actualité scientifique · salt lake called tauca which covered more than 50,000 sq. km, an area...
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The famous Salar de Uyuni and the salt crust (© IRD / D. Wirrmann)
At the foot of the Andes, a gigantic lake, Tauca, covered the Bolivian Altiplano during the last deglaciation. Using an original method developed from fossil micro-algae called diatoms, researchers from IRD, CNRS and Aix-Marseille University have recently shown the effect on the regional climate of the disappearance 14,000 years ago of this salt-water giant, 3,500 metres up in the mountains. The lake’s drying out also gave rise to the world’s largest salt crust (11,000 sq. km) which now covers the famous Uyani salt flats.
Key pointsDuring the last deglaciation, from 18,000 to 10,000 years ago, the Bolivian Altiplano was submerged by an enormous salt lake called Tauca which covered more than 50,000 sq. km, an area larger than Switzerland. Nowadays, the vast white desert of the Uyumi salt flats, the world’s largest salt reserve, testifies to its existence.
GlossaryIsotope: elements, such as oxygen, possess a number of stable isotopes, which differ by the number of neutrons they have. The result is various forms of molecules of differing weights. The isotopic composition is the relative quantity of these different molecules.
Andes: a giant paleolake in the land of glaciers
Scientific news Actualidad científica
Actualité scientifique
N° 484July 2015
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The last deglaciation in the Bolivian AndesIRD researchers and their partners from CNRS and Aix-Marseille University have recently shown the regional influence of the Tauca paleolake, which occupied the Bolivian Altiplano at the time of the last deglaciation. The phase within which this gigantic lake reached its maximum extent began 16,000 years ago. It then gradually dried up and disappeared some 2,000 years later.To study the lake’s possible influence over the region’s climate, the scientists reconstituted its isotopic composition by means of an original method making use of fossil micro-algae called diatoms.
Micro-algae as evidence of humidity conditions The amount of oxygen isotopes (δ18O) contained in these fossils provides evidence of the geochemical condition of the water in the lake in which the algae grew. This isotopic composition gives scientists an accurate indicator of temperatures and humidity conditions in the region at the time when the algae were alive. When rainfall increases and the lake level rises, the isotopic ratio of the oxygen in the water drops, the opposite being the case when rainfall declines.
Regional climate influenceThe researchers then turned their attention to changes in the lake’s isotopic composition which they reconstituted with another isotopic signal, recorded in an ice core extracted from the summit of Mount Sajama, overlooking Tauca’s former location. This ice core revealed, around 14,500 years back, a δ18O peak that was unusual compared to other ice records from the Andes. on the other hand, this peak was consistent with measurements taken from diatom fossils contained in the former lake’s sediment. This study therefore shows that snow samples from Sajama were apparently formed during this period, based on the mix between the
humidity in the atmosphere and that from the evaporation of the lake.
This finding suggests that in very specific cases like this, with the presence of a nearby lake, paleo-climatic records such as measuring precipitation from ice cores may be skewed by the local hydrological cycle, and should be interpreted with such an influence in mind.
Partners CNRS and Aix-Marseille Université.
ReferencesB. Quesada, Florence Sylvestre, Françoise Vimeux, J. Black, C. Paillès, C. Sonzogni, A. Alexandre, P-h. Blard, A.Tonetto, J.C Mazur, h. Bruneton. Impact of Bolivian paleolake evaporation on the δ18O of the Andean glaciers during the last deglaciation (18.5-11.7 ka): diatom-inferred δ18o values and hydro-isotopic modeling. Quaternary Science Reviews, 2015, 120, p. 93-106. doi:10.1016/j.quascirev.2015.04.022 Contacts
Florence Sylvestre, IRD researcherT. +33 (0)4 42 97 15 89 [email protected]
Benjamin Quesada, post-doctoral researcher at Karlsruhe Institute of TechnologyT. +49 (0) 8821 183 [email protected]
Centre européen de recherche et d’enseignement de géosciences de l’environnement (CeReGe)
Françoise Vimeux, IRD researcherT. +33 (0)1 69 08 57 71 [email protected]
Laboratoire hydroSciences Montpellier (hSM)
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