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, M.A.; BAMONTE, F.P.; ECHEVERRÍA, M.E.

Medellín

Simposio; 3rd International Symposium. Climate change and human impact in Central and South America over the last 2000 yeras. Observations and Models; 2014

LOTRED-SA

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 evidences from past paleoenvironmental changes have been recorded with accurate chronological control from lakes and peat-bogs of forest and steppe communities between 36ºS and 52ºS. Vegetation patterns in Patagonia responds mainly to the west-east precipitation gradient at regional scale. Meanwhile at local scale, understanding individual species responses to local humidity patterns is extremely usefull to improve past vegetation dynamics related to past climate variability. Also, the comparison between current fire behaviour through different Patagonian communities and past charcoal records would improve paleoclimate variability inferences during the last 1500 years. During these work 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- ca. 800 cal yrs BP, paleovegetation indexes and charcoal records suggest dense humid forest communities south to 45º 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-like-conditions where the westerlies intensifies and moves southward. Also during SAM positive fase, the westerlies moves southward decreasing Pacific precipitation northward to 48ºS and favouring fire activity in northern Patagonia. After 700 cal yrs BP, paleoenvironmental conditions turns to drier ones at southern forest communities 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 equatoward displacement of the westerlies and the Southern Pacific High associated to an increase on El Niño frequency between 800-300 cal yrs BP. The higher frequency of the formation of temporary high pressure centers southward to 40ºS during this period may block the westerlies circulation at southwestern Patagonia. The comparison of recently published pollen and charcoal records suggest an antiphase behaviour 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 stalagmites studies carried out between 41- 53ºS.