A tough travesia: mobility among Late Holocene Patagonian hunter-gatherers through stable oxygen isotopes in enamel and water sources

Central-eastern North Patagonia is characterized by a severe environmental fragmentation due to the scarce and heterogeneous distribution of fresh water. The main local wet zones, the Negro and Colorado river valleys in the North and the Somuncurá Foothills in the South are separated by a large and harsh dry land, the travesía. In this paper, we assess the effects of this environmental fragmentation in the mobility of the Late Holocene huntergatherers through the analysis of the stable isotopes of oxygen in both enamel and water sources. We analyzed the δ18O of the enamel carbonate of 64 human teeth from 42 individuals from the Negro River valley (n = 30) and the Somuncurá Foothills (n = 12) and transformed them into drinking water values (δ18Odw) to be compared with an oxygen water baseline built from the most important surface water sources of the area. Our results show variable mobility, but they also highlight two trends regarding the direction of the movement. First, people buried at the Negro River valley seem to have consumed more regularly water from the Colorado River in the North than from other water sources located farther south (e.g. Somuncurá Foothills). Second, the δ18Odw values from the Somuncurá sample show east-to-west prevalent mobility along the foothills, far from the northern water sources (e.g. Colorado River). This weak connectivity between the northern and the southern parts of the study area (Negro and Colorado river valleys and Somuncurá Foothills) is probably related to the harsh environmental constraints imposed by the travesía. Our isotopic results in conjunction with the available archaeological and ethnohistorical data indicate that this large dry land acted as a marginal space in terms of human exploitation and that it certainly influenced human mobility