A possible 10-15 year variability of the AMOC and its climatic impacts

• Main Authors: Nnamchi, H., Farneti, R., Keenlyside, N., Kucharski, F., Mojib, L., Reintges, A., Martin, T.
• Format: Conference Object
• Language: English
• Published: 2023
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5018732

An important feature of ocean circulation in the Atlantic is the cross-equatorial and northward transport of water masses at the surface and southward transport at the bottom of the ocean by the Atlantic Meridional Overturning Circulation (AMOC). However, the link between the AMOC and tropical Atlantic variability remain poorly understood. This is partly due lack of long-term observations of the AMOC, with the longest direct measurements available since 2004. Here we construct a dynamic sea-level proxy of the AMOC variability during the twentieth century, which is strongly correlated with the AMOC index during the observational period from 2005-2019 (r=0.50; p=1.48×10-9). This sea-level proxy exhibits a 10-15 year periodicity similar to the pan-Atlantic Decadal Oscillation (ADO) – the north-south bands of alternate anomalies in surface-ocean temperatures with the maximum variance over the tropical Atlantic, and winds from colder bands to the warmer. The sea level-derived proxy leads the ADO pattern by several years, through the interactions of overturning and gyre circulations with Kelvin wave anomalies that propagate from the North Atlantic to the low latitudes and by the thermocline feedback in the Atlantic cold tongue region. The peak of the sea surface temperature variability in the tropical Atlantic in turn drives inter-hemispheric atmospheric teleconnections represented by negative North Atlantic Oscillation phase over the North Atlantic. These findings imply that, rather than a passive role postulated by the prevailing thermodynamic paradigm, AMOC-related ocean circulation plays an active role in ADO variability.