Quantification of the lithogenic carbon pump following a simulated dust-deposition event in large mesocosms

[摘要] Lithogenic particles, such as desert dust, have been postulated to influenceparticulate organic carbon (POC) export to the deep ocean by acting asmineral ballasts. However, an accurate understanding and quantification ofthe POC–dust association that occurs within the upper ocean is required inorder to refine the "ballast hypothesis". In the framework of the DUNE (aDUst experiment in a low-Nutrient, low-chlorophyll Ecosystem) project, twoartificial seedings were performed seven days apart within large mesocosms.A suite of optical and biogeochemical measurements were used to quantifysurface POC export following simulated dust events within a low-nutrient,low-chlorophyll ecosystem. The two successive seedings led to a 2.3–6.7-foldhigher POC flux than the POC flux observed in controlledmesocosms. A simple linear regression analysis revealed that the lithogenicfluxes explained more than 85% of the variance in POC fluxes. On thescale of a dust-deposition event, we estimated that 42–50% of POC fluxeswere strictly associated with lithogenic particles (through aggregation andmost probably sorption processes). Lithogenic ballasting also likelyimpacted the remaining POC fraction which resulted from the fertilizationeffect. The observations support the "ballast hypothesis" and provide aquantitative estimation of the surface POC export abiotically triggered bydust deposition. In this work, we demonstrate that the strength of such a"lithogenic carbon pump" depends on the biogeochemical conditions of thewater column at the time of deposition. Based on these observations, wesuggest that this lithogenic carbon pump could represent a majorcomponent of the biological pump in oceanic areas subjected to intenseatmospheric forcing.

[学科分类] 地球化学与岩石