AMOC Strength, Salt-Advection Feedback, and Gyre Dynamics in Models and Reanalyses

The Atlantic Meridional Overturning Circulation (AMOC) exerts a major influence on the global climate, yet its multi-scale variability and changes remain uncertain. Using four ocean reanalyses (GODAS, ORAS5, SODA, and GLORYS12) and forced ocean-sea ice (FOSI) simulations (E3SM-MPAS, CESM-POP, and CMCC-NEMO) at both coarse and mesoscale-permitting resolutions, we examine the relationships between AMOC strength, freshwater transport, salt–advection feedback, and sea surface height (SSH) as a proxy for subtropical gyre circulation. Eddy-permitting and eddy-resolving models and reanalysis generally simulate a stronger overturning, more realistic freshwater transport, and enhanced gyre circulation than coarse-resolution configurations. The salt–advection feedback is consistently negative across datasets, with statistically robust sensitivities in the North Atlantic and clear resolution dependence. In contrast, it is weak, noisy, and inconsistent across datasets in the South Atlantic, where wind-driven transport and eddy compensation can obscure the signal. SSH-derived gyre strength is linearly coupled with the AMOC strength in both the North and South Atlantic across both models and reanalyses with the exception of ORAS5 in the South. These results emphasize the close relationship between the strength of the gyre circulations and AMOC in ocean models, underscoring the importance of properly representing a quantity easily accessible through satellite observations such as SSH to better constrain the representation of the AMOC.