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

Abstract

A paradigm in paleoclimatology holds that shifts in the mean position of the Intertropical Convergence Zone were the dominant climatic mechanism controlling rainfall in the tropics during the last glacial period. We present a new paleo-rainfall reconstruction based on speleothem stable oxygen isotopes record from Colombia, which spans most of the last glacial cycle. The strength and positioning of the Intertropical Convergence Zone over northern South America were more strongly affected by summer insolation at high northern latitudes than by local insolation during the last glacial cycle, resulting in an antiphased relationship with climate in the Cariaco Basin. Our data also provide new insight into how orbital forcing amplified/dampened Intertropical Convergence Zone precipitation during millennial-scale events. During Greenland Stadial events, the Intertropical Convergence Zone was positioned close to the latitude of El Peñon, as expressed by more negative δ¹⁸O values. Greenland Interstadial events are marked by relatively high stable oxygen isotope values and reduced rainfall in the El Peñon record, suggesting a northward withdrawal of the Intertropical Convergence Zone. During some Heinrich Stadial events, and especially Heinrich Stadial 1, the Intertropical Convergence Zone must have been displaced away from its modern location near El Peñon, as conditions were very dry at both El Peñon and Cariaco.

The strength and positioning of the Intertropical Convergence Zone over northern South America were strongly related to Northern Hemisphere summer insolation during the last glacial cycle, according to speleothem oxygen isotope records from the Caracos Cave, central Colombia.