer, observations and modeling show that the Equatorial Undercurrent brings low-nitrate water (relative to off-equatorial surrounding waters) but still rich enough to enhance the cold tongue productivity. Our results also give insights into the influence of intraseasonal processes in these exchanges. The submonthly meridional advection significantly contributes to the nitrate decrease below the mixed layer. specialized ATLANTIQUE 032 036 17 2 529-545 2020 1726-4170 https://www.documentation.ird.fr/hor/fdi:010077892 10.5194/bg-17-529-2020 1726-4170 [F B010077892] https://www.documentation.ird.fr/hor/fdi:010077892 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers20-02/010077892.pdf IRD - Base Horizon / Pleins textes 2020-03-11 2025-02-24 fdi:010077892 fre