Effects of a plume front on the distribution of inorganic and organic matter off the Rhône River

Abstract

Hydrological and chemical structures off the Rhône River estuary resulting from the introduction of the river flow into the Mediterranean Sea are described. The effect of the fresh-water/sea-water interface on the distribution of inorganic and organic matter off the Rhône river is investigated. Strong vertical gradients of inorganic and dissolved organic matter such as lipids characterized the first few meters in this area (from 83.7 to 0.6 N-NO₃ µgat l⁻¹, from 6.39 to 0.92 N-NH₄ µgat l⁻¹ and from 299 to 73 µg l⁻¹ of total dissolved lipids). At the interface, substantial increases of particulate organic (PON: from 45 µg l⁻¹ at surface to 118 µg l⁻¹ at the interface, POC: from 462 to 876 µg l⁻¹, total particulate lipids: from 33 to 648 µg l⁻¹) and suspended matter in general (from 18 to 22.2 mg l⁻¹) were observed. High phytoplanktonic production may account for some of this enrichment, although passive accumulation might also be involved.