Seasonal dynamics and annual budget of dissolved inorganic carbon in the northwestern Mediterranean deep-convection region

Ulses, Caroline; Estournel, Claude; Marsaleix, Patrick; Soetaert, Karline; Fourrier, Marine; Coppola, Laurent; Lefèvre, Dominique; Touratier, Franck; Goyet, Catherine; Guglielmi, Véronique; Kessouri, Fayçal; Testor, Pierre; Durrieu de Madron, Xavier

Deep convection plays a key role in the circulation, thermodynamics, and biogeochemical cycles in the Mediterranean Sea, which is considered to be a hotspot of biodiversity and climate change. In the framework of the DEWEX (Dense Water Experiment) project, the seasonal and annual budgets of dissolved inorganic carbon in the deep-convection area of the northwestern Mediterranean Sea are investigated over the period September 2012–September 2013 using a 3D coupled physical–biogeochemical–chemical modeling approach. At the annual scale, we estimate that the northwestern Mediterranean Sea's deep-convection region was a moderate sink of 0.5 mol C minline-formula−2 yrinline-formula−1 of COinline-formula2 for the atmosphere. The model results show the reduction of oceanic COinline-formula2 uptake during deep convection and its increase during the abrupt spring phytoplankton bloom following the deep-convection events. We highlight the major roles in the annual dissolved inorganic carbon budget of both the biogeochemical and physical fluxes, which amount to inline-formula−3.7 and 3.3 mol C minline-formula−2 yrinline-formula−1, respectively, and are 1 order of magnitude higher than the air–sea COinline-formula2 flux. The upper layer (from the surface to 150 m depth) of the northwestern deep-convection region gained dissolved inorganic carbon through vertical physical transport and, to a lesser extent, oceanic COinline-formula2 uptake, and it lost dissolved inorganic carbon through lateral transport and biogeochemical fluxes. The region, covering 2.5 % of the Mediterranean, acted as a source of dissolved inorganic carbon for the surface and intermediate water masses of the Balearic Sea and southwestern Mediterranean Sea and could represent up to 22 % and 11 %, respectively, of the COinline-formula2 exchanges with the Atlantic Ocean at the Strait of Gibraltar.

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Ulses, Caroline / Estournel, Claude / Marsaleix, Patrick / et al: Seasonal dynamics and annual budget of dissolved inorganic carbon in the northwestern Mediterranean deep-convection region. 2023. Copernicus Publications.

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