## 3 Results and Discussion
### Contrasting Examples of Light Field Characteristics and AOPs
This was primarily because the effect of Raman scattering generally led to a gradual decrease of \(K\)-coefficients in the red, for example at 650 nm, with increasing depth until approaching the level of \(K\)-coefficients in the blue and green. This pattern that eventually led to relatively flat \(K\)-coefficients has been demonstrated previously in experimental data and theoretical results from RT simulations [37; 64; 73]. It is, however, important to emphasize that we do not suggest that the light field in the examined case has reached an asymptotic regime within the deepest portion of the examined layer (i.e., \(\sim\)60-70 m) where we observe such similarity of \(K\)-coefficients and relatively constant AOPs with depth. While such patterns can be associated with the asymptotic regime, previous deep-sea RT simulations demonstrated that a nearly asymptotic light field could generally be reached only at significantly greater depths within the ocean mesopelagic zone [64; 73]. For comparison with the results discussed above in the Guaymas Basin, Figure 7 shows the vertical profiles of AOPs obtained from measurements at a station in the Farallon Basin where the \(Chl_{max}\) layer was significantly broader with a two-fold higher \(Chl_{max}\) and the solar elevation was significantly lower (see Figure 2). As a result of these differences in the environmental conditions, which could also include differences in the IOPs, some features of AOPs measured in the Farallon Basin were different compared to those in the Guaymas Basin. We note, however, that the data from the Farallon Basin do not extend throughout the entire \(Chl_{max}\) layer but end at 40 m which is about 10 m below \(z_{Chlmax}\). The values of the average cosines in the blue-green spectral region in the Farallon Basin were much lower (Figure 7a-c) than those in the Guaymas Basin (Figure 5f-h). The lower values of \(\overline{\mu}_{d}\) and \(\overline{\mu}\) in the blue and green can be explained by the higher solar zenith angle and slightly higher IOPs as indicated by the \(c_{p}\)(z, 660) profiles (Figure 2b). This result is consistent with previous experimental and modeling results [92; 93; 94; 92; 90]. The observation of very low values (0.25-0.35) of \(\overline{\mu}_{u}\) in the blue and green (Figure 7b) will be discussed is some detail in Section 3.2.1, but it is interesting to note that the values less than 0.35 were previously reported on the basis of RT simulations of highly scattering environment within near-surface bubble clouds [91]. In the red where the effects of inelastic processes are strong, the vertical profiles of average cosines exhibited similar features to those described earlier for the station in the Guaymas Basin. Overall, our data of the average cosines support the notion that sun position in a clear sky sets the values of \(\overline{\mu}_{d}\) and \(\overline{\mu}\) near the ocean surface, which then change with depth in a manner dependent on the interplay of the vertical structure of IOPs and inelastic processes, and \(\overline{\mu}_{u}\) may vary within a broader range than commonly assumed. It is thus important to emphasize that the average cosines are sensitive to surface illumination, especially for the downwelling and total light in the near-surface layer, so these average cosines may potentially serve as AOPs or useful descriptors of near-surface water bodies only under specified surface boundary conditions. The vertical profiles of \(R\) in the Farallon Basin (Figure 7d) showed patterns that were similar to those observed in the Guaymas Basin (Figure 5e), but the \(R\) values were generally higher because of higher \(Chl\) and water turbidity at the station in the Farallon Basin. The properties of particulate assemblages, including the composition and size distribution, could have also been different at these stations. The \(K_{d}\) and \(K_{u}\) values within the \(Chl_{max}\) layer in the Farallon Basin (Figure 7e,f) were not as low as in the examined case from the Guaymas Basin (Figure 6e,g).