Fig. 2.

Calculated diffusive flux of HCO₃^– [J = r^–2 [r′r (r′ – r) D (C_m – C_o)]; Nobel, 1983] as a function of radius (r) for spherical colonies exposed to three ambient concentration levels (C_m: 0·1, 0·5 and 2·0 mm HCO₃^–) and three levels of boundary layer thickness (DBL: δ = r′ – r; 0·3, 1·0 and 3·0 mm). The combinations are indicated in the key in the figure, with C_m first and δ second. The molecular diffusion coefficient (D) is set at 1·0 × 10^–9 m² s^–1 (Zeebe, 2011) and the HCO₃^– concentration at the colony surface is assumed to be zero.