Biogeochemical processes controlling oxygen and carbon isotopes of diatom silica in Late Glacial to Holocene lacustrine rhythmites

Armand Hernández, Roberto Bao, Santiago Giralt, Philip A. Barker, Melanie J. Leng, Hilary J. Sloane, Alberto Sáez

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

Biogeochemical cycles and sedimentary records in lakes are related to climate controls on hydrology and catchment processes. Changes in the isotopic composition of the diatom frustules (δ18Odiatom and δ13Cdiatom) in lacustrine sediments can be used to reconstruct palaeoclimatic and palaeoenvironmental changes. The Lago Chungará (Andean Altiplano, 18°15′S, 69°10′W, 4520masl) diatomaceous laminated sediments are made up of white and green multiannual rhythmites. White laminae were formed during short-term diatom super-blooms, and are composed almost exclusively of large-sized Cyclostephanos andinus. These diatoms bloom during mixing events when recycled nutrients from the bottom waters are brought to the surface and/or when nutrients are introduced from the catchment during periods of strong runoff. Conversely, the green laminae are thought to have been deposited over several years and are composed of a mixture of diatoms (mainly smaller valves of C. andinus and Discostella stelligera) and organic matter. These green laminae reflect the lake's hydrological recovery from a status favouring the diatom super-blooms (white laminae) towards baseline conditions δ18Odiatom and δ13Cdiatom from 11,990 to 11,530cal years BP allow us to reconstruct shifts in the precipitation/evaporation ratio and changes in the lake water dissolved carbon concentration, respectively. δ18Odiatom values indicate that white laminae formation occurred mainly during low lake level stages, whereas green laminae formation generally occurred during high lake level stages. The isotope and chronostratigraphical data together suggest that white laminae deposition is caused by extraordinary environmental events. El Niño-Southern Oscillation and changes in solar activity are the most likely climate forcing mechanisms that could trigger such events, favouring hydrological changes at interannual-to-decadal scale. This study demonstrates the potential for laminated lake sediments to document extreme pluriannual events.

Original languageEnglish (US)
Pages (from-to)413-425
Number of pages13
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume299
Issue number3-4
DOIs
StatePublished - Jan 15 2011

Bibliographical note

Copyright:
Copyright 2011 Elsevier B.V., All rights reserved.

Keywords

  • Andean Altiplano
  • Carbon isotopes
  • Diatoms
  • ENSO
  • Lacustrine sediments
  • Oxygen isotopes

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