Mid-Holocene climatic variability reconstruction from pollen records (32°-52°S, Argentina)

This study reviews 42 published pollen records to gain a better understanding of Holocene climate variability, especially of the past displacement and location of the arid-semiarid region (ASR) between 32° and 52°S in Argentina. At present, the ASR is delimited approximately between the 500 mm isohyet in the Pampa region and the 300 mm isohyet in the Andean sector (south of 37°S) represented by arid and semiarid climate types where precipitation can be as low as 200 mm. Mid-Holocene climatic variability affected the regional vegetation patterns and the borders of the ASR. Paleoenvironmental reconstruction is based on comparison of fossil pollen records from different depositional environments. Maps of distribution patterns of plant formations are reconstructed at 2000±500 year intervals from 8000 to 4000 14C years BP. Vegetation changes are mainly explained by changes in the position and the seasonal amplitude of latitudinal shifts of the Pacific and Atlantic Anticyclones and of the westerlies. From 8000 to 4000 BP the eastern limit of the ASR was displaced eastward. The western limit reached the maximum eastward displacement in the southern extreme of Patagonia at 6000 years BP. At this time, at the center of ASR, shrub steppes and the Monte developed, suggesting maximum dry conditions and the establishment of the Arid Diagonal north of 42°S, while the present-day Espinal-Dry Pampa ecotone became established. At 4000 years BP paleodata suggest a transitional stage towards the present situation of the ASR.