Solar ultraviolet radiation in the sea and photoinhibitory effects on natural phytoplankton populations

Jennifer Eileen Prentice, University of Rhode Island

Abstract

This study is the first to examine the spatio-temporal variability in the penetration of solar UVB (280–320 nm) and UVA (320–400 nm) radiation relative to PAR (400–700 nm) in productive coastal and open ocean waters. As a critical component of this work, an intercalibration and comparison of instruments for measuring underwater UV spectral irradiance was conducted. A multi-channel filter radiometer was the best performer and used to profile PAR and spectrally specific UV at 305, 320, 340, and 380 nm. Diffuse attenuation coefficients (K) were calculated and used to define the 1% and 10% attenuation depths (Z). ^ Three optically distinct regions of UV, but not PAR, attenuation were identified in Narragansett Bay, Rhode Island (USA). Seasonally, K values were highest in summer and lowest in winter. Variation in K dUV was a negative, linear function of salinity suggesting that quasi- conservative constituents (e.g., DOM) primarily determined UV attenuation. The Z10% for Kd305 (index of biologically damaging UV levels) was <1 m. In the tropical Pacific>(0°, 140° W; 15° N, 149° W) penetration of UV and PAR co-varied. Average K 0°–6° N were higher than values 9°–15° N and Z10% for Kd305 were 16 and 20 m, respectively. K correlated with patterns in chlorophyll a and beam attenuation, indicating that phytoplankton biomass (including population related DOM and POM) controlled UV and PAR attenuation. Phytoplankton in Narragansett Bay are unlikely to be affected by increases in the flux of UVB due to stratospheric ozone depletion while populations in the tropical and subtropical waters of the Pacific are presently UV stressed. ^ The effects of UVB, UVA, and PAR were investigated in desktop iron limitation experiments with Pacific phytoplankton. Phytoplankton exposed to full spectrum sunlight had a 20% greater decrease in PSII photochemistry. UV was also shown to negatively affect growth of Synechococcus spp. Effects were mainly due to UVA, but were intensified by UVB. Iron clearly stimulated growth and photosynthesis, but did not result in the radical shifts to larger species that have been consistently observed in similar container experiments that exclude UV. ^

Subject Area

Biology, Oceanography|Biology, Plant Physiology

Recommended Citation

Jennifer Eileen Prentice, "Solar ultraviolet radiation in the sea and photoinhibitory effects on natural phytoplankton populations" (1999). Dissertations and Master's Theses (Campus Access). Paper AAI9960032.
http://digitalcommons.uri.edu/dissertations/AAI9960032

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