Inhibition of marine photosynthesis by ultraviolet radiation: Variable sensitivity of phytoplankton in the Weddell-Scotia Sea during austral spring

• Main Authors: Patrick J. Neale, John J. Cullen, Richard F. Davis
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1998
• Subjects: Antarctic; Austral; Scotia Sea; Southern Ocean; The Antarctic; Weddell; Antarc*
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.572.1559; http://www.aslo.org/lo/toc/vol_43/issue_3/0433.pdf

To assess the potential impacts of ozone depletion on photosynthesis in the Southern Ocean, we need to know more about effects of ultraviolet radiation (UV) on phytoplankton in Antarctic waters, where, in addition to variable stratospheric ozone, temporal and regional differences in vertical mixing might influence photosynthesis and pho-toacclimation of phytoplankton assemblages. Toward this end, we quantified the responses to UV of Antarctic phytoplankton in the Weddell-Scotia Confluence during the austral spring of 1993. Experimental results on spectral sensitivity of photosynthesis were fit statistically to a model that incorporated uninhibited photosynthesis as a function of photosynthetically available radiation (PAR), wavelength-dependence of inhibition, and the kinetics of photosynthesis during exposure to UV. In contrast to previous results on UV-induced photoinhibition in a diatom culture at 20°C natural phytoplankton from open waters of the Antarctic showed no ability to counter UV-induced inhibition of photosynthesis during exposures of 0.5-4 h: the rate of photosynthesis declined exponentially as a function of cumulative exposure, and inhibition was not reversed during incubations for up to 3.5 h under benign conditions. The results suggest that nonlinear exposure-response relationships are necessary for modeling UV-dependent photosynthesis in the surface mixed layer of the springtime Weddell-Scotia Confluence. Consequently, we modified our laboratory-based model of photosynthesis and photoinhibition to describe photoinhibition as a