Strong far-field coherent scattering of ultraviolet radiation by holococcolithophores

By considering the structure of holococcoliths (calcite plates that cover holococcolithophores, a haploid phase of the coccolithophore life cycle) as a photonic structure, we apply a discrete dipolar approximation to study the light backscattering properties of these algae. We show that some holococcolith structures have the ability to scatter the ultraviolet radiation. This property may represent an advantage for holococcolithophores possessing it, by allowing them to live higher in the water column than other coccolithophores.

Figure 1

(a) Calcidiscus leptoporus HOL (formerly Crystallolithus rigidus). (b) Helicosphaera carteri HOL (formerly Syracolithus catilliferus). In both cases, images are taken from Ref. 16 (Figs. 62D and 10D, respectively) and the scale bar is $1\mathrm{\mu }\mathrm{m}$.

Figure 2

Model with spheres representing the two layers observed in holococcoliths as those shown in Fig. 1. Spheres with a radius of $0.045\mathrm{\mu }\mathrm{m}$ are arranged in a plane of hexagons (dark spheres) with an edge length of $0.09\mathrm{\mu }\mathrm{m}$, covered by a triangular layer (light gray spheres) with an edge length of $0.16\mathrm{\mu }\mathrm{m}$. The separation between planes is $0.09\mathrm{\mu }\mathrm{m}$.

Figure 3

(Color online) Radiation backscattering of the periodic structure shown in Fig. 2.

Figure 4

(Color online) Radiation backscattering of the amorphous structure.