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
International audience During the last deglaciation, the Bolivian Altiplano (15e23 S, 66e70 W) was occupied by paleolake Tauca covering, at least, ~51,000 km 2 at its maximum highstand between 16.5 and 15 ka. Twenty-five hundred years later, after a massive regression, a new transgressive phase, pro...
Published in: | Quaternary Science Reviews |
---|---|
Main Authors: | , , , , , , , , , , |
Other Authors: | , , , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2015
|
Subjects: | |
Online Access: | https://hal.science/hal-01909526 https://hal.science/hal-01909526/document https://hal.science/hal-01909526/file/Quesada%20et%20al.,%202015.pdf https://doi.org/10.1016/j.quascirev.2015.04.022 |
Summary: | International audience During the last deglaciation, the Bolivian Altiplano (15e23 S, 66e70 W) was occupied by paleolake Tauca covering, at least, ~51,000 km 2 at its maximum highstand between 16.5 and 15 ka. Twenty-five hundred years later, after a massive regression, a new transgressive phase, produced paleolake Coi-pasa, smaller than Tauca and restricted to the southern part of the basin. These paleolakes were overlooked at the west by the Sajama ice cap. The latter provides a continuous record of the oxygen isotopic composition of paleo-precipitation for the last 25 ka. Contemporaneously to the end of paleolake Tauca, around 14.3 ka, the Sajama ice cap recorded a significant increase in ice oxygen isotopic composition (d 18 O ice). This paper examines to what extent the disappearance of Lake Tauca contributed to precipitation on the Sajama summit and this specific isotopic variation. The water d 18 O values of paleolakes Tauca and Coipasa (d 18 O lake) were quantitatively reconstructed from 18.5 to 11.7 ka based on diatom isotopic composition (d 18 O diatoms) and ostracod isotopic composition (d 18 O carbonates) retrieved in lacus-trine sediments. At a centennial time scale, a strong trend appears: abrupt decreases of d 18 O lake during lake fillings are immediately followed by abrupt increases of d 18 O lake during lake level stable phases. The highest variation occurred at ~15.8 ka with a d 18 O lake decrease of about ~10‰, concomitant with the Lake Tauca highstand, followed ~400 years later by a 7‰ increase in d 18 O lake. A simple hydro-isotopic modeling approach reproduces consistently this rapid "decreaseeincrease" feature. Moreover, it suggests that this unexpected re-increase in d 18 O lake after filling phases can be partly explained by an equilibration of isotopic fluxes during the lake steady-state. Based on isotopic calculations during lake evaporation and a simple water stable isotopes balance between potential moisture sources at Sajama (advection versus lake evaporation), we show that total ... |
---|