Physical drivers of the nitrate seasonal variability in the Atlantic cold tongue

摘要: Abstract. Ocean color observations show semiannual variations in chlorophyll in the Atlantic cold tongue with a main bloom boreal summer and secondary December. In this study, ocean and situ measurements coupled physical–biogeochemical model are used to investigate processes that drive variability. Results the main phytoplankton July–August is driven by strong vertical supply of nitrate May–July, December driven by shorter moderate supply November. The upper nitrate balance analyzed shows vertical advection controls nitrate input equatorial euphotic layer diffusion and meridional key extending shaping off Equator. Below mixed layer, modeling Equatorial Undercurrent brings low-nitrate water (relative to off-equatorial surrounding waters) but still rich enough enhance tongue productivity. Our results also give insights into influence of intraseasonal these exchanges. submonthly meridional advection significantly contributes decrease below mixed layer.