Sensitivity of the Atlantic Meridional Overturning Circulation to South Atlantic freshwater anomalies.
by A.A. Cimatoribus (KNMI), M. den Toom (IMAU, Utrecht University, Utrecht), S.S. Drijfhout (KNMI), H.A. Dijkstra (IMAU, Utrecht University, Utrecht),
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.
Bifurcation (a) and regime (b) diagrams for the maximum of the Atlantic meridional overturning streamfunction as a function of two control parameters: a net evaporation reduction over the Atlantic Ocean (gamma) and a dipole anomaly over the south Atlantic, summing up to zero (delta). The value of gamma for which the circulation collapses strongly depends on delta.
Cimatoribus, A.A., M. den Toom, S.S. Drijfhout and H.A. Dijkstra, Sensitivity of the Atlantic Meridional Overturning Circulation to South Atlantic freshwater anomalies.