CLIMATIC VARIATIONS IN THE ARGENTINE PLAINS DURING THE LAST 18,000 YEARS

The last deglacial hemicycle was characterized by a general increase i n temperature and precipitation in the region, with a few significant departures from this general trend. The present NE-SW climatic gradien t was maintained throughout the entire period, except in the Upper Hol ocene. The following sequence of events is apparent if the present cli mate is taken as a reference base: (a) 18,000-8500 yr B.P.: Arid and c ool, with aeolian sand and loess deposition. Patagonian fauna. Climati c isolines (temperature, precipitation, etc.) were located some 750 km northeast of their present positions. (b) 8500-3500 yr B.P.: Humid su btropical, with Brazilian fauna. Pedogenesis and fluvial dynamics. Cli matic limits migrated about 800/900 km southwest of their former posit ions. (c) 3500-1000 yr B.P.: Dry subtropical; aeolian dynamics. The no rmal latitudinal climatic gradient was interrupted by the occurrence o f an anticyclonic centre, which stabilized the climate over an area of some 1,600,000 km2. (d) 1000 yr B.P.-Little Ice Age: Climate was simi lar to the present one over much of the plains, but the northeastern e xtremity was warmer. (e) Little Ice Age: Climatic deterioration in the southern belt was characterized by generalized aeolian activity and m igration of isolines more than 150 km to the northeast in that area. ( f) Present climate: 19th and 20th centuries. Subtropical, humid in the east and dry in the west.