A mesocosm experiment coupled with optical measurements to assess the fate and sinking of atmospheric particles in clear oligotrophic waters
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Bressac M, Guieu C, Doxaran D, Bourrin F, Obolensky G, Grisoni JM
Geochemical Marine Letters
mesocosm, oligotrophic, saharn dust, 52 m3, Corsica, Italy, mediterranean
It has recently been postulated that lithogenic particlessuch as Saharan dust strongly influence particulateorganic carbon export to the deep ocean by acting as mineralballast. However, our understanding of the processes involvedremains scant. In the present study, optical measurementswere performed to monitor variations in the concentration,composition and size distribution of particles in suspensionwithin the water column after simulating a Saharan dust eventin very clear Mediterranean waters off Corsica in June 2010.A new methodology set up in large mesocosms proved verysuccessful in this regard. Values obtained simultaneously fromthree instruments (WetLabs ECO-BB3, WetLabs ac-9, SequoiaScientific LISST-100) provided evidence that (1) partof the Saharan dust pool has a rapid settling velocity (?24–86 m day?1), (2) particulate export following a dust event is anonlinear multi-step process and (3) export is controlled inpart by the formation of organic-mineral aggregates. Thisexperimental study provides the first insight of the complexexport processes occurring after a dust event involving bothphysical and biogeochemical forcings in clear oligotrophicwaters.
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