INTERTROPICAL CONVERGENCE ZONE DYNAMICS AND NORTHERN SOUTH AMERICA RAINFALL VARIABILITY DURING THE LAST 50 KYRS FROM COLOMBIAN STALAGMITES

Understanding the extent of latitudinal movements of intertropical convergence zone (ITCZ) during different climatic boundaries and millennial climatic oscillations (Dansgaard-Oeschger; DO and Heinrich events; HE) is essential to improve climate model output. Although there is compelling evidence about the behavior of tropical rainfall variations in response to DO and HE events, the extent and magnitude of these changes is poorly constrained. Furthermore, the potential importance of the ocean in forcing or modulating tropical climate over these time-scales is of tremendous interest. Despite this, few continuous, long-term records exist from locations sensitive to ITCZ dynamics. In this study, we provide a stable oxygen isotope record constrained by 22 uranium-thorium absolute dates from four partially overlapping stalagmites collected in the Eastern Colombian Andes spanning the last 50 kyrs. The area is located at ~6 ° N where the mean annual climatological cycle presents a bi-modal rainfall pattern controlled by the seasonal migrations of the ITCZ. This precipitation-sensitive composite record and its regional correlation with other South American records indicates that the continental ITCZ over South America experienced orbital-scale drifts and millennial-scale oscillations (dry/wet) during the last 50 kyrs. Our results suggest a drift in the ITCZ towards the southern hemisphere from the early to the middle Holocene following changes in the boreal summer insolation, and from 50 kyrs towards the last glacial maximum accompanying changes in ice volume on the planet. On millennial time scales the Colombian record shows variable response to DO and HE events sometimes displaying coherent responses with records north and south from the equator. During the largest DO events, the Colombian record is generally dry and in phase with records south of the equator, while weaker DO events are coincident with wet conditions in Colombia and in-phase with other northern South American records. These results suggest a possible relationship between the magnitude of the temperature anomalies in the North Atlantic and the degree of displacement of the ITCZ. During Heinrich events the Colombian record is wet and coherent with records from the south indicating that latitudinal movements of the ITCZ were relatively small.