Fluorescent matter in the eastern Atlantic Ocean. Part 2: vertical profiles and relation to water masses

Water samples taken at seven stations in the eastern Atlantic Ocean were fluorometrically analyzed. Vertical profiles describe the distribution of gelbstoff and of tyrosine-like and tryptophan like molecules. These are compared with hydrographic data. Gelbstoff fluorescence is low near the sea surface due to photodegradation. Except for enhanced values at 300–500 m depth at some stations, Gelbstoff fluorescence is almost constant in intermediate (Mediterranean Water, Antarctic Intermediate Water) and deep waters (North Atlantic Deep Water) despite the very different origins of these water masses. trast to gelbstoff, tryptophan- and tyrosine-like signals are highest near the sea surface. Particulate organic matter and derived dissolved organic molecules are discussed as possible sources of these fluorophores. In the upper portion of the main thermocline, where the gelbstoff is greater than deeper in the water column, the fluorescence signals of gelbstoff and tryptophan-like molecules covary. This supports the assumption that decomposition of sinking particles, and increased concentrations of bacteria due to this process, contribute to the vertical distribution of fluorescent matter at these depths.