MERIDIONAL VARIATIONS OF THE SPRINGTIME PHYTOPLANKTON COMMUNITY IN THE SARGASSO SEA

The seasonal evolution of subtropical Mode water (18° water) is shown to be the primary factor controlling the spatial distribution and evolution of the phytoplankton community in the northern Sargasso Sea 31 to 35°N). The springtime near-surface restratification of recently ventilated 18° water initiated a diatom-dominated phytoplankton bloom. As the bloom declined, the phytoplankton community evolved into a diverse assemblage. South of the region of 18° water wintertime ventilation (S of 31°N), phytoplankton concentrations were considerably less and appeared to be regulated by different processes; influences of subtropical convergence fronts were observed. For the N Sargasso Sea, the wintertime ventilation of 18° water is the primary new nutrient flux into the euphotic zone, comprising most of the expected annual new production for this region. -from Authors