On the Role of Mesoscale Eddies in the Long-Range Export of Carbon and Nutrients from the Canary Upwelling System into the Open North Atlantic
Elisa Lovecchio, ETH Zurich, Swiss Federal Institute of Technology, Department of Environmental Systems Science (D-USYS), Zurich, Switzerland, Matthias Munnich, ETH Zentrum, Zurich, Switzerland, David Byrne, Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, Switzerland and Nicolas Gruber, ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland
Abstract:
Coastal oceans, especially the Eastern Boundary Upwelling Systems (EBUS), are regions characterized by very high productivity and by an intense lateral exchange of mass and tracers with the adjacent open oceans. However, their net contribution to the global biogeochemical cycles is still unclear. This modeling study aims to quantify and characterize the exchange between the Canary EBUS and the North Atlantic Ocean through the use of the Regional Oceanic Modeling System (ROMS) run together with a biogeochemical ecosystem module on a telescopic grid. This innovative grid combines a high resolution at the African Coast with a full Atlantic Basin perspective, allowing us to study the cross-shore exchange up to a few thousand kilometers offshore while maintaining an accurate representation of the coastal mesoscale dynamics. Our results show that the off-shore transport of coastally produced organic carbon is detectable up to 2000 km offshore and reaches up to 30% of the local net community production, substantially impacting the organic carbon balance of the open Atlantic and possibly driving the oxygen demand at depth. These lateral carbon fluxes are influenced by strong sub-regional differences in productivity, export efficiency and seasonality. In particular, the most productive sub-region is the least efficient in the lateral and vertical-advective export of organic carbon, primarily due to the nature of the physical drivers such as the low mesoscale activity. To better understand the contribution of the mesoscale activity to the transport from the shelf to the open ocean we present the mean biogeochemical composition of the water entrained in the eddy cores and the evolution of the tracers concentration during the eddy lifetime. Fundamental differences between cyclonic and anticyclonic eddies are highlighted and discussed. Finally, we assess how the intense biological activity that takes place in the eddy cores influences the net offshore transport and cycling of tracers.
