On the suitability of North Brazil Current transport estimates for monitoring basin-scale AMOC changes

Abstract

The North Brazil Current (NBC) constitutes a bottleneck for the mean northward return flow of the Atlantic Meridional Overturning Circulation (AMOC) in the tropical South Atlantic. Previous studies suggested a link between interannual to multidecadal NBC and AMOC transport variability and proposed to use NBC observations as an index for the AMOC. Here we use a set of hindcast, sensitivity, and perturbation experiments performed within a hierarchy of ocean general circulation models to show that decadal to multidecadal buoyancy-forced changes in the basin-scale AMOC transport indeed manifest themselves in the NBC. The relation is, however, masked by a strong interannual to decadal wind-driven gyre variability of the NBC. While questioning the NBC transport as a "direct" index for the AMOC, the results support its potential merit for an AMOC monitoring system, provided that the wind-driven circulation variability is properly accounted for. Key Points Set of ocean model hindcasts yields a robust interannual to decadal variability of the NBC AMOC trends are manifested in the NBC but superimposed by wind-driven gyre changes An NBC transport array can be a useful component of an AMOC monitoring system