Miquel, J.C., Cochran, J.K., Gasser, B., Rodriguez y Baena, A.M., Peterson, M., Fowler, S.W., Lee, C., Masqué, P., Jeandel, C., and Marty, J.C. CARBON EXPORT IN THE NW MEDITERRANEAN DERIVED FROM MOORED SEDIMENT TRAPS AND TH-234:U-238 DISEQUILIBRIA; RESULTS FROM THE BARMED, DYFAMED AND MEDFLUX STUDIES

Abstract: Downward flux of particulate material and associated carbon export plays a key role in the sequestration of CO2 from ocean upper waters and in the biogeochemical cycle of many elements. Historically, fluxes have been measured using sediment traps but, in the last 15 years, several studies have shown possible bias in trap data (mostly related to hydrodynamic effects) and proposed the use of radionuclides, particularly the disequilibria between the natural radionuclide Th-234 and its parent U-238, as a complementary approach to vertical flux assessment. In the central Ligurian Sea (NW Mediterranean) open waters, vertical fluxes are regularly monitored with Technicap-PPS5 sediment traps (DYFAMED time-series). Furthermore, in 2003, fluxes were measured using IRS sediment traps (MEDFLUX) and the water column sampled several times in spring and summer (BARMED and MEDFLUX projects). POC fluxes were also derived from the Th-234 deficit as compared to U-238 in the water column and the POC/Th-234 ratio in sinking particles. POC fluxes clearly decreased after a relative short but intense spring peak and the change in carbon export was followed by the several methodological approaches reported.