Impact of tides on the North Western European shelf carbon pump

It has been suggested that continental shelves disproportionally contribute to global oceanic CO2 uptake from the atmosphere, in particular through the efficient CO2 sinks of the biologically productive mid- and high latitude shelves. For the North Western European Shelf (NWES), contributions of different biological and hydrodynamic drivers of the shelf carbon pump, however, remain poorly constrained. We here use the flexible coupled hydrodynamic-biogeochemical modeling system SCHISM-ECOSMO to investigate how tidal forcing, as one of the dominant hydrodynamic features on the NWES, influences the efficiency of the continental shelf pump. Tidal impacts on biological productivity and carbon cycling are assessed by comparing hindcast simulations with and without tidal forcing. We show that tides substantially increase net primary productivity on the NWES and find a significant contribution from vertical mixing induced by internal tides. Our results further demonstrate that the enhanced productivity and inorganic carbon sequestration in the tidal scenario translates into an increased oceanic CO2 uptake, even though tidal currents reduce particulate carbon deposition in the shelf sediments. This suggests that tides play an important role for the efficiency of the continental shelf pump by promoting net carbon export from the NWES to the adjacent North Atlantic.