Abstract

Away from the continental boundaries, the variability of the global ocean is frequently dominated by eddies. Despite this interior chaos, ocean boundary pressures on opposing sides of a basin can vary coherently on interannual to decadal timescales while exhibiting large-scale spatial structure. As part of the OceanBound project, we use an adjoint model to directly quantify the drivers of variability in Atlantic boundary pressures and the associated basin-wide geostrophic transport. The Atlantic Meridional Overturning Circulation (AMOC) is the overall effect of basin-wide meridional transport in the Atlantic and is a central component of the climate system. We use an adjoint modelling framework to investigate the forcings and relevant timescales behind the interannual variability of the basin-wide geostrophic transport in the subtropical North and South Atlantic. We find that a combination of wind-driven and heat-driven variability, operating on a maximum timescale of 10 years, can explain 79-94% of the variability exhibited by the model. Wind-driven variability is mostly interannual and essential in all cases (64-88% explained variability). The heat-driven variability is largely decadal and only noticeable in the subtropical North Atlantic (48-52% explained variability). We then identify a rogues’ gallery of four spatial patterns of sensitivity that are relevant to our reconstructions.