Uncoupled changes in phytoplankton biomass and size structure in the western tropical Atlantic

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 spring fall, over a coast-offshore gradient to investigate structure the Southwestern Tropical Atlantic (SWTA). Results revealed predominant role of thermohaline as main driver regardless season. In thermocline nutricline shallowing promoted biomass increase, which was 3-fold higher around oceanic islands. The community mainly varied vertically, with Prochlorococcus pigments contributing greatly nutrient Deep Chlorophyll Maximum, whereas other Cyanophyceae predominated poor surface layers during seasons. addition, clear variability new production (Fp) observed, shelf region displaying values (up 0.21), by larger Bacillariophyceae concentration, thus suggesting coastal production. Although increased seasonally, our results highlighted predominance recycled uncoupled between size structure, pico- nanophytoplankton dominating relative biomass, i.e., ca. 80% both We hypothesize that these patterns may result strong nitrogen limitation (N:P 3:1), likely constrain pronounced growth microphytoplankton.