Tropical Atlantic variability during the Last Millennium

Climate variability in the Tropical Atlantic is complex with strong ocean-atmosphere coupling, where the sea surface temperature (SST) variability impacts the hydroclimate of the surrounding continents. One of the main modes of SST variability in this region is known as the Atlantic Niño. Its dynamics are dominated by the Bjerknes Feedback, much like the Pacific El Niño. It is characterized by the coupling between SST in the eastern Equatorial Atlantic, zonal wind anomalies, changes in the thermocline depth, and consequent upwelling anomalies. The development of SST anomalies in the Equatorial Atlantic can be explained in terms of an oscillator model of recharge and discharge of heat content. This model is represented by the Bjerknes Feedback Index, which is a set of components representing the mechanisms that enhance (i.e., Thermocline, Zonal Advective, and Ekman feedbacks) or limit (Thermal and Dynamical damping) the growth of the SST anomalies. The pre-industrial millennium is vastly studied with respect to the responses to natural forcing, given the similarity of the climate background with present-day conditions. In addition, this period is known for the occurrence of large volcanic eruptions that were able to change the ocean-atmosphere interaction. Here, we propose to investigate the interannual variability of the Tropical Atlantic during the Last Millennium (LM, 850 to 1849 CE) in terms of the Bjerknes Feedback Index. For that, we rely on results from the Last Millennium period from the Paleoclimate Modeling Intercomparison Project (PMIP4) contribution to Climate Model Intercomparison Project phase 6 (CMIP6).