MEASUREMENT OF SOLAR-STIMULATED FLUORESCENCE IN NATURAL-WATERS

The oceanic Fraunhofer line discriminator (OFLD), designed to measure the solar-stimulated inelastic scattering in the ocean, has been deplo yed in various types of water in Florida Bay and the Dry Tortugas to m easure Fraunhofer lines and oxygen-absorption lines near 689 nm in the solar spectrum. The line-filling principle and previous work enable u s to partition the measured light into elastic, Raman scattering, and fluorescence components. We show that in optically deep, oligotrophic water, where chlorophyll a (Chl a) concentration is as low as 0.1 mg m (-3), fluorescence near 689 nm was still measurable by the OFLD. In mo derately eutrophic shallow waters, where Chi a concentration ranges fr om 0.2 to 0.8 mg m(-3), the fluorescence from either Chi a or dissolve d organic matter in the water column was found to be a negligible comp onent of the total light field due to the additional light reflected f rom the bottom. We also include measurements of the solar-stimulated f luorescence for benthic surfaces, such as brain coral, and have found these to be saturated under normal solar illumination.