Dryness and social disruption in dry intermountaneous valleys of northwest Argentina, during the medieval warm epoch

SAYAGO, J. M.; M.M. SAMPIETRO VATTUONE; M.A. CARIA; M.M. COLLANTES

Lisboa. Portugal

Congreso; Colloquia Climatic Change and Social Evolution in the Arid Lands During the Holocene; 2006

During the Medieval Warm Epoch in Greenland, Iceland and portions of northern Europe temperatures began to rise around AD 800 until  AD 1300 with a cool interlude between AD 1050 and 1150 (Lamb 1965, 1977). Authors as Stine 1998, Hodel et al. 1995, Abbot et al. 1997 and Binford et al. 1997 demonstrate the influence of highly dryness in social disruption of human occupations, in Yucatan Peninsula, South-tropical Andes and Patagonia, during the medieval times. This work describe the influences of  extreme dry climatic conditions in the abandonment of long-occupied sites of agrarian cultures in the Tafí Valley -at the western side of the pre-Andean ridges-  and it’s possible migration to the more humid eastern regions during the Medieval Warm Epoch. The Tafí culture flourished from around 2500 AP up to 1500 AP when a progressive dryness would explain the abandonment of the occupations from the valley bottom with a migration toward the north and north-eastern that culminates around 800 AP. The palinological reconstruction (Garralla, 1999) points out the change from coverage similar to the present dry-wet sub-tropical forest to the typical xerophytic vegetation of “Espinal or Monte” around 1200 AD contemporary with the last Tafi occupations. In the Trancas valley at eastern side of pre-Andean ridges under wetter climatic conditions only pure remains of Candelaria (a typical culture of the dry-wet sub-tropical forest) are described before 900 AD. After that, Candelaria culture appears associated with Santa Maria handiworks (Berberian 1977, Caria 1999) which would suggest the migration of people from the arid western valleys (Valles Calchaquíes). Meggers (1994) suggested a relationship between Mega-Niños (ENSO) and dryness in several sites of Amazonia and Perú during the last two millennia. In addition, during the last century (Sayago et al. in press) demonstrated the relationship between El Niño face of ENSO and extreme dryness in north west of Argentina. The weakness of the South Atlantic anticyclone (influencing the weakness of trade winds over the South Paciphic), in parallel with a boreal migration of ITCZ, would explain the South Hemisphere dryness and cooling during the Medieval Epoch. Within a global perspective the contrast between temperature rise in northern Europe and Greenland and the dryness and cooling in the South would allow to expeculate with a climatic scenario similar to the bipolar sea sow.