| Volumes and Issues Contents of Issue 9 |
www.biogeosciences.net/7/2765/2010/
doi:10.5194/bg-7-2765-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
Large clean mesocosms and simulated dust deposition: a new methodology to investigate responses of marine oligotrophic ecosystems to atmospheric inputs
1Laboratoire d'Océanographie de Villefranche/Mer, CNRS-INSU, UMR7093, Observatoire Océanologique, 06230, Villefranche-sur-Mer, France
2Université Pierre et Marie Curie-Paris 6, UMR 7093, LOV, Observatoire Océanologique, 06230, Villefranche-sur-Mer, France
3Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-Sur-Yvette, France
4Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), Université Paris VII, Créteil, France
5Observatoire Océanologique de Villefranche/Mer, CNRS-UPMC, Villefranche-sur-Mer, France
6Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN), CNRS-Université Paris VI, Campus Jussieu, Paris, France
7CNRS, UMR 7621, LOMIC, Observatoire Océanologique, 66651, Banyuls/mer, France
8Université Pierre et Marie Curie-Paris 6, UMR 7621, LOMIC, Observatoire Océanologique, 66651, Banyuls/mer, France
9Laboratory of Ecology and Evolution of Plankton, Stazione Zoologica Anton Dohrn, Napoli, Italy
10Institut des Régions Arides (IRA), Medenine, Tunisia
11Parc Naturel Régional Corse, Galéria, France
*now at: Université de la Méditerranée, Centre Océanologique, Marseille, France
Abstract. Intense Saharan dust deposition occurs over large oligotrophic areas in the Mediterranean Sea and in the Tropical Atlantic, and its impact on the biogeochemical functioning of such oligotrophic ecosystems needs to be understood. However, due to the logistical difficulties of investigating in situ natural dust events, and due to the inherent limitations of microcosm laboratory experiments, new experimental approaches need to be developed. In this paper, we present a new experimental setup based on large, clean mesocoms deployed in the frame of the DUNE (a DUst experiment in a low-Nutrient, low-chlorophyll Ecosystem) project. We demonstrate that these tools are highly relevant and provide a powerful new strategy to in situ studies of the response of an oligotrophic ecosystem to chemical forcing by atmospheric deposition of African dust. First, we describe how to cope with the large amount of dust aerosol needed to conduct the seeding experiments by producing an analogue from soil collected in a source area and by performing subsequent appropriate physico-chemical treatments in the laboratory, including an eventual processing by simulated cloud water. The comparison of the physico-chemical characteristics of produced dust analogues with the literature confirms that our experimental simulations are representative of dust, aging during atmospheric transport, and subsequent deposition to the Mediterranean. Second, we demonstrate the feasibility in coastal areas to installing, in situ, a series of large (6 × 52 m3) mesocosms without perturbing the local ecosystem. The setup, containing no metallic parts and with the least possible induced perturbation during the sampling sequence, provides an approach for working with the required conditions for biogeochemical studies in oligotrophic environments, where nutrient and micronutrients are at nano- or subnano-molar levels. Two, distinct "seeding experiments" were conducted by deploying three mesocosms serving as controls (CONTROLS-Meso = no addition) and three mesocosms seeded with the same amount of Saharan dust (DUST-Meso = 10 g m−2 of sprayed dust). A large panel of biogeochemical parameters was measured at 0.1 m, at 5 m and 10 m in all of the mesocosms and at a selected site outside the mesocosms before seeding and at regular intervals afterward. Statistical analyses of the results show that data from three mesocosms that received the same treatment are highly reproducible (variability < 30%) and that there is no significant difference between data obtained from CONTROLS-Meso and data obtained outside the mesocosms.
This paper demonstrates that the methodology developed in the DUNE project is suitable to quantifying and parameterizing the impact of atmospheric chemical forcing in a low-nutrient, low-chlorophyll (LNLC) ecosystem. Such large mesocosms can be considered as 1-D ecosystems so that the parameterization obtained from these experiments can be integrated into ecosystem models.
Final Revised Paper (PDF, 3458 KB) Supplement (17 KB) Discussion Paper (BGD)
Citation: Guieu, C., Dulac, F., Desboeufs, K., Wagener, T., Pulido-Villena, E., Grisoni, J.-M., Louis, F., Ridame, C., Blain, S., Brunet, C., Bon Nguyen, E., Tran, S., Labiadh, M., and Dominici, J.-M.: Large clean mesocosms and simulated dust deposition: a new methodology to investigate responses of marine oligotrophic ecosystems to atmospheric inputs, Biogeosciences, 7, 2765-2784, doi:10.5194/bg-7-2765-2010, 2010. Bibtex EndNote Reference Manager XML
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