Input of various chemicals transported by Saharan dust and depositing at the sea surface in the Mediterranean sea

This paper reviews work on the role of Saharan dust as a contribution of various chemical to the Mediterranean basin. Both the magnitude and the mineralogical composition of atmospheric dust inputs indicate that eolian deposition is an important (50%) or even dominant (>80%) contribution to sediments in the offshore waters of the entire Mediterranean basin. The Mediterranean Sea is a semi-enclosed basin, that receives substances sporadically from the arid region of the Sahara desert. We considered the location and strength of source areas, the transport paths of material away from the desert, the number of Saharan dust transports per year, the way to be dust is deposited (wet and dry mode), the fluxes of Saharan dust, the nature of the material, and the contribution of nutrients to the sea surface. Estimates of atmospheric inputs to the Mediterranean and some coastal areas are reviewed. Model data for nutrients indicate that the atmosphere delivers the nitrogen and one-third of total phosphorus to the entire basin. Measured data in sub-basins, such as the Western Mediterranean and Eastern Mediterranean indicate an even greater proportions of atmospheric versus riverine input. New production supported by atmospheric nitrogen deposition ranges from 2–4 g C m -2 yr -1 , whereas atmospheric phosphorus deposition appears to support less than 1 g C m -2 yr -1 . In spite of the apparently small contribution of atmospheric deposition to overall production in the basin it has been suggested that certain episodic phytoplankton blooms are triggered by atmospheric deposition of N, P or Fe. Iron fluxes may be important in determining the nature and quantity of carbon fluxes from Fe-rich areas (like MED Sea), in addition to Fe-poor areas such as the extant Southern Ocean. A geophysiological model shows that iron removal from the photic zone does occur at a much higher rate than the conventional biological pump can account for and that this might release the risk of excessive phosphate scavenging.