Seasonal variability of the advective transport of particulate matter and organic carbon in the Gulf of Lion (NW Mediterranean)

Nine hydrographic cruises were performed on the Gulf of Lion continental ma rgin between June 1993 and July 1996. These observations are analysed to qu antify the fluxes of particulate matter and organic carbon transported alon g the slope by the Northern Current and to characterise their seasonal vari ability. Concentration of particulate matter and organic carbon are derived from light-transmission data and water sample analyses. The circulation is estimated from the geostrophic current field. The uncertainty on the trans port estimate, related to the error on the prediction of particle concentra tions from light-transmission data and the error on velocities, is assessed . The particulate matter inflow entering the Gulf of Lion off Marseille is comparable to the Rhone River input and varies seasonally with a maximum tr ansport between autumn and spring. These modifications result from variatio ns of the water flux rather than Variations of the particulate matter conce ntration. Residual transports of particulate matter and organic carbon acro ss the entire Gulf of Lion are calculated for two cruises enclosing the dom ain that were performed in February 1995 and July 1996. The particulate mat ter budgets indicate a larger export from the shelf to deep ocean in Februa ry 1995 (110 +/- 20 kg s(-1)) than in July 1996 (25 +/- 18 kg s(-1)). Likew ise, the mean particulate organic carbon export is 12.8 +/- 0.5 kg s(-1) in February 1995 and 0.8 +/- 0.2 kg s(-1) in July 1996. This winter increase is due to larger allochthonous and autochthonous inputs and also to enhance d shelf-slope exchange processes, in particular the cascading of cold water from the shelf. The export of particulate matter by the horizontal current s is moreover two orders of magnitude larger than the vertical particulate fluxes measured at the same time with sediment traps on the continental slo pe. (C) 2001 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.