FLUORESCENCE ASSESSMENT OF THE MAXIMUM QUANTUM EFFICIENCY OF PHOTOSYNTHESIS IN THE WESTERN NORTH-ATLANTIC

The maximum quantum efficiency (phi(II)) of phytoplankton photosystem II photochemistry was assessed using a pump and probe fluorometer on a n offshore-onshore transect from the oligotrophic blue waters of the w estern Sargasso Sea to the eutrophic waters of lower Delaware Bay. Low values of the ratio of variable to maximum fluorescence (F(v)/F(m)) o f dark adapted samples provided evidence for reduced quantum efficienc es in surface waters (z = 10 m) of the Sargasso Sea. In contrast, high er values of F(v)/F(m) in estuarine samples indicated near maximal phi (II) in lower Delaware Bay, with intermediate values of F(v)/F(m) obse rved over the continental shelf. Variations of F(v)/F(m) in surface sa mples (5 or 10 m depth) were associated with changes in hydrographic f eatures that were consistent with the hypothesis that reduced values o f phi(II) in Sargasso Sea surface waters were due to nutrient limitati on of phytoplankton photosynthetic energy conversion. In contrast, F(v )/F(m) of samples collected from the chlorophyll maximum layer were in dependent of distance from shore and water mass characteristics.