Sensitivity of the Atlantic Meridional Overturning Circulation to South Atlantic freshwater anomalies

TL;DR

This study investigates how freshwater anomalies in the South Atlantic influence the stability and potential collapse of the Atlantic Meridional Overturning Circulation (AMOC), highlighting the importance of basin-scale salinity contrasts.

Contribution

It demonstrates that South Atlantic freshwater anomalies can significantly alter AMOC stability, emphasizing the role of regional salinity patterns in climate models.

Findings

Dipole anomalies can collapse the AMOC without additional forcing.

Biases in freshwater fluxes affect AMOC response to perturbations.

South Atlantic processes are crucial for AMOC stability.

Abstract

The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to changes in basin integrated net evaporation is highly dependent on the zonal salinity contrast at the southern border of the Atlantic. Biases in the freshwater budget strongly affect the stability of the AMOC in numerical models. The impact of these biases is investigated, by adding local anomaly patterns in the South Atlantic to the freshwater fluxes at the surface. These anomalies impact the freshwater and salt transport by the different components of the ocean circulation, in particular the basin--scale salt--advection feedback, completely changing the response of the AMOC to arbitrary perturbations. It is found that an appropriate dipole anomaly pattern at the southern border of the Atlantic Ocean can collapse the AMOC entirely even without a further hosing. The results suggest a new view on the stability of the AMOC, controlled by processes in the South Atlantic.