Multidecadal variability of the North Brazil Current

Abstract

The Atlantic meridional overturning circulation (AMOC), which carries warm water to high northern latitudes near the surface and returns cold water in the deep ocean to the Southern Hemisphere, affects and is affected by global climate change. There has been debate as to whether the AMOC has begun slowing down due to global warming, but research on AMOC variability based on instrumental records is limited. One possible indicator of change in the AMOC is the North Brazil Current (NBC), a strong current that flows northward in the tropical South Atlantic, connecting the North and South Atlantic oceans, and plays an important role as a major pathway for surface return flow in the AMOC. Zhang et al. calculated how NBC varies on multidecadal time scales based on a record of 50 years of observations off the coast of Brazil. They found that NBC transport changes are correlated with Labrador Sea deep convection (important for deepwater formation) and with a broad pattern of sea surface temperature anomalies in the Atlantic (sometimes referred to as the Atlantic Multidecadal Oscillation or Atlantic Multidecadal Variability), both of which have previously been linked to AMOC fluctuations. The researchers therefore suggest that observed NBC variability is a useful indicator of AMOC variations. They confirm this using a climate model simulation. Furthermore, the authors note that although some studies have suggested that the AMOC is slowing down due to global warming, NBC shows multidecadal variability but no significant slowing trend over the past 50 years. (Journal of Geophysical Research‐Oceans, doi:10.1029/2010JC006812, 2011)