Nano- and microplankton, chlorophyll a, b and c, and macronutrients from Ana Maria Gayoso cruise in the South western Atlantic during late spring 2021

The abundance of protistan plankton (cell size > 5 µm), along with the concentrations of photosynthetic pigments and dissolved inorganic nutrients, was assessed in the Southwestern Atlantic (SWA, 36-48ºS, 64-54ºW). This study covered three regions: the outer Patagonian shelf, the slope waters in the core of the Malvinas Current, and the adjacent open ocean in the Argentine Basin. Water samples from surface (5 m depth) and subsurface (10-30 m depth, in the subsurface chlorophyll maxima) layers were collected using Niskin bottles during late spring (November 2021) on the Ana Maria Gayoso oceanographic cruise aboard the vessel Bernardo Houssay, totaling 10 sampling stations. Plankton samples were analyzed under an optical microscope using the inverted microscope technique with sedimentation chambers. Cells were enumerated and identified to the species, genus, or family level and subsequently categorized into taxonomic groups: diatoms, phototrophic (including mixotrophic) and heterotrophic dinoflagellates, coccolithophores, nanoflagellates, and ciliates. Cell biovolume was determined using geometric shapes, and carbon content was calculated using established carbon-to-volume values. The concentrations of chlorophyll a, b, and c, along with nitrite, nitrate, ammonium, phosphate, and silicate, were determined using a spectrophotometer. The region under study supports numerous commercially valuable fish species, highlighting the importance of documenting the physico-chemical factors influencing plankton biodiversity. These records are vital for understanding potential changes in population and community dynamics, which could subsequently impact the productivity of marine ecosystems.