Tracing the water cycle in the Atacama Desert using water isotopes (δ2H, δ17O, δ18O) and pedogenic salt distributions

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Title:Main Title: Tracing the water cycle in the Atacama Desert using water isotopes (δ2H, δ17O, δ18O) and pedogenic salt distributions
Description:Abstract: Stable isotope ratios of water (18O/16O and 2H/1H) are widely used in hydrological studies. In contrast to classic tracers (δ2H–δ18O, d-excess), the triple oxygen isotope system (δ17O–δ18O, 17O excess) is virtually insensitive to changes in temperature and salinity, providing additional information on processes in the hydrological cycle. Large isotope effects associated with evaporation occur mainly in response to humidity. These isotope effects can be quantified by the classic Craig-Gordon evaporation model. The main objective of this thesis is to investigate the potential of combined analysis of hydrogen (2H/1H) and triple oxygen (18O/17O/16O) isotopes of structurally bonded water of gypsum (CaSO4 · 2H2O) to quantitatively estimate paleo-humidity and reconstruct past changes in the climatic conditions of the presently hyperarid Atacama Desert. The first study serves to investigate recent dynamics in the isotopic composition of lake water in the complex hydrological system of the Salar del Huasco, Altiplano, Chile, that receives inflow from multiple sources and is affected by seasonal variability in precipitation, temperature and relative humidity. Isotope analyses of lakes and ponds from the Salar del Huasco revealed that their hydrological balance is mainly controlled by evaporation and recharge. Inflow from multiple sources and temporal variability in their isotopic composition lead to scattering of pond data along the evaporation trendline predicted by the Craig-Gordon model. Sporadic flooding events after heavy rainfalls can provoke significant mixing and lead to the emergence of non-recharged lakes. Evaporation without recharge as well as mixing processes can be identified by triple oxygen isotope analysis. The potential occurrence of episodic mixing processes, e.g. due to frequent flooding, should be taken into account in paleo-applications. The second study presents first results of isotope analyses of structurally bonded water of gypsum from paleo-lake deposits in the Atacama Desert. The isotopic compositions of analyzed samples fall on distinct evaporation trends indicating the preservation of the primary isotope signal of paleo-lake water. A Craig-Gordon model together with a Monte Carlo simulation was used to determine the relative humidity that best fit the isotope data in both d-excess vs δ18O space and 17O-excess vs δ18O space. The model output humidity is less affected by changes in the isotopic composition of source water and atmospheric vapor, however, can strongly depend on the selected wind induced turbulence coefficient and the limitations of the recharge rate (E/I). The model provides reasonable humidity values if the input parameters are set within ranges reasonable for the site. Results imply humid conditions in the northern Atacama Desert about 3.5 million years ago that may have been facilitated by permanent El Niño like conditions in the Early Pliocene Warm Period (4.5 – 3.0 Ma). The third study aims to improve the understanding of soil formation and secondary redistribution and transformation processes of evaporites in Atacama Desert soils, which is crucial for the interpretation of isotopic compositions of structurally bonded water of pedogenic gypsum. In this study, thin surface crusts, powdery surface material and subsurface concretions from up to 40 cm depth were sampled along several latitudinal transects between 19.5–25°S and 68.5–70.5°W. Results imply that long-term aridity gradients, sources and secondary mobilization processes control the spatial distribution of highly soluble salts – chlorides and nitrates – as well as gypsum and anhydrite in Atacama Desert soils. Hyperaridity is most persistent between 19-22°S. Exceptionally high chloride contents below the altitude of the atmospheric temperature inversion layer (< 1200 m) as well as Na/Cl ratios of 0.83 – close to the global sea water ratio of 0.86 – suggest sea spray as the primary source of halite. Generally, gypsum and anhydrite are the major minerals in Atacama Desert soils. The association of high anhydrite abundances with high chloride and nitrate contents indicate that anhydrite is a secondary product of dissolution-reprecipitation reactions in highly saline brines. This thesis expands our knowledge of processes controlling the isotopic composition of structurally bonded water of lacustrine and pedogenic gypsum. The results contribute to the development of a powerful isotope tool that can allow for a quantitative reconstruction of past climatic mean states in the Atacama Desert.
Responsible Party
Creator:Claudia Voigt (Author)
Publisher:Universitäts- und Stadtbibliothek Köln
Publication Year:2020
CRC1211 Topic:Climate
Related Subproject:D3
Subjects:Keywords: Stable Isotope Geochemistry, Paleoclimate Proxies
Geogr. Information Topic:Environment
File Details
Data Type:Text - Article
File Size:5.3 MB
Date:Submitted: 23.03.2020
Mime Type:application/pdf
Data Format:PDF
Download Permission:Only Project Members
General Access and Use Conditions:According to the CRC1211DB data policy agreement.
Access Limitations:According to the CRC1211DB data policy agreement.
Licence:[CRC1211DB] Data policy agreement
Specific Information - Publication
Publication Status:Accepted
Review Status:Not peer reviewed
Publication Type:Article
Article Type:Electronic
Source:Universitäts- und Stadtbibliothek Köln
Number of Pages:149 (1 - 149)
Metadata Details
Metadata Creator:Claudia Voigt
Metadata Created:11.08.2020
Metadata Last Updated:27.01.2022
Funding Phase:1
Metadata Language:English
Metadata Version:V50
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