Carbon export fluxes along the GEOVIDE transect in the North Atlantic (GEOTRACES GA01).

The international GEOVIDE expedition (GEOTRACES GA01, May-June 2014, spring period) had notably investigated the link between trace element cycling and the production, export and remineralization of particulate organic matter in the North Atlantic Ocean. Sampling was undertaken within different biogeochemical provinces including the Iberian Margin, 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 are known to present an important spring phytoplankton bloom leading to the export of particles. Here, we report Particulate Organic Carbon (POC) export fluxes estimated using the ²³⁴Th-based approach at 12 stations as part of the GEOVIDE expedition. POC export fluxes were deduced by combining export fluxes of ²³⁴Th_total with the POC/²³⁴Th ratio of sinking particles at the depth of export. Profiles of POC to ²³⁴Th ratio of particles were obtained for two size classes (>53µm and 1-53 µm) using in-situ pumps. Considering the large (>53 µm) particle fraction as representative of sinking material, POC export fluxes revealed latitudinal variations between provinces ranging from 25 mgC.m^-2.d^-1 in oligotrophic waters of the Iberian Plain to 62 mgC.m^-2.d^-1 in the Labrador Sea. Comparison between export and production, defined as ThE ratio, will be addressed in order to study POC export efficiencies. Preliminary data for ThE ratio show a range from 1% (Irminger Sea) to 12% (Labrador Sea) and suggest a relatively low-efficiency biological carbon pump in the North-Atlantic during late spring conditions.