Particulate fluxes of organic compounds and their relationship to zooplankton fecal pellets in the northwestern Mediterranean Sea

Abstract

Abstract Sediment trap experiments were conducted in the northwestern Mediterranean (Ligurian sea) in 1987 in the course of the Dyfamed project. The particles collected during 9–15 day intervals from February through July at 200 m and from April through May at 2000 m depth were analysed for organic carbon, nitrogen, fatty acids and n-alkanes. Concentrations in these particles were compared to those in freshly-produced zooplankton fecal pellets collected from several cruises during the same period. In winter, high mass fluxes were encountered at 200 m; the organic material was characterized by a relatively high proportion of n-alkanes and C24 fatty acid which are characteristic of refractory (old) organic matter and a low content of the more labile fatty acids. During the spring and summer period, fluxes contained undegraded phytoplankton and zooplankton material. In the 2000 m trap samples, refractory organic matter was still present, but the fresh input was very low and had evidently been consumed in the upper water column. There was no tendency toward a higher content in bacterial fatty acid markers in zooplankton fecal pellets and 200 m sediment trap material. Based on the assumption that all n-alkanes in trap collections originate from sinking fecal pellets, end-member calculations indicate that intact zooplankton fecal pellets are important contributors to vertical particulate fluxes at 200 m. The maximum contribution is estimated to be between 10% (in summer) and 30% (spring) using n-alkane marker concentrations.