Vertical distribution and temporal variation of dissolved organic carbon in the North-Western Mediterranean Sea

Abstract

During 1991 and 1992, detailed vertical profiles of dissolved organic carbon (DOC) content were obtained monthly, in the North-Western Mediterranean at the DYFAMED-1 site (43°25′N, 07°52′E). DOC was measured using a high temperature catalytic oxidation method. In the 150–2000 m layer, DOC distribution was quite uniform, with a content of about 0.6–0.7 mg C l −1. In surface waters, DOC concentration changed according to hydrological situation and primary production cycle. During February, waters were DOC-homogeneous through the whole water column; then surface concentrations increased until autumn with maxima of about 1.1–1.2 mg C l −1 between 0 and 50 m depths. Assuming that the DOC is continuously removed from surface waters by diffusive processes during the stratified period and that the DOC accumulated in surface waters until the end of autumn is removed by advection during the short period of winter deep water formation, we find that an amount of 18.4 g Cm −2y −1 is transferred to the deep layer. This value is more than twice the particulate organic carbon flux measured on sediment traps (4–7 g Cm −2 y −1), but agrees with published new production values.