Eastern Andean environmental and climate synthesis for the last 1500 years BP from terrestrial pollen and charcoal records of Patagonia

SOTTILE, G.D., MANCINI, M.V., MARCOS, A., BAMONTE, F.P, ECHEVERRÍA, M.E.

Simposio; LOTRED-Climate change and human impact in Central and South America over the last 2000 years, Observations and Models; 2014

Since the last 10 years there have been major improvements on the interpretation of terrestrial pollen and charcoal records from the Eastern side of the Patagonian Andes. New evidence from past paleoenvironmental changes have been recorded with accurate chronological control from lakes and peatbogs of forest and steppe communities between 36°S and 52° S. Vegetation patterns in Patagonia respond mainly to the west-east precipitation gradient at a regional scale. Meanwhile at a local scale, understanding individual species responses to local humidity patterns is extremely useful to improve the reconstruction of past vegetation dynamics related to past climate variability. Also, the comparison between current fire behavior through different Patagonian communities and past charcoal records would improve paleoclimate variability inferences during the last 1500 years. During this study paleovegetation/water balance indexes were performed at 7 sequences of pollen records from forest and steppe communities at the eastern side of the Patagonian Andes. Paleo-indexes patterns were compared to other Patagonian lake and peat-bog sequences, including pollen and charcoal records published recently. Between 1500 and ca. 800 cal yrs BP, paleovegetation indexes and charcoal records suggest dense humid forest communities south to 45° S. The opposite signal is recorded in northern forest communities, suggesting open forest communities and high fire activity. Meanwhile steppe environments show low vegetation cover and low fire activity probably linked to xeric conditions. These paleovegetation and paleofire patterns may respond to La Niña-likeconditions where the westerlies intensify and move southward. Also during SAM positive phase, the westerlies move southward decreasing Pacific precipitation northward to 48°S and favouring fire activity in northern Patagonia. After 700 cal yrs BP, paleoenvironmental conditions turn to drier ones at southern forests and wetter conditions at northern forest communities. Steppes environments present wetter conditions during LIA than during MCA. These patterns may respond to a weakening and equatorward displacement of the westerlies and the Southern Pacific High associated to an increase in El Niño frequency between 800 and 300 cal yrs BP. The higher frequency of the temporary high pressure centers development southward to 40°S during this period may block the westerlies circulation at southwestern Patagonia. The comparison of recently published pollen and charcoal records suggest an antiphase behavior between north and southern Patagonia during the last 1500 yrs BP. This antiphase is also registered between forest and steppe communities of southern Patagonia. Our interpretations agreed with other marine and speleotherms studies between 41 and 53°S.