A mesocosm experiment coupled with optical measurements to assess the fate and sinking of atmospheric particles in clear oligotrophic waters |
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| Authors: | Matthieu Bressac Cécile Guieu David Doxaran Fran?ois Bourrin Grigor Obolensky Jean-Michel Grisoni |
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| Institution: | (1) ACRI-ST, BP 234, 06904 Sophia-Antipolis, France;(2) CNRS-INSU, Universit? Pierre et Marie Curie-Paris 6, UMR 7093, Laboratoire d’Oc?anographie de Villefranche/Mer, Observatoire Oc?anologique, 06230 Villefranche-sur-Mer, France;(3) Universit? de Perpignan, CEFREM, CNRS-UPVD, UMR 5110, 52 avenue Paul Alduy, 66860 Perpignan, France;(4) Observatoire Oc?anologique de Villefranche/Mer, CNRS, Universit? Pierre et Marie Curie-Paris 6, 06230 Villefranche-sur-Mer, France |
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| Abstract: | It has recently been postulated that lithogenic particles such as Saharan dust strongly influence particulate organic carbon
export to the deep ocean by acting as mineral ballast. However, our understanding of the processes involved remains scant.
In the present study, optical measurements were performed to monitor variations in the concentration, composition and size
distribution of particles in suspension within the water column after simulating a Saharan dust event in very clear Mediterranean
waters off Corsica in June 2010. A new methodology set up in large mesocosms proved very successful in this regard. Values
obtained simultaneously from three instruments (WetLabs ECO-BB3, WetLabs ac-9, Sequoia Scientific LISST-100) provided evidence
that (1) part of the Saharan dust pool has a rapid settling velocity (∼24–86 m day−1), (2) particulate export following a dust event is a nonlinear multi-step process and (3) export is controlled in part by
the formation of organic-mineral aggregates. This experimental study provides the first insight of the complex export processes
occurring after a dust event involving both physical and biogeochemical forcings in clear oligotrophic waters. |
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