Figure 10B. Crater Lake Kd,320 (10–40 m) versus surface Chl-a (0–30 m, retained on0.45 micron filter) for July and August 1984–2002. Only “dry” months and several months with heavy but frozen precipitation are included in the regression. Regression equation for warm dry months, y = 0.15x + 0.08 (r2 = 0.44).

Figure 11A. Crater Lake empirical model for Kd,380 versus depth based on bio-optical signals (20 August 2001). Temperature and depth from Seabird CTD; chlorophyll fluorescence (Fchl, relative units) from Wetlabs WetStar fluorometer;cp660 from SeaTech transmissometer (cw=0.411 m-1); Kd,380 (open circles) from LI-1800uw scans. Model: Kd,380= 0.40*Fchl + 0.36*cp660.

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).

Figure 12B. Absorption ratios consistent with photo protection from UV-B in phytoplankton near the surface (MAA peak versus Chlorophyll-a red peak ratio follows attenuation trend for UV-B irradiance; Chlorophyll-a blue peak versus Chlorophyll-a red peak ratio remains constant with depth). Ratio of Fchl:cp660 shows photoacclimation as in Figure 11B.