Figure 1A. Crater Lake solar irradiance spectra (304–750 nm) at depths 20–160 m, 20 August 2001 (air scan 12:04 PDT). LI-COR LI-1800uw spectroradiometer (8 nm bandwidth; cosine response to downwelling irradiance). Incident Ed irradiance (thick line) plotted along with model Eo irradiance (thin line, distinct from the measurements only at the lowest and highest wavelengths) from RTBasic (Biospherical Instruments; 8-stream option, 2 nm bandwidth; model output adjusted using 8 nm running averages of model Log (Ed) to account for the 8 nm bandwidth of the LI-1800uw data; ozone=313 DU from satellite; Patm=774 torr from elevation). Ratios of measured:modeled data averaged 98% for 308–800 nm, and 96% for 308–400 nm (range 87–109%).

Figure 11B. Crater Lake phytoplankton photoacclimation index for 2001 (from ratio of biooptical signals, Fchl:cp660).

Figure 12A. Crater Lake particulate absorption (ap) spectra from 5 depths (20 August 2001). QFT method as modified by Lohrenz (2000) using GF/F filters (0.5–1.0 liters filtered); filter supported on quartz disc and scanned using a Shimadzu 160-UV spectrophotometer. Chlorophyll-a absorption peaks at 675 nm and 430 nm; apparent micosporine-like amino acid (MAA) peak at 325 nm (arrow) clearly visible in 25 m and 50 m samples. Chlorophyll-a concentrations calculated from 675 nm peaks (0.038–0.38 mg m-3 using ap*675=0.040) closely match the [Chlorophyll-a] calculated from data in Figure 3 using the diffuse attenuation model of Morel and Maritorena 2001. Typical ap*675 = 0.035 according to Sathyendranath et al. (1987).