Fig. 1: Global patterns in Prochlorococcus division rates (d⁻¹) in surface waters.

a, Geographic distribution of daily division rates derived from the matrix population model (n = 180 independent samples), along with publicly available data from dilution experiments^{24,26,27,28,29,30,31} (n = 103 independent samples) and cell cycle analysis^20,23,24,25 (n = 11 independent samples). The vertical bars represent methodological uncertainties associated with the matrix population model and cell cycle analysis; uncertainty estimates were not reported for dilution experiments. The inset map shows sampling locations coloured by methodology. b–e, Relationships between division rates and environmental variables: daily average seawater temperature (°C) (b), daily average photosynthetically active radiation (light, µmol E m⁻² s⁻¹) (c) and phosphate (d) and nitrate (e) concentrations (nmol l⁻¹). Temperature and light were directly measured in situ for all methodologies. Nutrient data sources varied by methodology: for the matrix population model, 21 out of 180 measurements came from direct observations and 159 out of 180 came from the Mercator-PISCES biogeochemical model; for cell cycle and dilution experiments, 65 out of 114 included measured nutrient data while the remainder was omitted from the plot. Statistical relationships were assessed using ordinary least squares regression with two-sided tests (α = 0.01). The black line in b shows a second-order polynomial regression fit (P = 5.746 × 10⁻⁹), while the black lines in c–e show linear regression fits to the respective environmental factors. No adjustments for multiple comparisons were applied.