Ultraviolet Radiation – 22 CONCLUSIONS Crater Lake Color and UVR Transparency

Ultraviolet Radiation and Bio-optics in Crater Lake, Oregon, 2005



Crater Lake Color and UVR Transparency

Our recent UVR measurements show that Crater Lake is unusually transparent to UVR and visible wavelengths. In the DNA-damaging UV-B wavelengths diffuse attenuation ranges over values that are similar to, but in some cases more transparent than, other natural waters reported to date. Under average summer conditions (1996–2002) the intensity of a UV-B reference waveband (8-nm waveband centered at 320 nm) at 20 meters was 27% of surface irradiance, and at 40 meters was 5% of surface irradiance (10% at 40 meters under the especially clear conditions in 2001). The lowest UV-B diffuse attenuation coefficients (Kd,320) were somewhat lower than those reported for the clearest natural waters elsewhere (Lake Vanda, Antarctica, and several oligotrophic ocean regions), and were lower than the previously estimated attenuation by pure water (Smith & Baker, 1981).

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