Middle to Late Holocene environmental dynamics of the subtropical Andes (32°-36°S)

DE PORRAS, M.E.; CAVAGNA, E.I.; MARTEL-CEA J.A.; MALDONADO, A.

Roma

Congreso; XXI Congress of the International Union for Quaternary Research (INQUA); 2023

The subtropical Andes (32°-36°S) are one of those areas in the world that has been experimenting a strong trend to more arid conditions as the result of increased temperatures and a reduction in (winter) precipitation due to the ongoing climate change. Precipitation in the high Andes, related to the Southern Westerlies, is the source of water for central Chile and Argentina becoming therefore a key resource in socio-environmental terms. The scarce long-term records in the Andes located in the western lowlands point out that this region experimented widespread and extreme arid conditions during the Middle Holocene. Hence, studying the high Andean environments response to such conditions in the past would provide some clues to face the future scenarios in this region. Thus, this work aims to reconstruct the paleoenvironmental dynamics of the subtropical Andes (32°-36°S) at centennial/sub-centennial scale by presenting the pollen record of Laguna Corazón (LCO; 35,14°S-70,21°W) and other high Andean records spanning the Middle to Late Holocene. Naked-eye description, RX radiographs, Loss on Ignition, and pollen analysis were performed on the 2.4-meter long sediment core of LCO dating back 5400 yrs BP. The sedimentary record is mostly composed of dark-brown laminated silts and presents a volcanic ash layer at 21-24cm depth that according to the chronological control could be attributed to the 1932 Quizapu eruption. The LCO record reflects the development of a grass steppe with a millennial scale drier-than-present phase between 5400-3000 yrs BP, more humid conditions than present between 2700-1100 cal yrs BP followed by a decrease in moisture up to 300 cal yrs BP when similar than present conditions established but under a high environmental variability. Other high Andean lake records at 32°, 33° and 36°S point out drier-than-present conditions during the Middle Holocene even the peak/amelioration of such conditions is asynchronous probably related to their latitudinal/longitudinal position regarding the precipitation source. FONDECYT #1180413.