Palaeoenvironmental reconstruction of Late Glacial-Holocene environmental change for Patagonia, southern South America

Abstract

Patagonia is the only continental landmass to intersect the entire migratory track of the Southern Westerly Winds (SWWs), which are a component of the global atmospheric system that has governed the palaeo and modern climate of Southern South America between 30°S and 60°S. Palaeoenvironmental proxies can be used to determine past changes in the migration patterns of the SWW’s and how this migration effects the timing and nature of climatic changes during the Late glacial and Holocene. Three deep basin peat-sediment cores were taken from an extensive latitudinal transect (~47-55°S) on the eastern flanks of the Andean Cordillera in Patagonia. By reconstructing the latitudinal changes from the vegetation response to these migrating fronts the spatial and temporal shifts in the SWWs were determined. Palynological and lithostratigraphic evidence provided by records from Cerro Ataud (47°17’ S 72°39’ W), Lago Fox (53°52’S, 70°26’W) and Punta Burslem (54°54’ S, 67°57’ W) were correlated with other palaeoenvironmental data from proximal sites in central and southern Patagonia and constrained by radiocarbon dating and tephrochronology. The records indicate that deglaciation began sometime before c. 17 kcal yr BP at Pta Burslem, c. 15.7 kcal yr BP at Lago Fox and c. 13.4 kcal yr BP at Cerro Ataud all reflecting warmer interstadial temperatures in the Late glacial. A period of forest expansion by c. 11.5 kcal yr BP at Lago Fox, c. 10.3 kcal yr BP at Pta Burslem and c. 9.5 kcal yr BP at Cerro Ataud as a consequence of increased humidity from the poleward shift in the SWWs was followed by an arid phase and forest contraction between c. 6-9 kcal yr BP at all sites as the SWWs continued to migrate poleward. Arboreal cover increased again between c. 6.4-5 kcal yr BP in response to increasing humidity from an equatorward shift in the SWWs as global temperatures began a cooling trend in the Mid to Late Holocene. A period of climatic instability is then seen from c. 5 kcal yr BP to the present at all three sites as the SWWs shifted into their contemporary position of ~50°S. While the key findings reinforce a prevailing set of ideas about the movements of the SWWs, importantly this study identifies that the SWWs remained beyond the South American continent influencing the ocean-atmosphere system of the Southern Ocean for ~ 3000 years. This is a significant finding for future global warming scenarios.