Mesoscale Contribution to the 3D Cycling of Organic Matter in the Canary Upwelling System

Mesoscale eddies and coastal filaments are abundant in productive Eastern Boundary Upwelling Systems. These structures have been shown to be able to transport significant amounts of water and tracers from the nearshore to the open waters. Here we quantify the specific contribution of mesoscale eddies and coastal filaments to the total offshore transport of organic carbon in the Canary Upwelling System (CanUS) up to 2000 km from the coast. We analyse high spatial and temporal resolution model data produced running the coupled Regional Oceanic Modeling System (ROMS) with a biogeochemical ecosystem model on a high resolution full-Atlantic telescopic grid. To disentangle the small scale flux contribution from the total, we employ a sea surface height-based eddy detection algorithm and a newly developed sea surface temperature-based filament detection algorithm. We find that, near the CanUS coast, the offshore transport of organic carbon is driven by narrow, but intense coastal filaments, which are responsible for 80% of the offshore flux at 100 km offshore. Filaments are the major source of organic material for the open waters up to 500 km offshore. Beyond 500 km from the coast, eddies (especially cyclons) drive the mesoscale offshore transport of organic carbon, contributing about 20 % to the total flux up to 2000 km into the North Atlantic gyre. Although eddies propagate slowly, they contain roughly 30 % of the organic carbon in the open sea euphotic layer, therefore representing a precious reservoir of organic carbon for the open waters. Our results confirm that small scale processes drive the coastal-open ocean coupling in the organic carbon cycle, which has important implications for both modelling and observational studies of the biological pump.