Insights into the mechanisms behind Late Holocene climate variability in the northern tropics of South America based on modern climatic analyses

At the onset of the Meghalayan Age, 4200 years ago, Earth's global climate underwent significant changes as the Southern Hemisphere received more insolation. This led to changes in global atmospheric and oceanic circulation patterns resulting in reductions in precipitation and drought in some regions of the globe while creating wetter conditions in others. Although the start of the Meghalayan in tropical latitudes remain little discussed, two recent paleoenvironmental reconstructions from high-altitude sites in the Colombian Andes provide new insights on climate variability from the beginning of the Meghalayan until about 1300 years Before Present (yr BP). These records, along with comparisons to other Colombian paleo-archives, reveal a climatic divergence: between 4150 and 2500 yr BP, the Eastern Cordillera turned wet, and between 3700 and 1300 yr BP the Western Cordillera became dry. This contrasting pattern is opposite to modern conditions where the Eastern Cordillera is overall drier than the Western Cordillera. We explore potential drivers of this divergence focusing on the period between 4200 and 1300 yr BP, using modern precipitation data from rain gauges close to the paleo-sites, and regional rainfall estimates from the Climate Hazards Group InfraRed Precipitation (CHIRPS) dataset. Our approach included wavelet analyses, identification of moisture sources, and correlation analyses involving sea surface temperatures and various climatic indices. The results suggest that a simultaneous warming of the Tropical Pacific (TP) and the Tropical North Atlantic (TNA) would explain the increase in precipitation in the Eastern Cordillera and decrease in precipitation in the Western Cordillera, likely by an increase in the frequency and/or intensity of El Niño Southern Oscillation and/or Interdecadal Pacific Oscillation-like events. • This study presents compelling evidence of anti-phase climate conditions in tropical South America (Colombia) between approximately 4.2 and 1.3 kyr BP • We propose that a concurrent warming of the tropical Pacific and Atlantic Oceans could have driven the precipitation anomaly and anti-phase climates during part of the Late Holocene • This climate scenario offers a novel framework for interpreting increased precipitation variability observed in other paleoclimate records from South America during this period, including those associated with heightened ENSO activity, the Caribbean, Cariaco Basin and others. • Given that current global warming is altering SST patterns in the tropical oceans and modifying the interhemispheric temperature gradient, future changes in the position and intensity of the ITCZ, as well as in regional precipitation patterns, are likely. • Understanding how Andean climates systems have interacted in the past provides critical context for anticipating their behavior under ongoing and future climate change.