## 3 Results and Discussion  
### Contrasting Examples of Light Field Characteristics and AOPs  
Our measurements show that the bio-optical properties within the Gulf of California exhibited a large range of variability, which is summarized in terms of _Chl_ and \(c_{p}\)(660) data in Table 2. The examined water column extended from the surface to a maximum measurement depth of 80 m. The depth of euphotic layer, \(z_{eu}\), was determined using a conventional criterion by estimating a depth at which the surface PAR (i.e., \(E_{oPAR}\)) was reduced to 1%. The depth \(z_{eu}\) ranged from about 30 to 60 m depending on time and location of measurement. Typically, our measurements (at least in the blue-green spectral region) extended \(\sim\)10-30 m below \(z_{eu}\), and these maximum measurement depths corresponded to \(\sim\)0.1-0.5% of surface \(E_{oPAR}\). Because phytoplankton have specific energetic demand rather than demand for percentage of light, it is reasonable to expect that the compensation depth of phytoplankton photosynthesis for specific latitude, season, and optical water types investigated in our study was greater than \(z_{eu}\), probably closer to 0.1% of surface PAR [87]. Therefore, we refer to the entire investigated water column as the euphotic layer. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Depth of Measurement** & **Shallowest** & **Greatest** & _Chl_ **Maximum** \\ \hline \(z\) (m) & 5.4 \(\pm\) 2.9 & 64.9 \(\pm\) 12.1 & 33.0 \(\pm\) 9.9 \\  & (1.2, 10.5) & (47.6, 80.7) & (20.4, 50.5) \\ \hline \(Chl\) (mg m\({}^{-3}\)) & 0.067 \(\pm\) 0.067 & 0.13 \(\pm\) 0.15 & 0.81 \(\pm\) 0.54 \\  & (0.005, 0.24) & (0.004, 0.42) & (0.25, 2.17) \\ \hline \(c_{p}\)(660) (m\({}^{-1}\)) & 0.173 \(\pm\) 0.035 & 0.089 \(\pm\) 0.048 & 0.239 \(\pm\) 0.076 \\  & (0.103, 0.238) & (0.043, 0.202) & (0.125, 0.405) \\ \hline Solar zenith angle \(\theta_{s}\) (degrees) & 0.5–57.1 & & \\ \hline \multirow{2}{*}{Euphotic depth \(z_{eu}\) (m)} & 40.5 \(\pm\) 8.9 & & \\  & (29.3, 60.0) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of data characterizing the shallowest and greatest depths of radiometric measurements, the depth of chlorophyll-\(a\) maximum, and the corresponding chlorophyll-\(a\) concentration, _Chl_, and particulate beam attenuation coefficient at 660 nm, \(c_{p}\)(660), for these depths based on all stations during the 2010 and 2011 cruises in the Gulf of California. For each of these variables the average value \(\pm\) standard deviation with the minimum and maximum values in parenthesis are given. In addition, the minimum and maximum values of the solar zenith angle \(\theta_{s}\) and the data characterizing the euphotic depth \(z_{eu}\) (the average value \(\pm\) standard deviation with the minimum and maximum values in parenthesis) are shown for all stations. Within the examined water column, _Chl_ varied from extremely low levels on the order of 10\({}^{-3}\) to more than 2 mg m\({}^{-3}\) with the highest values observed within the _Chl_ maximum (_Chl\({}_{max}\)_) layer and the lowest values either near the surface or at the deepest measurement depths (\(\sim\)60-80 m). The shape of the _Chl\((z)\)_ vertical profile also changed significantly within the study area. The depth \(z_{Chlmax}\) of _Chl\({}_{max}\)_ ranged from about 20 m to 50 m. The full width half maximum (FWHM) of the _Chl\({}_{max}\)_ layer, when fitted to a Gaussian function, ranged from 5 m to 30 m. Significant variations spanning one order of magnitude from about 0.04 to 0.4 m\({}^{-1}\) were also observed in \(c_{p}(z,\,660)\). In addition, our measurements were conducted under a broad range of the solar zenith angle, \(\theta_{s}\), varying between 0.5\({}^{\circ}\) (i.e., the sun nearly at zenith) to 57.1\({}^{\circ}\). Such broad range of environmental conditions is evident in terms of diverse scenarios in the measured light field characteristics and AOPs.