The Impacts of Air-Sea Fluxes and Model Resolution on Seasonal and Inter-Annual Variability of the Atlantic Meridional Overturning Circulation across the OSNAP West Section

Abstract

The present study investigates the Atlantic Meridional Overturning Circulation (AMOC) in the sub-polar North Atlantic. Despite the identification of a weaker AMOC across the OSNAP (Overturning in the Subpolar North Atlantic Program) West section, low-resolution models have continuously overestimated the subpolar AMOC link to the Labrador Sea Water mass formation, underscoring the need for a deeper understanding of this process. Nevertheless, strong air-sea gas exchange from the surface to the deep ocean, associated with the ventilation of the subpolar North Atlantic by Labrador Sea Water means the Labrador Sea remains a crucial region to study. To explore the AMOC across OSNAP, we use three configurations of the NEMO (Nucleus for European Modelling of the Ocean) ocean model with varying horizontal and vertical resolutions, including a 1/60th degree Adaptive Grid Refinement In Fortran (AGRIF) nest over the Labrador Sea. The high-resolution configuration best represents the OSNAP estimates of mean AMOC. The modeled mean and seasonal AMOC using the high-resolution configuration are improved by switching to an atmospheric forcing with stronger air-sea heat loss, while showing minimal sensitivity to the Greenland melt freshwater input. The results highlight the impact of the model resolution and representation of atmospheric forcing on the seasonal and interannual variability of subpolar AMOC link to the water mass formation in the Labrador basin.