Composition and temporal variability of particle fluxes in an insular canyon of the northwestern Mediterranean Sea

摘要

Particle fluxes have been widely studied in canyons located in continental margins; conversely, particle fluxes in canyons in sediment starved margins incising small island margins have received very little attention and remain poorly understood. The Menorca Canyon is the largest canyon system in the Balearic Archipelago. Despite the high oligotrophic conditions of the Balearic Archipelago the canyon and surrounding areas host diverse communities dominated by benthic suspension feeders. Understanding the magnitude and variability of environmental factors influencing these communities thus remain crucial. In order to characterize the temporal variability of particle fluxes, analyze its geochemical and macroscopic composition and identify the main processes that modulate particle fluxes in the Menorca Canyon, one instrumented line with a sediment trap and a current meter was deployed at 430 m water depth from September 2010 to October 2012. Particle fluxes ranged between 190 and 2300 mg m(2)d(-1) being one of the lowest ever registered in a Mediterranean submarine canyon's head. The CaCO3 fraction was the major constituent contrasting with the general trend observed in other Mediterranean canyons. Macroscopic constituents (fecal pellets, Posidonia oceanica detritus and pelagic and benthic foraminifera) presented a wide variability throughout the sampling period and were not significantly correlated with the total mass flux. The low magnitude of the registered fluxes and the lack of correlation with the observed environmental variables (e.g., currents, winds, wave height, chlorophyll-a biomass) suggest that there is no evident controlling mechanism. However, we could infer that resuspension processes and the presence of different hydrodynamic features (e.g., eddies, interchange of water masses) condition the magnitude and composition of particle fluxes.