Behavior of natural fluorescence in Sagami Bay and Tokyo Bay, Japan — vertical and lateral distributions

Abstract

The vertical distribution of natural fluorescence was investigated at one location in Sagami Bay, Japan. Natural fluorescence showed low values in surface seawater, increasing with depth. Linear relations were observed between natural fluorescence and nutrients, such as phosphate and nitrate. It is suggested that natural fluorescence resulting from marine humic substances can behave in a manner similar to phosphate and nitrate in the water column. Linear relations with negative slopes were found between salinity and natural fluorescence at several locations in Tokyo Bay, Japan. This indicates that natural fluorescence in this area results from terrestrial humic substances and is dispersed mainly by mixing of water masses. Fluorescence and absorption spectra of the seawater in Tokyo Bay showed spectra similar to sedimentary fulvic acid from Tokyo Bay. Fluorescence/absorbance ratios were nearly constant for the seawater samples in Tokyo Bay.