Greatest linear dimension (GLD, µm) measurements as a proxy of the cell size, cell carbon estimates (pgC cell^-1), and carbon biomass assessments of dinoflagellates and diatoms cells are reported in this dataset. The phytoplankton samples were collected from the oceanic regions, Perdido and Coatzacoalcos, located in the Southern Gulf of Mexico. The information comes from four campaigns carried out during 2016 (MF1 cruise, late winter, and MF2 cruise, late summer), 2018 (MF3 cruise, spring), and 2019 (MF4 cruise, spring). The carbon data (pg C cell^-1) were based on biovolume calculations derived from linear dimension measurements of individual cells and the approximate geometric body shape of each genus. The biomass assessments (µg C L^-1) were performed using these carbon content factors and cell abundances. 

The data is a contribution of the Gulf of Mexico Research Consortium (CIGoM; http://www.cigom.info/). This data is openly shared for scientific research purposes, and authors request to be contacted prior to usage.