LIGHT-ABSORPTION AND FLUORESCENCE PROPERTIES OF CHROMOPHORIC DISSOLVED ORGANIC-MATTER (CDOM), IN THE ST-LAWRENCE ESTUARY (CASE 2 WATERS)

The absorption coefficient and the fluorescence emission of chromophor ic (coloured) dissolved organic matter (CDOM) were determined along a 1200 km transect in the Estuary and Gulf of St. Lawrence. Fluorescence spectra were spectrally corrected against a reference standard and no rmalized to the water Raman signal to provide results in Raman units. Because CDOM originates mainly from freshwater river runoff in the St. Lawrence system, its optical properties were found to be inversely co rrelated with salinity (r = -0.95) and sigma-t (r = -0.99). These stro ng linear relationships can be used as a tool for monitoring surface c irculation and salinity in these coastal waters. The relationships bet ween CDOM absorption and fluorescence were also characterized in the U V and visible regions. In the UV region, the observed relationship was found to be consistent with previously published results. In the visi ble region a relationship was found that was different from that in th e UV. Our results therefore support the possibility of using fluoresce nce characteristics for extensive monitoring of CDOM in coastal waters strongly influenced by freshwater runoff. Such relationships may prov e useful for remote sensing to correct chi a values and the large-scal e modelling of primary production in coastal waters. Copyright (C) 199 6 Elsevier Science Ltd