EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

AMOC variations modulated by Tropical Indio-Atlantic SST Gradient

Brady Ferster1,2, Leonard Borchert3, Juliette Mignot2, and Alexey Fedorov1,2
Brady Ferster et al.
  • 1Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA
  • 2Sorbonne Universités (SU, CNRS, IRD, MNHN), LOCEAN Laboratory, Institut Pierre Simon Laplace (IPSL), Paris, France
  • 3Center for Earth System Research and Sustainability CEN, Universität Hamburg, Germany

A potential future slowdown or acceleration of the Atlantic Meridional Overturning Circulation (AMOC) would have profound impacts on global and regional climate. Recent studies have shown that AMOC responds, among many other processes, to anthropogenic changes in tropical Indian ocean (TIO) temperature. However, internal unforced co-variations between these two basins are largely unexplored as of yet. Here, we use the ERSST v5, HadISST v1, and COBE v2 gridded observational products for the period 1870-2014, as well as dedicated simulations with coupled climate models, and show that internal changes in sea surface temperature gradients between the Indian and Atlantic Ocean (SSTgrad) can drive teleconnections that influence internal variations of North Atlantic climate and AMOC.

We separate the unforced observed component (i.e., internal signal) from the forced signal following the residuals method presented by Smith et al. (2019). In the absence of direct AMOC observation we estimate AMOC variability from an SST index (SSTAMOC; Caesar et al., 2018). We find a robust observed relationship between the unforced tropical SSTgrad and SSTAMOC when TIO leads by ~25 years. This time-lag is in line with a recently described mechanism of anomalous tropical Atlantic rainfall patterns that originate from TIO warming and cause anomalously saline tropical Atlantic surface water which slowly propagate northward into the subpolar North Atlantic, ultimately altering oceanic deep convection and AMOC (Hu and Fedorov, 2019; Ferster et al. 2021). Our study now suggests that it is the tropical SSTgrad that drives those AMOC changes, with a limited role for the western tropical Pacific. Pre-industrial control simulations with the IPSL-CM6A-LR model confirm this relationship, indicating a time lag of ~25 years between SSTgrad and SSTAMOC variations. These simulations also confirm that the SSTAMOC is representative of unforced AMOC variations when SSTAMOC leads by 5 years. This work therefore indicates that an unforced pathway between tropical ocean temperature and AMOC exists with a ~20 year lag, which opens the potential for using SSTgrad as precursor to predict future AMOC changes.


Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G., & Saba, V. (2018). Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature, 556(7700), 191-196.

Ferster, B. S., Fedorov, A. V., Mignot, J., & Guilyardi, E. (2021). Sensitivity of the Atlantic meridional overturning circulation and climate to tropical Indian Ocean warming. Climate Dynamics, 1-19.

Hu, S., & Fedorov, A. V. (2019). Indian Ocean warming can strengthen the Atlantic meridional overturning circulation. Nature climate change, 9(10), 747-751.

Smith, D. M., Eade, R., Scaife, A. A., Caron, L. P., Danabasoglu, G., DelSole, T. M., ... & Yang, X. (2019). Robust skill of decadal climate predictions. Npj Climate and Atmospheric Science, 2(1), 1-10.

How to cite: Ferster, B., Borchert, L., Mignot, J., and Fedorov, A.: AMOC variations modulated by Tropical Indio-Atlantic SST Gradient, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7011,, 2023.