Fluorescence and DOC contents of pore waters from coastal and deep-sea sediments in the Gulf of Biscay

Abstract Fluorescence of waters from the Gulf of Biscay was investigated. Pore waters fluoresced more intensely and exhibited red-shifted spectra relative to overlying seawaters. Also, a blue-shift was observed going from coastal to open sea sites. Results indicate that continental inputs of fluorescent material reach the sea bed at all sites studied. Organic matter (OM) modifications within sediments were also observed. In the uppermost layer (6 cm), fluorescence intensity and dissolved organic carbon (DOC) concentrations decrease, followed by a red-shift in emission spectra with increasing depth. This may reflect the increase in OM molar mass due to humification. The reverse of these trends in the deepest sub-oxic sediments might be related to the degradation of OM released from the solid phase, resulting in dissolved fluorescent material with a relative paucity of oxygen-containing functional groups. A very good correlation of DOC with fluorescence was observed in all cores.