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 chromophoric (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 normalized 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 correlated with salinity (r = −0.95) and sigma-t (r = −0.99). These strong linear relationships can be used as a tool for monitoring surface circulation and salinity in these coastal waters. The relationships between CDOM absorption and fluorescence were also characterized in the UV and visible regions. In the UV region, the observed relationship was found to be consistent with previously published results. In the visible region a relationship was found that was different from that in the UV. Our results therefore support the possibility of using fluorescence characteristics for extensive monitoring of CDOM in coastal waters strongly influenced by freshwater runoff. Such relationships may prove useful for remote sensing to correct chla values and the large-scale modelling of primary production in coastal waters.