High altitude vegetation and climate change of the Subtropical Andes of Chile (32ºS) during the last 15ka

MALDONADO A. ; CARDENAS ; MOREIRAS S.M.

Congreso; INQUA; 2015

According to future IPCC climate predictions, the Subtropical Andes of Chile (30-34°S) is one of those areas in the world which are experimenting a strong aridification trend as a consequence of the ongoing climatic change, so understanding its natural climatic variability emerge as crucial to picture future scenarios. Despite that water resources of this densely populated area originate from high Andean basins, most paleoclimatical studies from this region of Chile have been developed in the lowlands. In this work we present the pollen records from two high Andean lakes (Laguna Chica and Grande; 31º40?S, 70º30?W; 3600 masl) encompassing the last ~15ka, in order to reconstruct the climatic and vegetation dynamics in the high subtropical Chile. The cores of both lakes consist of finely laminated sediments and in Laguna Grande record, organic sedimentation overlies grey glacial clays suggesting the presence of a pro-glacial lake before 15.3 ka. The pollen assemblages show the dominance of herbs associated to the high Andean vegetation belt during the late-Pleistocene and early-Holocene. During the mid Holocene, low Andean pollen types such as Fabaceae (Adesmia-type, 40%) dominated the environments associated with Calandrinia (20-10%), Spergularia (2-15%) and Brassicaceae (2-10%). Around 2100 years BP, a steep increase of Poaceae (45-80%) associated to a concomitant decrease of Fabaceae (0-23 %) point out the replacement of low by high Andean vegetation. Fluctuating values of Fabaceae (Adesmia-type), Calandrinia, Azorella and Senecio-type pinpoint variable environmental conditions from 2100 years BP to the present. The main changes in vegetation of low to high Andean vegetation suggest effectives moisture changes which is regionally recorded and therefore suggest a strong climatic variability synchrony between low and highland in Mediterranean Chile, associated to dynamic of northern edge of Southern Westerlies Wind Belt.