Figure 4.

ProMolec results. (a) Diel cycles in incident irradiance (PAR; μmol quanta m⁻² s⁻¹; solid line, offset right axis), chlorophyll-specific light-saturated carbon fixation (${\text{P}}_{\text{max}}^b$; mg C mg chl⁻¹ h⁻¹; filled circles, left axis), and the chlorophyll-specific light-limited slope for carbon fixation (α^b; mg C m² s (mg Chl h μmol quanta)⁻¹; open circles, right axis). α^b has been corrected for midday photoinhibition effects using variable fluorescence data to demonstrate more clearly the strong correlation in the fraction of light-limited and light-saturated photosynthate used for carbon fixation. (b) Diel carbon fixation rate (fg C cell⁻¹ h⁻¹; filled circles) calculated from CI data and incident light (a) and cellular carbon accumulation rate (fg C cell⁻¹ h⁻¹; open circles). (c) Diel cycles in cellular N:C ratios normalized to the average value measured at midnight (filled circles) and fraction of cells in G1 phase (open circles, right axis). Solid line indicates PAR. Vertical dotted line in each figure demarks period when carbon fixation dropped by greater than 60% (see text).