Changes in climate, vegetation and fire regimes in SW Mendoza, Argentina over the last 6400 cal-yr-BP: the Laguna El Sosneado record

NAVARRO, D.; WHITLOCK, C.

Valdivia

Simposio; II International Symposium “Reconstructing Climate Variations in South America and the Antarctic Peninsula over the last 2000 years”; 2010

PAGES; Centro de Ingenieria de la Innovación, Facultad de Ciencias Forestales y Recursos Naturales, Universidad Austral de Chile

A new Holocene record from Laguna El Sosneado, in the upper Atuel River basin (34°47’S, 69°52’W; 2000 m asl), provides information on the environmental history of a region where little paleoenvironmental data is available and offers a comparison with other published records. Between 6400 and 1900 cal-yr-BP the pollen record shows the development of Andean-Patagonian shrub steppes dominated by Poaceae, Chenopodiaceae, Mulinum, Chuquiraga, Adesmia, Berberis, Asteraceae, Ephedra and Schinus that characterize the vegetation growing above 2200 m asl, suggesting wetter (~700 mm annual precipitation) and colder (~7.5°C annual temperature) than present conditions. During this interval, the high-resolution charcoal record suggests that fires were frequent. The highest fire activity between 2500 and 1900 cal-yr-BP is explained by a greater abundance of fine fuels as implied by the high values of grass/total charcoal proportions. In addition, an increment of Poaceae and Mulinum indicate a period of greater effective moisture. An abrupt change at 1900 cal-yr-BP towards more sparse vegetation similar to the lower belts of Patagonia-Monte steppes dominated by Neosparton, Asteraceae, Poaceae, Larrea, Prosopis, Prosopidastrum and Junellia indicate drier (~500 mm) and warmer (~9.5°C) than present conditions. Fire shows low frequency and low magnitude due to a lack of fuel presumably caused by the abrupt decrease of Mulinum, a fire-adapted cushion shrub, and Poaceae. The last 700 cal-yr-BP mark the development of the modern Patagonian steppes and semi-arid conditions (~600 mm and ~8°C) with the almost total absence of fire except for three events correlated with the LIA. Evidence of wet conditions in the Andean foothills during the middle Holocene contrasts with postulated arid conditions, especially in the western side of the Andes (37°-22°S). Our reconstructions agree with the onset of dry-wet periods recorded in northern-Patagonia, south-central Chile, and neoglacial advances documented in the area from 5500-4400 and 2500-2000 cal-yr-BP showing a strong relationship with the westerly dynamics.