Abundance of microbial phytoplankton through the water column during the AMT23 (JR20131005/JR300) cruise in October-November 2013.

This dataset contains depth profiles of the mean abundance of cyanobacteria and small (&lt;20 um) phytoplankton reported in cells per millilitre. Samples were measured using flow cytometry during the Atlantic Meridional Transect (AMT) cruise AMT23 (JR20131005/JR300). The samples were collected between October and November 2013 from 200 m to the surface, using a Seabird CTD system with a rosette of 24 Niskin bottles of 20 L volume. Samples were collected from the predawn and noon CTDs and were stored in a refrigerator and analysed within 3 hours of collection. In total 730 discrete samples were analysed and quantified using a Becton Dickinson FACSort flow cytometer which characterised and enumerated <em>Prochlorococcus</em> sp. and <em>Synechococcus</em> sp. (cyanobacteria) and pico- and eukaryotic phytoplankton, based on their light scattering and autofluorescence properties. Data were analysed onboard the ship during the cruise.