AOPP Seminar - Lagrangian Perspectives on the Meridional Overturning Circulation in the North Atlantic Ocean

The Atlantic Meridional Overturning Circulation (AMOC) plays a critical role in the global climate system through the redistribution of heat, freshwater and carbon. However, the distribution of the strength and variability of overturning across the individual circulation pathways of the North Atlantic Subpolar Gyre (SPG) and the Nordic Seas overflows remains poorly understood. In this talk, we will explore the nature of the North Atlantic overturning circulation by introducing a novel Lagrangian framework to analyse ocean general circulation models.

We will find that dense water formation along the longest SPG pathways sourced from the central and southern branches of the North Atlantic Current (NAC) accounts for more than half of the time-mean strength of the AMOC in the eastern subpolar North Atlantic. Meanwhile, the strong seasonality of subpolar overturning is explained by water parcels circulating rapidly in the upper Irminger and Central Iceland Basins, whose along-stream transformation depends on their month of arrival into the eastern SPG. Looking beyond seasonal timescales, we will also see that the amount of dense water formed along the path of the SPG in models can be skilfully predicted, based solely on the volume transport of light waters flowing northward in the branches of the NAC, which is closely related to the strength of the SPG circulation.

Together, these findings highlight the fundamental roles of the geometry and connectivity of circulation pathways in governing the strength and variability of the AMOC in the North Atlantic Ocean.