Search

An experiment was carried out in the Gulf of Lions (NW Mediterranean) in February 2014 to assess the temporal and spatial variability of the distribution and size of suspended particulate matter (SPM) in the Rhône Region of Freshwater Influence (ROFI). A set of observations from an autonomous underwater glider, satellite ocean color data, and meteorological and hydrological time-series data highlighted the high variability of the Rhône River surface turbid plume and presence of a bottom nepheloid layer (BNL) that depended on wind and river discharge conditions. While continental winds pushed the surface plume offshore, marine winds pressed the plume at the coast and favored the sedimentation of as well as nourishment of the BNL. Moderate storm events favored breakage of the plume stratification and along-shelf transport of Rhône River particles. The spectral slopes of glider and satellite-derived light backscattering coefficients, γ, were used as a proxies of the SPM size distribution. The results clearly showed that the change of the SPM size in the nepheloid layers was induced by the flocculation of fine sediments, which became finer seaward throughout the ROFI, as well as the effect of rough weather in the breakup of flocs. [ABSTRACT FROM AUTHOR]

An innovative experiment was carried out in the vicinity of the Rhône River mouth in February 2014. An instrumental package, composed of a CTD, a LISST-100 type B (1.25–250 μm), and a LISST-HOLO (20–2000 μm), was used to characterize the hydrological parameters and suspended particles properties (concentration, size, composition, shape, and effective density) in the region of freshwater influence (ROFI) of the Rhône River. Besides, a coastal SLOCUM glider, equipped with a CTD and optical backscattering sensors at several wavelengths, was deployed to detail the spatial description of the hydrological parameters and some particle properties. Large river discharge (annual flood ~ 5000 m 3 s − 1 ) and strong wind conditions favored the dispersal of the river plume on the shelf. Surface suspended particulate matter concentrations decreased rapidly seaward from 20 mg L − 1 next to the river mouth to 1.5 mg L − 1 at the shelf break. A persistent bottom nepheloid layer was observed across the shelf with concentrations decreasing from 8 mg L − 1 at the coast to 1 mg L − 1 at the shelf break. Observations showed that most of suspended particles were mainly flocculated in micro and macro-flocs (30–400 μm) in inner-shelf waters. The particle assemblage in the Rhône River plume and in the bottom nepheloid layer became progressively finer seaward and the associated effective density increased from 370 to 1600 kg m − 3 . Outside the plume, planktonic organisms increasingly contributed to the total volume concentration. Finally, we demonstrated the ability of gliders, equipped with optical backscattering sensors at several wavelengths, to describe the fine scale distributions of suspended particles, and provide an index of their size distribution. [ABSTRACT FROM AUTHOR]