Simplifying the Dynamics of the Atlantic Meridional Overturning Circulation at 26°N

A decline in Atlantic meridional overturning circulation (AMOC) strength has been observed between 2004 and 2008 by the RAPID array, this weakened state of the AMOC persisting until 2017. Climate model and paleo-oceanographic research suggests that the AMOC may have been declining for decades or even centuries before this, however direct observations are sparse prior to 2004, giving only ‘snapshots’ of the overturning circulation. Previous studies have used linear models based on upper layer temperature anomalies to extend earlier, but these ignore changes in the deep circulation that are beginning to emerge in the observations of AMOC decline.

We use a linear statistical model of AMOC variability based on RAPID data, and associated physically with changes in thickness of the persistent upper, intermediate and deep layers at 26°N. Boundary density anomalies at depths representing each layer are used to develop a multiple linear regression model which explains approximately 70% variance in the open ocean component. Using this regression model, we can estimate relative AMOC strength from a reduced number of observations, opening up the use of historical data that are insufficient for the usual AMOC estimation method.