## 4 Time-Varying Environmental Influences
### Stratified Oceans  
With respect to the availability of sunlight underwater, the ocean is divided into three zones. The euphotic zone is the uppermost section with an abundance of light and usually reaches a depth of about 200 m in clear waters. Beneath it is the disphotic zone, in which much of the yellow and red spectra have already been absorbed but blue-green spectra remain. This is typically 1 km deep. Beyond this is the aphotic zone, in which all downwelling light has diminished [54]. Due to the assumptions made in the determination of Jerlov types, modeling mobile UOWC performance using the coefficients reported by [PERSON] would be unrealistic beyond a depth of about 10 m. Instead, the flexibility of modeling optical characteristics at a given ocean location or depth would be an ideal scenario. Ocean color sensors on Earth observation satellites, such as the Sea-viewing Wide Field-of-view Sensor (Sea WiFS) and the Ocean Color and Temperature Scanner, have been used for a long time to monitor the distribution of chlorophyll-a (Chl-\(a\)) concentration at the sea surface, the principal pigment in chlorophyll [55]. Using these data, the vertical distribution of Chl-\(a\) concentration may be modeled [33; 34; 55]. Given the abundance of sunlight closer to the surface, chlorophyll concentration is primarily influenced by nutrient availability. However, with increasing depth and a lesser penetration of sunlight, photosynthesis is constrained, leading to a decrease in chlorophyll concentration. Within the transitional zone between sunlit, nutrient-poor waters and dark, nutrient-rich waters, a peak in chlorophyll concentration (deep chlorophyll maximum or DCM) is observed. The depth of this DCM typically falls within the range of 20 to 120 m, contingent on the surface concentration of chlorophyll [52; 32]. The consistency of this phenomenon, described as a relative Gaussian distribution, has led to the development of models correlated with empirical data for the Chl-\(a\) concentration along a vertical column of water [55]. Furthermore, these models are consistent for oceans that are stratified, a very common occurrence, where the depth layers do not mix, thus enabling parameterization [34]. [PERSON] et al. have further extended this knowledge by classifying observations at 1821 stations across the globe into nine different ocean types: S1-S9, by order of surface Chl-\(a\) concentration (Figure 5) [34]. Their dimensionless parameterized Equation (5) and respective parameters are shown below and in Table 2, respectively, where \(C_{b}\) is the surface chlorophyll concentration; \(s\) is the vertical gradient of chlorophyll concentration; \(\zeta\) is the  
Figure 4: Spectral distribution of global irradiance generated for a clear summer day in Auckland, New Zealand, using SPCTRL2 on 7 December 2023 at 11:30 am; coordinates, 36.8509 S, 174.7645 E; 2.2 cm precipitable water vapor, 1013 mb atmospheric pressure, and 300 DU ozone coverage [52]. dimensionless depth normalized for the euphotic depth \(Z_{eu}\) in meters; \(C_{max}\) is the Chl-\(a\) concentration at the depth \(\zeta_{max}\) of the subsurface maximum; and \(\overline{Chl\text{-}a_{Z_{eu}}}\) is the average Chl-\(a\) concentration (mg m\({}^{-3}\)) within the euphotic layer. This can be reconstructed into a dimensioned form \(C_{c}(S,z)\) by using (6) and (7). S5-S8 are only plotted for a maximum depth of 110 m due to the Chl-\(a\) concentration approaching zero. It should also be noted that the characteristics of S9 cannot be modeled beyond shallow depths due to the fact that the value of's' given is 0 [34]. \[C_{DL}(\zeta)=C_{b}-s\zeta+C_{max}e^{-\left[\frac{z-f_{max}}{\Delta s }\right]^{2}} \tag{5}\] \[C_{c}(\zeta)=C_{DL}(\zeta)\times\overline{Chl\text{-}a_{Z_{eu}}}\] (6) \[z=\zeta\times Z_{eu} \tag{7}\]  
Another parameterized version of these data, for [PERSON] and [PERSON]'s equation, is presented by [PERSON] et al.