Evaluation of the dust deposition fluxes to the oceans
To assess the potential impact of nutrient inputs associated with the deposition of mineral aerosols on the functioning of marine ecosystems, it is imperative to quantify the deposition fluxes with high spatial and temporal variability. Thus an intense event of desert aerosol deposit can occur on only a few days but it can constitute a significant fraction (~1/3) of the annual total deposition.
Currently, deposition fluxes simulated by the 3D models of the atmospheric cycle of desert aerosols are under-constrained, mainly due to the lack of observations for comparison purposes. We are therefore implementing continuous measurements of deposition fluxes that meet best the episodic character of the deposition of desert aerosols.
These measurements consists both in the determination of the deposited masses as much as possible in combination with more complete measurements of the composition of the particulate and aqueous phases. Several stations have been deployed in the Mediterranean, in the framework of the DEMO program and in coordination with the CHARMEX program and also in South Hemisphere at Kerguelen (FLATOCOA program) and Patagonia. The aim for the Mediterranean basin is to (1) describe the evolution of mass flux with respect to the distance to the North African continent and the regional distribution of precipitations (2) assess the influence of the composition of precipitations on the solubility of aerosols in selected stations and/or periods and (3) assess the relative contribution of desert aerosols in terms of intake of nutrients compared to that of anthropogenic aerosols.. In the South Hemisphere, the aim is to measure the dynamic of deposition fluxes over the South Indian Ocean and the chemical properties of the aerosol exported from Patagonia. These data will be used also as constraints for the regional simulation of deposition fluxes by 3D models of the mineral dust cycle in order to increase their reliability and their capability to foreseen mineral dust cycle evolution induced by climatic changes.
Diagram of the network of measurement of the deposit of aerosols proposed in CHARMEX. The chemical composition of soluble and insoluble fractions of deposition samples will be determined on the super sites; the measurements of the flows of mass deposit will be conducted through an automatic collector "CARAGA" (link?) on super sites and secondary site.