Mid-Holocene environmental dynamics of the subtropical Andes (33°S)

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

Congreso; IAL IPA 2022; 2022

The subtropical Andes (32°-35°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. The scarce long-term records in the Andes located southwards and in the western lowlands point out that this region experimented widespread and extreme arid conditions during the Middle Holocene. Hence, studying the high Andean environment response to such conditions in the past would provide some clues to face the future scenarios in this region. Thus, this paper aims to reconstruct the environmental dynamics of the subtropical Andes at centennial time scale based on the pollen record of Laguna Chepical (LCH; 3100 masl, 33°S). Naked-eye description, RX radiographs, Loss on Ignition and pollen analysis were performed on the 130cm long sediment core of LCH. The sedimentary record presents gray clays at the base (260-240cm) followed by inorganic gytjja (240-190cm) and organic gytjja (190-130cm). The LCH pollen record reflects that a periglacial environment with Sub-Andean and Low Andean vegetation occurred between 7800-7400 cal yrs BP followed by a dominance of Low Andean vegetation dominance in a post-periglacial environment with variable lake levels until 6200 cal yrs BP. A drastic decrease of pollen types of Low Andean vegetation along with a drop of azonal pollen types point out the driest period between 6200-4800 cal yrs BP followed by a gradual rise of moisture reflected by the increase (decrease) of Low (Sub-) Andean pollen types until 3200 cal yrs BP. As a result, the LCH record indicate that drier-than-present conditions occurred in the subtropical Andes (33°S) during the Middle Holocene and that zonal and azonal vegetation effectively responded to such centennial scale changes. FONDECYT #1180413; #1220203.