Connections Between AMOC, Meridional Heat Transport, and Heat Content in the North Atlantic from Satellite Altimetry

The decade-long records of the Atlantic meridional overturning circulation (MOC) and ocean meridional heat transport, sea surface height and Florida Current transports are used to examine controlling mechanisms of heat content variations in the North Atlantic and their influence on air-sea heat fluxes.  Sea surface height is used as a proxy for ocean heat content and to extend transport time series back to 1993. 

Through calculations of lead-lag relationships, we find that northward shifts in the Gulf Stream path are associated with an increase in heat content in the region.  These meridional shifts in the Gulf Stream path are driven by changes in the North Atlantic Oscillation (NAO), with the NAO leading by 6 months.  South of the Gulf Stream in the recirculation region, heat content changes are led by changes in Florida Current transports.  Both near the Gulf Stream path and south of the Gulf Stream in the recirculation region, excess heat content anomalies generated by ocean heat transport anomalies result in heat fluxes from the ocean to the atmosphere. In addition, changes in upper ocean heat content may be linked to changes in geostrophic circulation: we also find that heat deficits in the North Atlantic Current region lead to a reduction in the Atlantic MOC strength at 41N. 

These results show a link between changes in oceanic heat transport convergence near the Gulf Stream and North Atlantic Current and heat fluxes from the ocean to the atmosphere, with changes in ocean circulation driving air-sea fluxes.  While modeling studies have focused on the role of the sinking regions in the Labrador Sea in generating Atlantic MOC variability, this observational analysis suggests that interannual variations in ocean transport variability in the subtropics, perhaps in response to NAO-related wind forcing, can have non-local impacts on both air-sea fluxes and on the Atlantic MOC further to the North.