Farias G. B. auteur aut IRD Molinero Juan-Carlos auteur aut IRD Carré Claire auteur aut IRD Bertrand Arnaud auteur aut IRD Bec B. auteur aut IRD Melo Pamd auteur aut IRD text journalArticle eng text/pdf born digital access Structural changes in phytoplankton communities have large influence on marine elemental cycling, food web dynamics and carbon export. Here we used data from two field expeditions, performed in spring and fall, over a coast-offshore gradient to investigate phytoplankton structure and dynamics in the Southwestern Tropical Atlantic (SWTA). Results revealed a predominant role of the thermohaline structure as the main driver of phytoplankton dynamics regardless the season. In fall, the thermocline and nutricline shallowing promoted a biomass increase, which was 3-fold higher around the oceanic islands. The structure of phytoplankton com-munity mainly varied vertically, with Prochlorococcus pigments contributing greatly to the higher nutrient Deep Chlorophyll Maximum, whereas other Cyanophyceae predominated in nutrient poor surface layers during the two seasons. In addition, a clear coast-offshore variability in the new production (Fp) was observed, with the shelf region displaying higher values (up to 0.21), promoted by larger Bacillariophyceae pigments concentration, thus suggesting a coastal influence on shelf production. Although the phytoplankton biomass increased seasonally, our results highlighted a predominance of recycled production (Fp) and uncoupled dynamics between biomass and size of phytoplankton structure, with pico-and nanophytoplankton dominating the relative biomass, i.e., ca. 80% of the community in both seasons. We hypothesize that these patterns may result from a strong nitrogen limitation (N:P of around 3:1), which likely constrain a pronounced growth of the microphytoplankton. specialized Primary producers dynamics Pigment composition Tropical thermohaline structure Nutrient ratios ATLANTIQUE BRESIL ZONE TROPICALE 036 034 227 103696 [12 ] 2022 0924-7963 https://www.documentation.ird.fr/hor/fdi:010083920 10.1016/j.jmarsys.2021.103696 0924-7963 [F B010083920] https://www.documentation.ird.fr/hor/fdi:010083920 https://www.documentation.ird.fr/intranet/publi/2022-02/010083920.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2022-02-04 2025-02-24 fdi:010083920 fre