Actualité scientifique
Actualidad científica
Scientific news
N° 484
July 2015
Andes: a giant paleolake in the land of
glaciers
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 points
During 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.
Glossary
Isotope: 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.
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 influence
The 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.
Coordination
Gaëlle Courcoux
Information and Culture
Department
T. +33 (0)4 91 99 94 90
[email protected]
www.ird.fr/la-mediatheque
Partners
CNRS and Aix-Marseille Université.
References
B. 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 (18.511.7 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
Media Contact
Cristelle DUOS
T. +33 (0)4 91 99 94 87
[email protected]
Contacts
Florence Sylvestre, IRD researcher
T. +33 (0)4 42 97 15 89
[email protected]
Benjamin Quesada, post-doctoral researcher
at Karlsruhe Institute of Technology
T. +49 (0) 8821 183 188
[email protected]
Centre européen de recherche
d’enseignement
de
géosciences
l’environnement (CEREGE)
et
de
Françoise Vimeux, IRD researcher
T. +33 (0)1 69 08 57 71
[email protected]
Indigo, IRD Photo Library
Daina Rechner
Tél. : +33 (0)4 91 99 94 81
[email protected]
www.indigo.ird.fr
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© IRD/DIC, Mars 2015 - Conception et réalisation graphique : L. CORSINI
The last deglaciation in the Bolivian
Andes
IRD 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.
Contacts