Miquel, Juan-Carlos¹, Scott W. Fowler¹, Jacques La Rosa¹ and Jean-Claude Marty²

¹IAEA - Marine Environment Laboratory, 4 Quai Antoine 1er, MC98000 Monaco, Tel: (377) 97977259, Fax (377) 97977273, E-mail: J.C.Miquel@iaea.org and ²Laboratoire Océanographique de Villefranche, BP 08, 06238 Villefranche sur Mer Cédex, France,

Seasonal and interannual dynamics of the downward flux of carbon in the open NW Mediterranean Sea during the JGOFS era

Since 1987, downward flux of particles, carbon and other major elements have been studied at 200 and 1000m depths at the DYFAMED station in the open Mediterranean Sea (43° 25' N, 7° 52' E). At this reference site the biogeochemical regime varies from mesotrophic in spring (phytoplankton biomass dominated by diatoms and nanoflagellates) to oligotrophic during summer/fall (with increasing importance of picoplankton) before the winter mixing. Furthermore, advection is low and processes can be studied on a 1D vertical scale. Particulate fluxes displayed a marked seasonal pattern with highest fluxes found during winter and spring. Organic carbon fluxes showed the same pattern with the highest fluxes occurring normally in late spring. The average total carbon flux measured over a decade was 4.0 g m^-2 a^-1 at 200 m depth, with a mean organic carbon flux of 2.9 g m^-2 a^-1. Pigments and fecal pellet fluxes also displayed strong seasonal variability and were major contributors to POC export. Annual primary production measured by the ¹⁴C method varied between 86-232 g C m^-2 a^-1 indicating that the directly measured POC flux was only a small fraction of the total carbon production in the euphotic zone. However, the particulate fluxes appear to be a major source of organic material delivered to the deeper layers during several months of the year.