The dataset consists of BD Influx-based analysis of picophytoplankton populations from discrete flow cytometry data collected underway during the University of Washington School of Oceanography undergraduate senior thesis cruise (TN398) during December 2021 from Honolulu to San Diego, crossing through the Great Pacific Garbage Patch. The data includes cell abundance, cell size (equivalent spherical diameter), carbon quota, and carbon biomass for picophytoplankton populations, namely the cyanobacteria Prochlorococcus, Synechococcus, and and small eukaryotic phytoplankton (<5 μm ESD). Time is in UTC format, latitude and longitude are in decimal degrees, and depth is in meters. Further information can be found here: https://github.com/fribalet/FCSplankton