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Volume 17, issue 23 | Copyright

Special issue: CHemistry and AeRosols Mediterranean EXperiments (ChArMEx)...

Atmos. Chem. Phys., 17, 14645-14660, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Dec 2017

Research article | 08 Dec 2017

Primary marine aerosol physical flux and chemical composition during a nutrient enrichment experiment in mesocosms in the Mediterranean Sea

Allison N. Schwier1, Karine Sellegri1, Sébastien Mas2, Bruno Charrière3,7, Jorge Pey4,a, Clémence Rose1, Brice Temime-Roussel4, Jean-Luc Jaffrezo5, David Parin2, David Picard1, Mickael Ribeiro1, Greg Roberts6, Richard Sempéré7, Nicolas Marchand4, and Barbara D'Anna8,b Allison N. Schwier et al.
  • 1Laboratoire de Météorologie Physique CNRS UMR6016, Observatoire de Physique du Globe de Clermont-Ferrand, Université Blaise Pascal, 63171 Aubière, France
  • 2Centre d'écologie marine expérimentale MEDIMEER, UMS3282 OSU OREME, Université de Montpellier, CNRS/IRD, Sète, France
  • 3Centre de Formation et de Recherche sur les Environnements Méditerranéens CNRS UMR5110, Université de Perpignan Via Domitia, 66860 Perpignan, France
  • 4Aix Marseille Univ., CNRS, LCE, Marseille, France
  • 5Univ. Grenoble Alpes, CNRS, IRD, IGE, 38000 Grenoble, France
  • 6Centre National de Recherches Météorologiques (CNRM), Météo-France, Toulouse, France
  • 7Aix-Marseille Université, Mediterranean Institute of Oceanography (MIO), CNRS/IRD, Université de Toulon, UM 110, 13288 Marseille, France
  • 8Institut de Recherches Sur la Catalyse et l'Environnement de Lyon CNRS UMR5256, Université Claude Bernard Lyon 1, 69626 Villeurbanne, France
  • anow at: Geological Survey of Spain (IGME), 50006 Zaragoza, Spain
  • bnow at: Aix Marseille Univ., CNRS, LCE, Marseille, France

Abstract. While primary marine aerosol (PMA) is an important part of global aerosol total emissions, its chemical composition and physical flux as a function of the biogeochemical properties of the seawater still remain highly uncharacterized due to the multiplicity of physical, chemical and biological parameters that are involved in the emission process. Here, two nutrient-enriched mesocosms and one control mesocosm, both filled with Mediterranean seawater, were studied over a 3-week period. PMA generated from the mesocosm waters were characterized in term of chemical composition, size distribution and size-segregated cloud condensation nuclei (CCN), as a function of the seawater chlorophyll a (Chl a) concentration, pigment composition, virus and bacteria abundances. The aerosol number size distribution flux was primarily affected by the seawater temperature and did not vary significantly from one mesocosm to the other. The aerosol number size distribution flux was primarily affected by the seawater temperature and did not vary significantly from one mesocosm to the other. Particle number and CCN aerosol fluxes increase by a factor of 2 when the temperature increases from 22 to 32°C, for all particle submicron sizes. This effect, rarely observed in previous studies, could be specific to oligotrophic waters and/or to this temperature range. In all mesocosms (enriched and control mesocosms), we detected an enrichment of calcium (+500%) and a deficit in chloride (−36%) in the submicron PMA mass compared to the literature inorganic composition of the seawater. There are indications that the chloride deficit and calcium enrichment are linked to biological processes, as they are found to be stronger in the enriched mesocosms. This implies a non-linear transfer function between the seawater composition and PMA composition, with complex processes taking place at the interface during the bubble bursting. We found that the artificial phytoplankton bloom did not affect the CCN activation diameter (Dp, 50, average = 59.85±3.52nm and Dp,50,average = 93.42±5.14nm for supersaturations of 0.30 and 0.15% respectively) or the organic fraction of the submicron PMA (average organic to total mass = 0.31±0.07) compared to the control mesocosm. Contrary to previous observations in natural bloom mesocosm experiments, the correlation between the particle organic fraction and the seawater Chl a was poor, indicating that Chl a is likely not a straightforward proxy for predicting, on a daily scale, PMA organic fraction in models for all types of sea and ocean waters. Instead, the organic fraction of the Aitken mode particles were more significantly linked to heterotrophic flagellates, viruses and dissolved organic carbon (DOC). We stress that different conclusions may be obtained in natural (non-enriched) or non-oligotrophic systems.

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In the present paper, we quantify sea-to-air emission fluxes of aerosol to the atmosphere and characterize their physical and chemical properties as a function of the seawater biochemical and physical properties. Fluxes are evaluated with an original approach, a "lab in the field" experiment that preserves the seawater and atmospheric complexity while isolating air-to-sea exchanges from their surroundings. We show different features of the aerosol emission fluxes compared to previous findings.
In the present paper, we quantify sea-to-air emission fluxes of aerosol to the atmosphere and...