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International audience; A method is described for field measurements of size-resolved aerosol vertical fluxes over rural areas. The method is based on a direct eddy covariance method and using an Electrical Low-Pressure Impactor (Outdoor ELPI). The main advantage of this method is to measure simultaneously the aerosol vertical fluxes at several submicron sizes. Due to the low response time of the experimental setup (about 1 s) compared to the turbulent time scales of the particle concentrations, a flux correction was applied and it is based on spectral analysis. As an example of results, the particles fluxes normalized by the concentration were measured over a maize field for atmospheric aerosols that ranged in size from 0.007 to 1.6 mm.

This paper analyzes the relationship between deep sedimentary fluxes and ocean current vertical velocities in an offshore area of the Ionian Sea, the deepest basin of the Eastern Mediterranean Sea. Sediment trap data are collected at 500 m and 2800 m depth in two successive moorings covering the period September 1999–May 2001. A tight coupling is observed between the upper and deep traps and the estimated particle sinking rates are higher than 200 m day−1. The current vertical velocity field is computed from a high resolution Ocean General Circulation Model simulation and from the wind stress curl. Current vertical velocities are larger and more variable than Ekman vertical velocities, yet the general patterns are alike. Current vertical velocities are generally smaller than 1 m day−1: we therefore exclude a direct effect of downward velocities in determining high sedimentation rates. However, we find that upward velocities in the subsurface layers of the water column are positively correlated with deep particle fluxes. We thus hypothesize that upwelling would produce an increase in upper ocean nutrient levels – thus stimulating primary production and grazing – a few weeks before an enhanced vertical flux is found in the sediment traps. By analyzing the delayed effects of ocean vertical velocities on deep particle fluxes we envisage a spectrum of particle sinking speeds ranging from about 100 m day−1 to more than 200 m day−1. High particle sedimentation rates may be attained by means of rapidly sinking fecal pellets produced by gelatinous macro-zooplankton. Other sedimentation mechanisms, such as dust deposition, are also considered in explaining large pulses of deep particle fluxes. The fast sinking rates estimated in this study might be an evidence of the efficiency of the biological pump in sequestering organic carbon from the surface layers of the deep Eastern Mediterranean basins.