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 an offshore-onshore transect from the oligotrophic blue waters of the western Sargasso Sea to the eutrophic waters of lower Delaware Bay. Low values of the ratio of variable to maximum fluorescence (F(v)/F(m)) of dark adapted samples provided evidence for reduced quantum efficiences in surface waters (z = 10 m) of the Sargasso Sea. In contrast, higher 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) observed over the continental shelf. Variations of F(v)/F(m) in surface samples (5 or 10 m depth) were associated with changes in hydrographic features that were consistent with the hypothesis that reduced values of phi(II) in Sargasso Sea surface waters were due to nutrient limitation of phytoplankton photosynthetic energy conversion. In contrast, F(v)/F(m) of samples collected from the chlorophyll maximum layer were independent of distance from shore and water mass characteristics.