ALBERT

Beschreibung: Simultaneous measurements of atmospheric deposition and of sinking particles at 200 m depth, were performed in the Ligurian Sea (North-Western Mediterranean) between 2003 and 2007 along with the historical time records of phytoplanktonic activity from satellite images. Atmospheric deposition of Saharan dust particles was very irregular and confirmed the importance of sporadic high magnitude events over the annual average (11.4 g m−2 yr−1 for the 4 yr). The average marine total mass flux was 31 g m−2 yr−1, the larger fraction being the lithogenic one (~37%). The marine total mass flux displayed a seasonal pattern with a maximum in winter occurring before the onset of the spring bloom. The highest POC fluxes did not occur during the spring bloom nor could they be related to any noticeable increase in the surface phytoplanktonic activity. Over the 4 yr of the study, the strongest POC fluxes were concomitant with large increases of the lithogenic marine flux, which had originated from either recent Saharan fallout events (February 2004, August 2005), or from ''old'' Saharan dust ''stored'' in the upper water column layer (March 2003, February 2005), or alternatively from lithogenic material originating from Ligurian riverine flooding (December 2003, Arno, Roya and Var rivers). These ''lithogenic events'' are believed to result from a combination of physical processes (winter mixing), the aggregation of faecal pellets resulting from zooplankton activity, and also organic-mineral aggregation inducing a ballast effect. However, such an event also occurred in August 2005 without any physical mixing, and was attributed to Saharan dust-induced biological enhancement. POC export provoked by the simultaneous occurrence of winter mixing and an extreme dust event (February 2004, 22 g m−2 deposition) was shown to represent 50% of the total annual POC export at 200 m in the water column that year, as compared to only ~25% for the bloom period. This indicates the importance of atmospheric deposition for POC fluxes in the Mediterranean Sea, which is an area strongly influenced by Saharan dust inputs.