Abstract
AbstractVarious paleoclimatic records have been used to reconstruct the hydrologic history of the Altiplano, relating this history to past variability of the South American summer monsoon. Prior studies of the southern Altiplano, the location of the world’s largest salt flat, the Salar de Uyuni, and its neighbor, the Salar de Coipasa, generally agree in their reconstructions of the climate history of the past ∼24 ka. Some studies, however, have highly divergent climatic records and interpretations of earlier periods. In this study, lake-level variation was reconstructed from a ∼14-m-long sediment core from the Salar de Coipasa. These sediments span the last ∼40 ka. Lacustrine sediment accumulation was apparently continuous in the basin from ∼40 to 6 ka, with dry or very shallow conditions afterward. The fossil diatom stratigraphy and geochemical data (δ13C, δ15N, %Ca, C/N) indicate fluctuations in lake level from shallow to moderately deep, with the deepest conditions correlative with the Heinrich-1 and Younger Dryas events. The stratigraphy shows a continuous lake of variable depth and salinity during the last glacial maximum and latter stages of Marine Oxygen Isotope Stage 3 and is consistent with environmental inferences and the original chronology of a drill core from Salar de Uyuni.
Highlights
The Altiplano is a large, endorheic basin located between the Cordilleras Oriental and Occidental of the tropical Andes
The most notable feature of the Salar de Coipasa record is the continuous presence of lacustrine sediments in the basin from ∼40,000 to 5500 cal yr BP, with no evidence of complete desiccation in that interval
We rely primarily on diatom assemblages and carbon isotopic composition of organic carbon to form our inferences about lake level
Summary
The Altiplano is a large, endorheic basin located between the Cordilleras Oriental and Occidental of the tropical Andes. Scientific investigations in the region reported on a series of carbonate benches (formed in shallow water as algal bioherms or “tufas”) above the plain of Salar de Uyuni and Salar de Coipasa, as well as elevated deposits above the shoreline of modern Lago Poopó and Lake Titicaca. These were considered evidence of ancient lakes much larger than those of today (Forbes, 1861; Agassiz and Garman, 1876; Musters, 1877; Minchin, 1882; Pompecki, 1905; Bowman, 1914). Multiple studies have explored the timing of long-term hydrologic change based on examination of the paleoshoreline deposits (Servant, 1977; Rondeau, 1990; Risacher and Fritz, 1991; Bills et al, 1994; Sylvestre et al, 1999; Placzek et al, 2006) and sediment cores from Lake Titicaca and Salar de Uyuni (Wirrmann and Mourguiart, 1995; Baker et al, 2001a, 2001b; Fornari et al, 2001; Fritz et al, 2004, 2007) and related reconstructions of regional hydrologic variation to processes at local to global scales. Baker et al (2001a, 2001b) hypothesized that regional precipitation variation, associated with the South American summer monsoon (SASM), was linked to variation in North Atlantic sea-surface temperature (SST) gradients at multiple temporal scales, a conclusion supported by more recent stratigraphic and modeling studies (Blard et al, 2011; Placzek et al, 2013)
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