Mesopelagic carbon remineralization along the GEOVIDE transect in the North Atlantic (GEOTRACES GA01).

The international GEOVIDE expedition (GEOTRACES GA01, May-June 2014, spring period) aims at providing a better understanding on key trace metal biogeochemical cycles in the North Atlantic Ocean. Sampling was undertaken at 12 stations located within different biogeochemical provinces including the Iberian Basin, the West European Basin, Reykjanes Ridge, Irminger Sea, Greenland Margin and the Labrador Sea, showing contrasted physical, biological and chemical characteristics. Some of these areas support annually recurrent spring phytoplankton bloom potentially generating a pulse of sinking particles. The carbon transfer is known to be efficient in the North Atlantic, but large uncertainties remain about the remineralization processes affecting the sinking particles in the mesopelagic layer. Carbon remineralization fluxes were traced by the excess, non-lithogenic particulate barium (Ba_xs) proxy (Dehairs et al., 1997) and revealed large variation between provinces ranging from 61 mg C.m^-2.d^-1 near the Greenland Margin to 250 mg C.m^-2.d^-1 in the Labrador Sea (100-1000m depth). This high remineralization flux was probably related to an important bloom developed before the sampling and also to the Labrador Seawater formation generating a deep remineralization layer. Generally, remineralization seems to be an important process questioning the real efficiency of the carbon transfer to the deep North Atlantic Ocean.