Long term vegetation history in the Río Manso catchment area, Northern Patagonia. Pollen as proxy record

1. BIANCHI, M.M., WHITLOCK, C.; IGLESIAS, V. AND C. F. PÉREZ, C.F.

San Carlos de Bariloche

Simposio; Symposium: Palaeoenvironmental changes since the Last Glacial Maximum: patterns, timing and dynamics throughout the Southern Hemisphere. VI Southern Connection Congress; 2010

The Manso River originates in the El Manso Glacier of Cerro Tronador and discharges into the Pacific Ocean after flowing along 81 km on a mountain landscape. Because of major hydrological differences it is divided in: The Manso Superior, Medio and Inferior rivers. Pollen studies in this watershed allowed us to gain a better understanding of the vegetation history at different time scales in the region. Pollen transport over the Andes by trajectory analysis of air masses has been shown to occur in the entire watershed and pollen rain studies are in progress. Research in the Río Manso Superior watershed, included a pollen record from Lake Mascardi (41°08’S, 71° 34’ W, 775 m asl), extending back to the Late Glacial period. The pollen data show that forest diversification took place with amelioration of climatic conditions and the vegetation became more open during the Huelmo-Mascardi cold reversal. Ancient Nothofagus forest was replaced by mixed Nothofagus- middle Holocene, forest due to an increase in precipitation, and became denser under higher climate variability during the late Holocene. Statistical analyses of modern pollen from surface samples along an altitudinal transect from high- Andean to low Nothofagus forest support the interpretation of vegetation history. Preliminary results from a 7- m-long sediment core from Lake Huala Hué (41° 30’S -71° 30’ W, 849 m asl), Manso Medio river basin, show that Nothofagus dominates most of the sequence with highest values of Cupressaceae, probably Austrocedrus chlensis, after its expansion, ca. 5700 cal yrs B.P. The area exhibited high fire frequency during the last centuries (high resolution charcoal analysis in progress).