AMOC-forced southward migration of the ITCZ under a warm climate background

Northern northeastern Brazil (NEB) is a climate change hotspot due to its high biological and social vulnerability to ongoing and future hydroclimate changes. Precipitation in this region is influenced by the Intertropical Convergence Zone (ITCZ), which is largely controlled by the strength of the Atlantic Meridional Overturning Circulation (AMOC). Accordingly, the projected weakening of the AMOC due to anthropogenic global warming may substantially change NEB hydroclimate. Heinrich Stadials (HS), past millennial-scale events during which the AMOC was significantly weaker, provide important insights into the AMOC-ITCZ dynamics. This is especially true for those HS that occurred under similar to modern boundary conditions. HS10 (ca. 110 thousand years ago) was the first HS of Marine Isotope Stage 5, providing an ideal target for investigating AMOC-ITCZ dynamics under relatively warm climate conditions. Here we investigate the response of the surface and deep western equatorial Atlantic (WEA) circulation, as well as NEB precipitation to HS10. Therefore, we use foraminiferal carbon and oxygen stable isotopes and bulk sediment major elemental data from a marine sediment core retrieved from the WEA. Our results record a weakening of the AMOC during HS10 and show a concurrent increased WEA upper stratification and precipitation over NEB. We suggest that the mechanism controlling the WEA upper ocean stratification during HS depends on the background climate. Furthermore, we infer that the southward shift of the ITCZ during HS10 was more limited if compared to the shifts that occurred under colder climate background. Our findings provide useful insights into how a weakening of the AMOC under a relatively warm climate can impact the ITCZ and tropical South American precipitation.

Duke Scholars

Author Paul A. Baker Earth and Climate Sciences