SOUTH AMERICAN MAJOR SYSTEMS IN THE LAST EXTREME CLIMATES

Climatic parameters of both extreme conditions (LGM and Hypsithermal) in South America can be reconstructed wih a reasonable certitude by using of a few key indicators. According to the available information, climatic belts migrated 5 to 10 degrees of latitude TO THE NORTH during the LGM, with a general lowering of temperature. At the Hypsithermal, climatic belts shifted SOUTHWARD, occurring a dry climate in the north of the continent and higher humidity in the south. Such reconstructions are validated by the following: - At present, the northern limit of the Westerlies is located at 40°S. At LGM the wind belt migrated up to 30/35°S, feeding glaciars in Central Chile and Argentina. A similar shifting of the trade-winds to the north can be deduced from data on the northern Andes and the Caribbean coast. During the Hypsithermal, the Equatorial Easterlies migrated approximately 10 degrees to the south in NE Brazil, and the arid belt of the Caribbean coast shifted to the Llanos del Orinoco region. Consequently, the Pampean climate migrated 5 degrees to the south in Patagonia, pushing the Westerlies poleward. - Marine currents show a marked asymmetry along the coasts of South America. The same pattern occurred during the Quaternary. The cold/warm front is located at present at 35°S. During the LGM, sediments originated in the Río de la Plata (identified by its illitic composition) reached the latitude of 22°S. Conversely, the front advanced to the south up to 40/42°S in the Hypsithermal. By using an analogy with El Niño conditions, we assume that the Humboldt current retreated from the Equator to 10°S in the Hypsithermal. The eolian transport of sediment at the LGM was widespread in South America, marking an advance of the Patagonian climate of more than 1,000 km to the northeast. In NE Brazil, succesive eolian formations were sedimented by the SE trade-wind. An anticiclonic circulation of such winds formed dune fields at the foot of the Andes in Bolivia and Paraguay. Lake levels were in general low in South America during the LGM, except in Bolivia, Chile and west Argentina, with a tendency to conditions oposite to the former ones in the middle Holocene.