A, Photosynthesis versus irradiance curve under PAR (white circles) and PAR + UVR (black circles) conditions; dotted lines represent 95% confident limit. The mean irradiances (PAR, UV-A, and UV-B) during the incubations (August 6 and 8, 2005) were 321, 50.5, and 2.1 W m−2, respectively. B, Vertical distribution of estimated daily photosynthetic production on a sunny day (black symbols; July 5, 2006) and a cloudy (white symbols; August 13, 2006) day. The doses (and mean irradiances) of PAR for these days were 14 (280 W m−2) and 0.9 MJ m−2 (19.6 W m−2), respectively. Note that even on the sunny day without cloud coverage, UVR enhanced production (shaded areas) is larger than the UVR-related reduction (open area enclosed by the lines).