SPATIAL VARIABILITY OF OCEANIC PHYCOERYTHRIN SPECTRAL TYPES DERIVED FROM AIRBORNE LASER-INDUCED FLUORESCENCE EMISSIONS

We report spatial variability of oceanic phycoerythrin spectral types detected by means of a blue spectral shift in airborne laser-induced f luorescence emission. The blue shift of the phycoerythrobilin fluoresc ence is known from laboratory studies to be induced by phycourobilin c hromophore substitution at phycoerythrobilin chromophore sites in some strains of phycoerythrin-containing marine cyanobacteria. The airborn e 532-nm laser-induced phycoerythrin fluorescence of the upper oceanic volume showed distinct segregation of cyanobacterial chromophore type s in a flight transect from coastal water to the Sargasso Sea in the w estern North Atlantic. High phycourobilin levels were restricted to th e oceanic (oligotrophic) end of the flight transect, in agreement with historical ship findings. These remotely observed phycoerythrin spect ral fluorescence shifts have the potential to permit rapid, wide-area studies of the spatial variability of spectrally distinct cyanobacteri a, especially across interfacial regions of coastal and oceanic water masses. Airborne laser-induced phytoplankton spectral fluorescence obs ervations also further the development of satellite algorithms for pas sive detection of phytoplankton pigments. Optical modifications to the NASA Airborne Oceanographic Lidar are briefly described that permitte d observation of the fluorescence spectral shifts. (C) 1998 Optical So ciety of America.