Summer insolation controlled movements of Intertropical Convergence Zone during last glacial cycle in northern South America

Meridional movements of the ITCZ have produced abrupt changes in South American climate on millennial time-scales, driven by changes in cross-equatorial Atlantic sea surface temperature (SST) gradients that lasted a few thousand years. These variations in the tropical hydrological cycle have been linked to strengthening/weakening of the Atlantic Meridional Overturning Circulation (AMOC). A weak (strong) cross-equatorial Atlantic SST gradient coupled with a sluggish (enhanced) AMOC has been associated with a southward (northward) shift of the ITCZ and enhanced (reduced) ITCZ-related rainfall over northeastern Brazil (northern South America), such as during Heinrich Stadials (HS). However, the paleoclimate records typically used for this interpretation are not directly affected by the ITCZ, as they are located far to the south, a region that is mainly influenced by the South American Monsoon System (SAMS). Since records located in the SAMS domain only provide indirect evidence of past ITCZ movements, precisely dated records that cover the last glacial period from regions directly affected by the ITCZ are required to resolve the large uncertainties regarding past precipitation changes in the tropical Atlantic - South America sector of the ITCZ. We present a paleoclimate record based on δ18O values in speleothems from Colombia, located under the direct influence of the ITCZ, which documents the amplitude of the meridional displacement of the ITCZ during Greenland Stadials, Interstadials, and Heinrich events. Furthermore, we document how Northern Hemisphere summer insolation contributes to amplifying and dampening these millennial-scale events. Caracos Cave is in the El Peñon municipality in the eastern Colombian Cordillera at about ~2500 meters above sea level. The latitude of the study site coincides with the annual mean modern position of the ITCZ in northern South America. The δ18O in precipitation over the eastern Andes of Colombia is mainly controlled by the combined effects of rainfall intensity upstream and local rainfall amount associated with ITCZ activity. The latitude of the study site coincides with the annual mean modern position of the ITCZ in northern South America19,20 (Fig. 1), located to the south of the seminal paleoclimate record from the Cariaco Basin in Venezuela (~10°N) that is commonly referred to when discussing past ITCZ meridional shifts in the Atlantic-South America sector. Our results support the idea that strong teleconnections existed between the ITCZ in the Atlantic-South America sector and the high-latitude North Atlantic during the last glacial period. This positive wind-evaporation- sea surface temperature (WES) feedbacks further amplified the anomalous cross-equatorial meridional SST gradient and enhanced the southward displacement of the ITCZ. Finally, the similarities and differences between equatorial and subtropical isotope records in South America suggest that a southern ITCZ can enhance the SASM when superimposed on tropical insolation forcing. This is most evident during high-amplitude precessional cycles over subtropical South America. Reference: - Berger A and Loutre, MF. Insolation values for the climate of the last 10 million years. Quat. Sci. Rev., 10, 297-317 (1991). - Cheng, H et al. The half-lives of uranium-34 and thorium-230. Chem. Geol., 169, 17-33 (2000). - Ramirez, VM et al.Summer insolation controlled movements of Intertropical Convergence Zone during last glacial cycle in northern South America. Comm. Earth and Env. 4, 495 (2023)