Palaeohydric balance variations in eastern Andean environments in southern Patagonia (48°–52.5° S): Major trends and forcings during the last ca. 8000 cal yrs BP

Abstract

The core of the storm track flow intersects the landmass of Southern Patagonia providing a unique opportunity for palaeo-reconstructions. Most of the palaeo-reconstructions are based on records from sites where the relationship between precipitation and wind flow intensity, can be reconstructed from the impact on vegetation communities. Seven sites were selected for this study. The importance relies on their location in relation to vegetation communities; two sites lie within forest communities, two are from the forest-steppe ecotone and the other three from steppe communities in Southern Patagonia, Argentina, between 48° and 52.5° S and between 70° and 72° W. To compare the past palaeohydric balance based on the seven pollen records from these different vegetation communities along the precipitation gradient, we constructed a Palaeohydric Balance Index (PBI). The PBI is based on the water requirement of the main plant taxa represented by the pollen types analyzed in the records. The information provided by this index improves the understanding of the hydric balance variability in relation to the storm track behavior. During the last 8000 cal yrs BP we observed out-of-phase behavior in PBI variations between forest, forest-steppe ecotone and steppe PBIs, a greater amplitude of forest versus steppe environments and low amplitude of the forest-steppe ecotone variability. This out-of-phase behavior appears to have been replaced by in-phase palaeohydric changes between 700 and 500 cal yrs BP interpreted as related to an equatorward migration of the storm tracks.