1,3,4,5,- 1Institute of Geology and Mineralogy, University of Cologne, Cologne, Germany
- 2Departamento de Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile
- 3Geochemistry and Isotope Biogeochemistry Group, Department of Marine Geology, Leibniz Institute for Baltic Sea Research (IOW), Warnemünde, Germany
- 4Marine Geochemistry, University of Greifswald, Greifswald, Germany
- 5Interdisciplinary Faculty, University of Rostock, Rostock, Germany
The Atacama Desert contains the largest natural nitrate accumulations on Earth. Yet, the processes controlling their formation and redistribution remain debated, particularly for nitrate veins hosted in bedrock. In this study, we combine field observations with chemical and stable isotope analyses (δ18O, Δ17O, δ15N) of nitrate from all major deposit types across the Atacama nitrate provinces. All nitrate occurrences display large positive Δ17O values (+13 to +22‰) and elevated δ18O (+43 to +65‰), confirming a unanimous atmospheric origin via ozone-driven photochemical oxidation of NOx.
Vein-hosted nitrates in volcanic and sedimentary rocks show suppressed Δ17O and δ18O values trending toward fossil hydrothermal waters, indicating partial oxygen isotope exchange during interaction with hot, saline, acidic fluids. Field relationships, fault-controlled mineralization, rhyolitic exsolution textures, and sulfate sulfur isotopes independently confirm hydrothermal dissolution, transport, and reprecipitation of originally atmospheric nitrate.
These results define a two-stage geological cycle: long-term atmospheric deposition, groundwater transport, and evaporative concentration under hyperaridity, followed by tectonically driven hydrothermal recycling linked to Andean magmatism. This two-mechanism framework reconciles the isotopic, mineralogical, and spatial diversity of nitrate deposits, demonstrating that the Atacama Desert records a coupled atmospheric–hydrothermal cycle linked to the tectonic and magmatic evolution of the central Andean margin, and providing a template for other nitrate-bearing deserts on Earth and potentially on other planets.
Nitrate deposit δ15N = −8 to +4‰ are slightly higher than in atmospheric nitrate and overlap with the Atacama soil nitrate profile compositions, but in contrast show a positive correlation with δ18O. This excludes humidity driven microbial denitrification and gaseous N loss as a major driver for local secondary composition contrasts.
How to cite: Riffo Contreras, C., Chong, G., Klipsch, S., E. Böttcher, M., Davies, A., and Staubwasser, M.: The Geologic Super-Cycle of Chilean Nitrate Deposition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11165, https://doi.org/10.5194/egusphere-egu26-11165, 2026.
