BG Biogeosciences BG 1726-4189 Copernicus GmbH Göttingen, Germany 10.5194/bg-8-1067-2011 Longitudinal variability of the biogeochemical role of Mediterranean aerosols in the Mediterranean Sea Ternon E. 1 2 Guieu C. 1 2 Ridame C. 3 L'Helguen S. 4 Catala P. 5 6 Laboratoire d'Océanographie de Villefranche/Mer, UMR7093, INSU-CNRS – Observatoire Océanologique de Villefranche-sur-mer, Chemin du Lazaret, Villefranche sur Mer, France UPMC Université Paris 06, UMR7093, LOV, Observatoire Océanologique de Villefranche-sur-mer, Chemin du Lazaret, Villefranche sur Mer, France LOCEAN, UMR7159, Université Pierre et Marie Curie, Place Jussieu, Paris, France Laboratoire des Sciences de l'Environnement Marin, UMR6539, UBO/CNRS/IRD, IUEM, Place Nicolas Copernic, 29280 Plouzané, France UPMC Université Paris 06, UMR7621, LOMIC, Observatoire Océanologique, Avenue Fontaulé, 66650 Banyuls/mer, France LOMIC, UMR7621, CNRS – Observatoire Océanologique, Avenue Fontaulé, 66650 Banyuls/mer, France 05 05 2011 8 5 1067 1080 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.biogeosciences.net/8/1067/2011/bg-8-1067-2011.html The full text article is available as a PDF file from http://www.biogeosciences.net/8/1067/2011/bg-8-1067-2011.pdf

The Mediterranean Sea is a semi-enclosed basin characterized by a strong thermal stratification during summer during which the atmosphere is the main source of new nutrients to the nutrient-depleted surface layer. From aerosol sampling and microcosm experiments performed during the TransMed BOUM cruise (June–July 2008) we showed that: (i) the Mediterranean atmosphere composition (Al, Fe, P) was homogeneous over ~28° of longitude and was a mixture with a constant proportion of anthropogenic contribution and a variable but modest contribution of crustal aerosols. This quite stable composition over a one month period and a long transect (~2500 km) allowed to define the Mediterranean atmospheric "background" that characterizes the summer season in the absence of major Saharan event and forest fires, (ii) primary production significantly increased at all tested stations after aerosols addition collected on-board and after Saharan dust analog addition, indicating that both additions relieved on-going (co)-limitations. Although both additions significantly increased the N<sub>2</sub> fixation rates at the western station, diazotrophic activity remained very low (~0.2 nmol N L<sup>−1</sup> d<sup>−1</sup>), (iii) due to the presence of anthropogenic particles, the probable higher solubility of nutrients associated with mixed aerosols (crustal + anthropogenic contribution), conferred a higher fertilizing potential to on-board collected aerosol as compared to Saharan dust analog. Finally, those experiments showed that atmospheric inputs from a mixed atmospheric event ("summer rain" type) or from a high-intensity Saharan event would induce comparable response by the biota in the stratified Mediterranean SML, during summer.

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