Picoeukaryotic phytoplankton observations from available public repositories and primary sources. Picoeukaryotic phytoplankton are defined as red fluorescent cells larger than Prochlorococcus and less than 2-3 µm in cell diameter. We only considered cell counts by flow cytometry. Samples covered a latitudinal range from 71.4˚N to 66.1˚S up to 400 m depth. Ancillary temperature and nitrate records were available for all but 2,334 and 6,530 observations, respectively, which we complemented with 1° monthly depth-dependent averages from the World Ocean Atlas (www.nodc.noaa.gov). To avoid analytical issues with detection limits, we imposed a minimum nitrate concentration of 0.01 μM. We calculated surface PAR (8 d averaged, 0.047° grid cell) using SeaWiFS and MODIS observations. Downward PAR was estimated using the attenuation coefficient K₄₉₀ from SeaWiFS and MODIS (http://oceancolor.gsfc.nasa.gov) and corrected for chlorophyll a³⁰, and a minimum of 10⁻³ E/m²d was imposed. Latitude, longitude, sample year, date and depth are provided with the field sample.