## 5 Results
### Accuracy of Numerical Computations
When mineral particles are taken into account, \(\Delta\epsilon\) is 12% between the \"Homogeneous reference case 3\" and the coastal-like water body. This smaller difference is because phytoplankton have a smaller impact on the bulk scattering when highly scattering particles such as minerals are added. The impact of the relative volume of the cytoplasm on \(\widetilde{b^{\theta_{s}}_{up}}\) is now evaluated by comparing the change of \(\widetilde{b^{\theta_{s}}_{up}}\) as a function of \(\xi\) for the 80%-20% and 70%-30% models for the oligotrophic-like and phytoplankton bloom water bodies (Figure 6). The mean relative difference in \(\widetilde{b^{\theta_{s}}_{up}}\) is about 5.41% with a maximum value of 11.5 % (\(\xi\) = 3) for oligotrophic-like case study. In bloom conditions, the mean relative difference reaches 13.0% with a maximum value of 23.5% (\(\xi\) = 3.2). Figure 7 compares simulated \(\widetilde{b^{\theta_{s}}_{up}}\) when phytoplankton cells are modeled as two-layered spheres (80%-20%) or three-layered spheres (80%-18.5%-1.5%). For the oligotrophic-like waters, relative absolute differences are small. They range between 0.0174% and 1.81% with a mean value of 0.444%. For phytoplankton bloom case study, they are between 9.84 \(\times\) 10\({}^{-3}\) and 2.86% with a mean value of 0.894%. Regardless of the morphological model used to optically simulate phytoplankton cells, the \(\widetilde{b^{\theta_{s}}_{up}}\) reaches an asymptote when \(\xi\) decreases for phytoplankton bloom water bodies (\(\widetilde{b^{\theta_{s}}_{up}}\) = 0.005 for \(\xi\) = 3.5 and 0.004 for \(\xi\) = 2.5). The value of the asymptote is consistent with previous observations [5], which showed the lowest backscattering ratio (about 0.005) in waters with high chlorophyll-a concentration. The contribution of the different particle groups to the backscattering ratio is presented in Figure 8 for the 80%-20% model and \(\xi\) = 4. For coastal-like waters, the minerals contribute more than 80% of the total \(\widetilde{b^{\theta_{s}}_{up}}\), whereas they contribute only 6.5% to the total particulate abundance. This percentage agrees with the results of [PERSON] et al. [25] (Figure 12 in their paper). Such high contribution to backscattering is due to the high real refractive index of minerals. As in [PERSON] et al. [25], these results show the important role of minerals even when they are less abundant than organic living and non-living particles. In oligotrophic-like waters, the contribution of heterotrophic bacteria ranges from a few to about 30% with a maximum for \(\xi\) between 3.5 and 4, which agrees with [PERSON] and [PERSON] [24]. The contribution of viruses is quite high, about 40-60% for \(\xi\) between 4 and 5. This high contribution is explained by the extreme value of viral abundance (around 1 \(\times\) 10\({}^{14}\) particles per cubic meter) used in this study [24]. As for bacteria, the contribution of phytoplankton ranges between a few and 30% with a maximum around \(\xi\) = 3. For a \(\xi\) value of 4, typical of oligotrophic waters, the contribution is around 10%. For the phytoplankton bloom study case, the contribution of phytoplankton cells is between 10% and 60%; maximum values are reached for a PSD slope between 3 and 3.5. Such high percentages are due to the higher backscattering cross section of phytoplankton as compared to the other particles (Figure 9). The low phytoplankton abundance is offset by the high \(C^{bb}_{sca,PHY}\) so that the backscattering coefficient of phytoplankton represents a significant contribution to the total backscattering. Figure 6: Particulate backscattering ratio as a function of the hyperbolic slope for oligotrophic-like and phytoplankton bloom water bodies. Phytoplankton cells are modeled as two-layered spheres with a relative volume of the chloroplast of 20 % and 30 %, as indicated. Figure 7: Particulate backscattering ratio as a function of the hyperbolic slope for oligotrophic-like and phytoplankton bloom water bodies.