Figure 1. Cellular compartmental configuration and fluxes as modelled.

Chemical and isotopic equilibrium is assumed in the external medium, but neither is assumed inside the cell. Labelling of fluxes and compartments follows the convention of Hopkinson et al.⁴⁶ and Bolton and Stoll (ref. ²). Nomenclature is as follows: C, B refer to Carbon dioxide (CO₂) and Bicarbonate () respectively. Subscripts e, i, x and v refer to compartments: external, cytosol, choroplast and coccolith vesicle respectively (NB: subscript cell refers to outer cell membrane, whilst subscript i refers to cytosol. V_i=V_cell−V_x−V_v). FΘ_ab represents the flux of carbon species Θ, from compartment a to compartment b in units of mols⁻¹. FΘΦ_a represents the rate of conversion of carbon species Θ, to carbon species Φ, in compartment a, in units of mols⁻¹. Θ_a represents the concentration of carbon species, Θ, in compartment a in units of molm⁻³. P_Θa represents the permeability of compartment a membrane to carbon species Θ in units of ms⁻¹. V_a, SA_a represent the volume and surface area of compartment, a in units of m³ and m² respectively. f_a, s_a represents the scale and shape factor of compartment a, for inferring V_a and SA_a ([Dimensionless]). See ‘Methods' section for full model derivation and parameter values.