TRACING THE NORTHERN EDGE OF SOUTHERN WESTERLIES DYNAMICS AS AN INDICATOR OF PRECIPITATION SEASONALITY IN SUBTROPICAL CHILE SINCE THE LATE PLEISTOCENE

MALDONADO, A.; DE PORRAS, M.E.

Quito

Congreso; XII Congreso Latinoamericano de Botánica; 2018

The high Andes from Subtropical Chile is a key area to study the interaction between Subtropical Southeast Pacific High and the northern edge of the Southern Westerlies Wind Belt (SW) in the past since its location, the availability of proper palaeoclimatic archives and the low human disturbance. Here, the interplay between both systems determines the current mediteranean-type climate characterized by rainy winters and dry summers and allows to trace the winter activity of SW at millennial-to-interannual time scales. The present paper aims to show the dynamics of the northern edge of the SW during the last 15ka based on pollen records from high Andean lakes (30°-33°S). First, the modern pollen-vegetation relationships were established along three different altitudinal (and climatic) west-east transects at 30°, 32°, 33°S in order to interpret the fossil pollen records in vegetation terms. Then, those past vegetation changes were interpreted as climatic changes at different spatial and temporal scales, particularly related to precipitation. High Andean lake pollen records suggest cooler/wetter than present conditions during the Late Pleistocene followed by warm/humid conditions during early Holocene which were replaced by extremely dry conditions between 7-6ka when they gradually turned to more humid conditions at 2ka. These climatic trends show a high concordance with records of lowlands from Subtropical Chile, suggesting a regional climatic control related to the SW past dynamics. Then, the comparison of these winter precipitation inferences to those of pollen records from southern Chile, sensitive to summer precipitation, allowed to establish the seasonality dynamic of the SW at centennial-to-millennial timescales. Anti-phased (or in-phase) rainfall patterns between both areas since the Late Pleistocene could be therefore explained by strong (or weak) seasonality changes of the SW. Acknowledgements: FONDECYT#1140837; #1180413.