Saharan wet deposition: An external source of trace metals in the Mediterranean Sea

Trace metals are known to inhibit or increase phytoplankton growth and modify phytoplankton community structure. As for iron and nutrients, the atmospheric fluxes of metals could constitute a major source for surface ocean.  However, until now, no in-situ observations have been able to support this assumption. This was done by international ProcEss studies at the Air-sEa Interface after dust deposition in the MEditerranean sea (PEACETIME) team in using an original strategy where the rain events were tracked during cruise in the Mediterranean to obtain concurrent measurements of metal concentrations in the atmospheric depositions and in the water column before and after the rains, as described in Desboeufs et al.. The authors show that after an intense Saharan wet deposition events, the atmospheric inputs can double, or even increase by a factor of 10, the dissolved marine stocks of metals (iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), copper (Cu), Lead (Pb)). In a context where climate models predict both increasing of Saharan dust deposition in the Mediterranean, these results suggest the key role of Saharan inputs in the future marine biogeochemical processes in this region. The authors recommend to develop the used approach in other parts of the world to explore the role of atmospheric deposition.

Reference : Desboeufs, K., Fu, F., Bressac, M., et al. (2022). Wet deposition in the remote western and central Mediterranean as a source of trace metals to surface seawater. Atmos. Chem. Phys., 22, 2309–2332. https://doi.org/10.5194/acp-22-2309-2022