Quantification of the lithogenic carbon pump following a simulated dust-deposition event in large mesocosms
- 1ACRI-ST, BP 234, 06904 Sophia-Antipolis, France
- 2CNRS-INSU, Université Pierre et Marie Curie-Paris 6, UMR7093, Laboratoire d'Océanographie de Villefranche/Mer, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France
- 3Université de Perpignan Via Domitia, CEFREM, CNRS-UPVD, UMR5110, 52 avenue Paul Alduy, 66860 Perpignan, France
- 4Université Paris Diderot, Sorbonne Paris Cité, Université Paris Est Créteil, UMR CNRS 7583, Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), 61 av. Gal de Gaulle, 94010 C France
- 5Observatoire Océanologique de Villefranche/Mer, CNRS, Université Pierre et Marie Curie-Paris 6, 06230 Villefranche-sur-Mer, France
- 6CNRS-INSU-IRD, Université Pierre et Marie Curie, UMR7159, LOCEAN: Laboratoire d'Océanographie et du Climat: Expérimentation et Approches Numériques, 4 Place Jussieu – 75252 Paris Cedex 05, France
Abstract. Lithogenic particles, such as desert dust, have been postulated to influence particulate organic carbon (POC) export to the deep ocean by acting as mineral ballasts. However, an accurate understanding and quantification of the POC–dust association that occurs within the upper ocean is required in order to refine the "ballast hypothesis". In the framework of the DUNE (a DUst experiment in a low-Nutrient, low-chlorophyll Ecosystem) project, two artificial seedings were performed seven days apart within large mesocosms. A suite of optical and biogeochemical measurements were used to quantify surface POC export following simulated dust events within a low-nutrient, low-chlorophyll ecosystem. The two successive seedings led to a 2.3–6.7-fold higher POC flux than the POC flux observed in controlled mesocosms. A simple linear regression analysis revealed that the lithogenic fluxes explained more than 85% of the variance in POC fluxes. On the scale of a dust-deposition event, we estimated that 42–50% of POC fluxes were strictly associated with lithogenic particles (through aggregation and most probably sorption processes). Lithogenic ballasting also likely impacted the remaining POC fraction which resulted from the fertilization effect. The observations support the "ballast hypothesis" and provide a quantitative estimation of the surface POC export abiotically triggered by dust deposition. In this work, we demonstrate that the strength of such a "lithogenic carbon pump" depends on the biogeochemical conditions of the water column at the time of deposition. Based on these observations, we suggest that this lithogenic carbon pump could represent a major component of the biological pump in oceanic areas subjected to intense atmospheric forcing.