A Lagrangian study of the contribution of the Canary coastal upwelling to the open North Atlantic nitrogen budget

The nutrient-rich waters that upwell along the Canary Current System (CanCS) fuel elevated productivity in the nearshore and are further exported offshore into the adjacent oligotrophic North Atlantic subtropical gyre. Yet, the question of the offshore reach of this input of nutrients and its importance for the open North Atlantic biogeochemistry is still unresolved. Here, we quantify the lateral transport of both organic and inorganic nitrogen from the Canary upwelling and investigate the timescales, reach and structure of offshore transport of upwelled particles using a Lagrangian approach. To this end, we track all water particles entering the coastal ocean and upwelling along the Northwest African coast between 14N and 35N, as simulated by an eddy-resolving configuration of the ROMS model. We find a strong diversity of the CanCS in terms of the reach and efficiency of the offshore transport of water and nitrogen. Around 1/3 of the total offshore transport of water occurs around major capes along the CanCS that are favorable to the formation of persistent filaments. These are associated with an enhanced offshore transport of water and nitrogen by up to a factor 4 in the first 400km. Our analysis shows that water recirculation, likely associated with mesoscale eddies, dominates offshore transport up to 500km for particles upwelling north of Cape Blanc, but plays a smaller role in the transport of particles upwelling along the Mauritanian coast. Finally, we found the Canary upwelling nitrogen supply to the North Atlantic Tropical Gyral (NATR) and the North Atlantic Subtropical Gyral East (NASE) Longhurst provinces to amount to around 45±15\% and 3.5±1.5\% of the total new production in the two provinces, respectively. Our results highlight the importance of the CanCS upwelling as a key source of nutrient to the open North Atlantic and stress the need for improving the representation of Eastern Boundary Upwelling Systems in general in the global coarse resolution models.