Excitation-emission-matrix fluorescence spectroscopy applied to humic acid bands in coral reefs

An investigation of the three-dimensional excitation-emission-matrix (EEM) fluorescence spectra of humic acids and other organic matter from corals and other sources is reported, the results of which have implications for the use of corals as paleoenvironmental indicators. Four characteristic excitation/emission peaks were identified in the samples studied, at 310/430, 340/450, 390/490 and 280/(320-350) nm, the last of these attributed to protein fluorescence. The positions of these peaks were essentially invariant between different samples, including coral extracts, solid corals, seawater, and commercially-available humic acids, although their relative intensities showed considerable variation. The use of the EEM technique in the present work has demonstrated that changes in sample concentration can considerably change the intensity distribution of the fluorescence spectra, particularly if strongly absorbant, non-fluorescent species are present. Comparison of the EEM spectra of organic matter extracted from bright and dull coral bands showed the spectroscopic structure of the fluorescence emitted to be essentially identical for both bands; the emissions appear to differ only in their absolute intensities.