Composition and spatio-temporal variability of particle fluxes in the Western Alboran Gyre, Mediterranean Sea

Abstract

Total mass and main constituents (carbonate, organic matter, biogenic opal and lithogenic fraction) flux series were obtained in the northern part of the Western Alboran Gyre during an annual cycle from July 1997 to May 1998, at 10 days sampling interval. Two mooring lines equipped with sediment trap–current meter pairs were deployed across the continental slope off Malaga. CTD, SeaWiFS and watershed fluvial discharge data sets were also obtained from several sources to establish their relations with particle flux data. Time-averaged fluxes for the whole period, including fluxes of organic carbon, increased slightly with depth in both locations as the result of the input of particulate matter by near-bottom nepheloid layers. Furthermore, time-averaged fluxes at mid waters were higher in the centre of the gyre than at its periphery, suggesting some kind of particle funnelling from the gyre periphery towards its centre. Temporal evolution of fluxes was highly variable throughout the year. All series showed an overall common evolution with a first peak at the beginning of summer 1997, a second broad composite peak during late autumn/winter and a third one in spring 1998. Composition of settling particles showed that summer and spring peaks were richer in biogenic constituents compared to the late autumn/winter peak. Particle fluxes to mid water depths in the northern part of the Alboran Sea seem to be mainly controlled by fluvial discharge and primary production. Fluvial discharge could be responsible for the higher lithogenic flux during autumn and winter, while high primary production could play a key role in generating biogenic particles during spring and summer. Regarding near-bottom fluxes, the temporal evolution was controlled both by the downward transfer of particulate matter from mid waters and the advective input of mostly lithogenic and carbonate matter. The increased advective input during maximum near-bottom fluxes is tentatively related to intense eddy-like activity recorded in the deep-water masses.