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Fig. 3 Daily dynamics of the fucoxanthin pigments plotted alongside irradiance (photons m-2 s-1; solid line) in iron-limited (Fe-) and iron-replete (Fe+) cells. (A, D) Ratio of

19'-hexanoyloxyfucoxanthin to fucoxanthin (hexa/fuco). (B, E) Ratio of fucoxanthin to chlorophyll a. (C, F) Ratio of 19'hexanoyloxyfucoxanthin to chlorophyll a

(HEXA/FUCO) decreased towards the end of the light period (Fig. 3A; P < 0.05), which was associated with a 50% increase in FUCO/Chl a (Fig. 3B), whereas HEXA/Chl a remained invariable at a high level (Fig. 3C). In iron-replete cells, no significant daily dynamics in HEXA and FUCO were observed (Fig. 3D-F).

In both treatments, the in vivo light absorption characteristics were invariable over the day (data not shown). Maximum values in the chlorophyll-specific absorption coefficient were observed near 675 nm (Chl a), 470 nm (carotenoids) and 430 nm (Chl a) (Fig. 4). The absorption cross section was 0.057 m2 mg Chl a-1 under iron limitation and

Phaeocystis antarctica

Phaeocystis antarctica

500 600

Wavelength (nm)

Fig. 4 In vivo absorption spectra expressed per chlorophyll a for iron-limited (open symbols) and iron-replete cells (closed symbols)

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