Late Holocene climate quantitative reconstruction from the chilean Andes (20°S) based on rodent midden pollen records

DE PORRAS, M.E.; ZAMORA-ALLENDES, A.; MALDONADO, A.

Medellín

Simposio; LOTRED-SA 3rd International Symposium; 2014

Past climate of Central Andes (18-24°S) has been studied because of:(1) its strong impact that would have had on the hydrologic resources of this region where water is a crucial factor for plant and animal survival as well as for human occupation and, (2) the potential links with continental and interhemispheric scale atmospheric circulation. Particularly, past climatic and environmental dynamics from arid and semiarid areas of northern Chile have been mainly reconstructed based on fossil rodent midden (pollen and plant macrofossils) records given that ?standard? depositional environments are scarce. However, past climatic scenarios have been qualitatively reconstructed up to the present in spite of the importance of quantifying the magnitudeof climatic changes and their impact on environments and resources. The present paper presents the Late Holocene changes in precipitation and temperature quantitatively reconstructed from rodent midden pollen data from the Chilean Andes (20°S) using a transfer function based on a Weighted Averaging (WA) regression. The pollen-climate calibration model consisted on selected samples from a 78 modern rodent midden dataset collected along five altitudinal and climatic west-east transects (18°, 20°, 22°, 24°, 25°S) on the western slopesof the Andes. Climate data (mean annual temperature and annual precipitation) were taken from WorldClim database and checked with the instrumental data available. The statistical performance of the pollen-precipitation Pyear; r2=0.81, RMSEP=5.57mm, 17.4% of the sampled range and MaxBias=5.92mm) and pollen-temperature 45 (Tyear; r2=0.86, RMSEP=0.71°C, 16,5% of the sampled range and MaxBias=0.77°C) model was similar to other comparable pollen-climatemodels from South America. Fossil pollen data consisted on two series of fossil rodent middens collected at 20°S (3550 and 3750 masl). Reconstructed climatic variables suggest a quite dynamic environment in the Chilean Andes during the Late Holocene. Between 2.5-0.5 ka, alternating colder (3.8-4.9°C) and wetter (93-86mm) vs. drier (73-86mm) and warmer (4.9-6.6°C) conditions characterizednorthern Chile scenarios. Two humid pulses (93mm) associated with lower temperatures (3.7°C) occurred around 2 and 1.1ka pointing out to the wettest phase during the Late Holocene. A precipitation decrease (-4.87mm) and temperature increase (+0.52°C) indicate drier conditions than present during the last 0.5ka interrupted by a humid pulse (+1.37mm) around 0.1ka that point out to the transition to the present climatic features.FONDECYT #3130511; #1130279.