Coccolithophore living communities from CTD samples taken during JR18001 (AMT28) in the North and Equatorial Atlantic Ocean between September and October 2018.

This dataset contains coccolithophore abundance (cells/L) data collected across the photic zone of the Atlantic Ocean between 50° N and 1° S during the 28th Atlantic Meridional Transect cruise (AMT28/JR18001). In total, 150 Samples were collected between the 25th of September and 10th of October 2018 at 30 CTD stations (CTD casts 1-30; stations 1-31). Samples were collected at discrete water depth levels between 5 and 200 m depth to assess the distribution of coccolithophore species along the photic zone of the ocean. For each sample depth, between 2 and 5 Litres of sample water was filtered onto cellulose acetate filters (0.45 mm pore size, 47 mm diameter). The filters were then rinsed with a buffered solution to remove salt, dried at room temperature, and stored in petri dishes. A randomly chosen section (approx. 30°-45°) of each filter (radius of ~16 mm) was cut and permanently mounted on a glass slide. Coccospheres (cells) were identified and counted under polarized light microscope (Zeiss Ortholux II-POL-BK). The number of cells per litre (cells/L) was estimated from the number of counted coccospheres in the examined area, multiplied by the ratio of total filter area to examined area, and divided by the volume of filtered water (Cros, 2001). 26 samples containing higher numbers of rare species and holoccocolithophores were inspected using a Scanning Electron Microscope (SEM, JEOL JSM5200-LV at FCUL) to refine the differentiation of Syracosphaera spp., Ophiaster spp., Michaelsarsia spp., Acanthoica spp. and holococcolithophores. A randomly chosen section of the selected filters was fixed with carbon tape on a SEM stub and sputtered with a gold (Au) coating. Coccolithophore taxa were further grouped according to their similarities in terms of meridional and in-depth distribution during AMT28, following similar criteria to those of Young (1994).