Ascotán and Carcote salt flats as sensors of humidity fluctuations and anthropic impacts in the transition zone of the Andean Altiplano

The Altiplano-Puna plateau is a climatic transition zone between the Atacama Desert, the aridest worldwide, and the Amazon basin. The salt flats of the Altiplano are hydrogeological and ecological systems highly dependent and sensitive to seasonal, interannual and inter-decadal variations in humidity; they may be markedly affected by anthropic activities. We focused on Ascotán and Carcote, two nearby salt flats located at more than 3,600 m of elevation at the border of Chile and Bolivia, to determinate the relationship between the depositional environments and recent hydrological conditions, which can be used as sensors of the particular climatic conditions of the Altiplano and anthropic activities in these systems. Results of analysis of sediment properties (mineralogical, geochemical and magnetic), the water (elemental composition) and diatom communities of the different springs in the salt flats showed that the water and sediments of Ascotán and Carcote salt flats were heterogeneous in granulometric, chemical, mineralogical and magnetic grain composition, both intra- and inter-salt flat. The content of saline facies tended to increase in zones furthest from the edge and close to the depocenter of the basin, whose sediments were composed mainly of finer size grains. Diatom diversity and species richness differed between salt flats, which were associated with characteristics of the brine composition, grain size and magnetic properties and were mostly affected by local abiotic factors of each spring. Four sub-environments were identified based on the variables measured: alluvial, marsh, lacustrine and evaporitic, mainly defined by the recharge of water input dominated by summer rainfalls and snow melt. Our results suggest that Ascotán and Carcote salt flats constitute excellent sensors of the air moisture from the Amazon Basin, both current and through the Last Glacial Maximum and the Holocene. Therefore, further studies using Ascotán and Carcote as model systems may be focused on identifying hydro-geo-ecological changes in millennia-term variability of humid periods, in addition to short-term pressure from mining activity.