Phytoplankton species counts from CTD samples collected in Atlantic Ocean surface waters during RRS Discovery DY157 (AMT30) February-March 2023

This dataset contains phytoplankton abundances, as cell numbers per taxa, collected in surface samples along a transect on the Atlantic Ocean, during the 30th Atlantic Meridional Transect cruise (AMT30/DY157). The samples were collected between February and March 2023 at 56 CTD stations, at 5 m depth between 46° S and 40° N. Samples were fixed and observations were carried out with a Zeiss Axiovert 200 inverted microscope. Cells > 10 µm were counted in a 50 mL chamber, following the Utermöhl method (Utermöhl, 1958). Species from the following divisions/classes were identified and counted from Lugol’s-fixed samples: Bacillaryophyceae (Diatoms), Dinophyceae, separated into Autotrophic (ADinos) and Heterotrophic Dinoflagellates (HDinos), Prasinophyceae, Cryptophyceae; furthermore the genus Phaeocystis and Filamentous Cyanobacteria belonging to three genera were also quantified. Coccolithophores were counted from the Formaldehyde-fixed samples.