Warm tropical oceans and ENSO flavours behind the late Holocene change in hydroclimates in northern South America

Abstract. At about 4,000 years ago the earth’s global climate underwent significant transformations resulting from changes in solar insolation. Manifestations of this change are relatively well known in higher latitudes, however, in the American tropics these are still not fully identified or understood. Recent paleo-environmental reconstructions based on paleolimnological and vegetational histories of two Colombian Andean sites suggest that between ~4,150 and 2,500 yr BP the Eastern Cordillera (EC) witness wetter anomalies, while the Western Cordillera (WC) suffered from drier anomalies between ~3,700 and 1,750 yr BP. Results from analyses of modern precipitation series from weather stations close to the study sites indicate that the long-term mean annual cycle of precipitation in both sites is out-of-phase and that precipitation anomalies on the western (eastern) site are negatively (positively) correlated with sea surface temperatures in the tropical Pacific (Tropical Atlantic). Hence that we propose that both oceans warmed up during the late Holocene, likely from a more active ENSO and ENSO flavours. With the current global rise in atmospheric temperature and the warming of tropical oceans, this study sheds light on possible anomalous effects on precipitation over the northern Andes.