MEPS 144:223-236 (1996)  -  doi:10.3354/meps144223

An in situ biological weighting function for UV inhibition of phytoplankton carbon fixation in the Southern Ocean

Boucher NP, Prézelin BB

A daily integrated in situ biological weighting function (BWF) for inhibition of primary production by ultraviolet radiation (UVR, 280 to 400 nm) was determined for a natural community of Antarctic diatoms maintained under daylight conditions. The derived daily averaged BWF had a radiation amplification factor of 0.91 for the environmental radiation conditions under which it was determined, and displayed greater sensitivity to UV-B than BWFs determined for laboratory cultures of temperate latitude phytoplankton (Cullen et al. 1992; Science 258:646-650). In addition, the function was shown to accurately predict the UVR-dependent in situ rates of primary production when the same community was under different stratospheric ozone (O3) conditions. An error estimate for the BWF is also provided and the predictive limitations of the function are discussed briefly. In the early austral spring of 1993 near Palmer Station, Antarctica, surface samples were maintained in 6 spectrally distinct outdoor incubators over the course of a single day and the spectral sensitivity of photosynthetic carbon fixation rates and phytoplankton pigmentation was quantified. The changes in spectral sensitivity to O3-dependent UV-B (280 to 320 nm radiation) and O3-independent UV-A (320 to 400 nm radiation) was resolved on time scale of 2 h intervals over the course of the 10 h incubation. Besides determining the daily peak of cell sensitivity to UVR damage, the derived short-term kinetics for the 6 different spectral light treatments provided the database for resolving a robust action spectrum for the UVR inhibition of in situ rates of primary production. For the diatom community being studied, daily exposure to ambient levels of UVR resulted in a 34% reduction in averaged carbon fixation without any significant effect on the cellular pigment content. The UV-B portion of the solar spectrum photoinhibited daily rates of primary production by 15%, while UV-A was responsible for a 19% reduction in daily averaged rates of carbon fixation. It appears that springtime diatom-dominated communities are equally or more sensitive to UV-B photoinhibition of daily primary production than prymnesiophyte-dominated communities, analyzed during the 1990 'Icecolors' expedition (Smith et al. 1992; Science 258:952-959).

UV · Primary production · Phytoplankton · Antarctica · Action spectra · Photoinhibition · Ozone

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