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18-04-2015, 03:09

Climatic Changes during the Final Pleistocene

The landscapes described above have changed relatively little since the beginning of the Holocene, that is, since 10 000 years ago. Paleoclimatic studies have nonetheless revealed a somewhat warmer and more humid period between approximately 8000 and 3000 BP, related to what is known as the Climatic Optimum. In contrast, major environmental modifications occurred at the end of the Pleistocene, between 14 000 and 10 000 BP. We will explore those that had a direct influence on the modes of human occupation.

In the high Andes, before 14 000 BP, and even during the last great glacial advance of the Quaternary between 21000 and 14 000 BP, the ice fields never formed an uninterrupted barrier. From Ecuador to northern Peru, where the altitude is largely compensated by the latitude, the ice-covered sectors remained separated from each other by basins or plateaus with more temperate climates. Only the central Andes of Peru, above 4000 m, were covered with ice. The Andes of Bolivia, northern Chile, and northwest Argentina remained free of ice except for a few isolated massifs above 4500 m. During this time, the high plateaus and intra-mountainous basins had open landscapes, which were usually treeless and, depending on the latitude and altitude, covered with prairies, savannas, deserts, or tundras. The eastern piedmont of the Cordillera was also covered with savannas, punctuated by a few wooded enclaves.

Beginning in 14 000 BP, the glaciers began to retreat. After the last short cold phase of the Late Glacial period, around 11 000/10 000 BP, the general climatic warming gradually leads to our current climatic conditions. Accompanied by the re-establishment of a seasonal rhythm of precipitations, this warming led to a general increase in vegetal cover at high altitudes. In the northern Andes, paramos developed, while the eastern piedmont was progressively invaded by tropical forest. In the Andes of Peru and Bolivia, the deglaciation cleared vast extensions of high plateaus where a climate less humid than that of the north favored the extension of vast carpets of puna and altiplano graminae. Further south, this rapid warming resulted in the extension of high altitude deserts, the Dry Puna and Salt Puna of Atacama and southern Bolivia.

Along the Pacific coast, the sea level during the last glacial maximum was around 100 m lower than it is today and the coastal plain was probably 2 times wider. Beginning in 12 000 BP, the sea level began to rise and coastal zones were gradually submerged. We must remember, however, that while the melting of Andean glaciers was rapid (a few centuries or even a few dozen years), that of the inlandsis glaciers extended over several thousands of years. For this reason, while the Andean glaciers attained their current limit everywhere around 10 000 BP, the level of the Pacific was still 50 m lower than its current level. This slow rise in sea level continued over thousands of years until around 6000 BP when it exceeded the present level by 2-4 m. This ‘transgression’, though compensated in part by the slow elevation of continental masses liberated from the weight of glaciers (isostasy), resulted in the submersion of all human occupations older than 6000 BP along the low coasts.

Though the climatic fluctuations that occurred from 14 000 to 10 000 BP led to only moderate landscape modifications, we can easily imagine that human occupations were largely dependent on them. At the time when the maximum extension of the glaciers stretched over vast cold and humid surfaces, the valleys and intra-mountainous basins of the lower altitudes remained sheltered and relatively dry. They thus constituted favorable zones for occupation by small hunter-gatherer groups, while the higher zones remained uninhabitable. During the phases of glacial regression, on the other hand, the increase in herbaceous vegetal cover at high altitudes contributed to the multiplication of faunal species, notably herbivores, cervidae, and camelidae. The vast open spaces of the high plateaus thus presented advantageous conditions for mobile hunter groups.



 

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