Carbon inputs of the Rhone River to the Mediterranean Sea: Biogeochemical implications

Since the damming of the Nile, the Rhone River is the main freshwater and s ediment supplier to the Mediterranean Sea. We estimated for the period 1987 -1996, the dissolved and particulate organic carbon (DOC and POC), dissolve d inorganic carbon (DIC), and total suspended matter (TSM) fluxes of the Rh one River to the Mediterranean Sea to be 1.1 +/- 0.2, 1.6 +/- 0.5, 16.2 +/- 0.3 x 10(10) moles C yr(-1), and 9.9 +/- 6.4 x 10(6) t yr(-1), respectivel y. PIC flux was estimated to be 8.2 +/- 5.4 x 10(9) moles C yr(-1). On the basis of literature data, we estimated that nearshore bacterial respiration of Rhone derived labile-POC and -DOC (LPOC and LDOC) might produce in a fe w days similar to 0.21 and 0.12 x 10(10) moles CO2 yr(-1), respectively. Ex tended to the whole Mediterranean, this study suggests that bacterial respi ration of labile organic carbon derived from Mediterranean rivers might rap idly (days) produce 2.6-11 x 10(10) moles CO2 yr(-1). On the continental sh elf, up to 4.7 x 10(10) moles of organic carbon introduced by primary produ ction and Rhone export would escape each year to sedimentation and bacteria l mineralization and would be exported off the shelf. Moreover, as total ca rbon fixed by phytoplankton exceeds (+ 5.2 x 10(10) moles C yr(-1)) the CO2 produced by bacterial respiration ton average), the biological system on t he shelf, could be considered as an autotrophic system and then a sink for atmospheric CO2. However, these numbers need further examination because of the large uncertainties associated currently to the bacterial growth effic iency values (+ 100%).