¹Jasmijsn Van der Graaf, ²John F. Mustard, ¹Annemiek C. Waajen, ³Frank J.A. Van Ruitenbeek, ^4,5Christopher S. Romanek, ^1,4Mónica Sánchez-Román
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117262]
¹Geobiology Lab, Earth Sciences Department, Vrije Universiteit Amsterdam, De Boelelaan 1100, 1081HV Amsterdam, the Netherlands
²Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA
³Department of Applied Earth Sciences, Faculty of Geo-Information Science and Earth Observation, University of Twente, Drienerlolaan 5, 7500 AE Enschede, the Netherlands
⁴NASA Astrobiology Institute, USA
⁵Department of Earth and Environmental Sciences, Furman University, Greenville, SC, USA
Copyright Elsevier

Microbial activity plays a crucial role in the precipitation of carbonate minerals, mediated by bacterial cells and their secreted extracellular polymeric substances (EPS). Traditional detection of such biosignatures often requires invasive chemical treatments. This study explores the potential of Fourier Transform Infrared (FTIR) spectroscopy as a non-destructive tool to identify compositional features and microbial imprints in mixed-cation carbonates, providing a new pathway for remote sensing applications and in situ mineralogical studies. Carbonate samples from natural settings and laboratory experiments, under both biotic and abiotic conditions were analyzed to reveal their distinct spectral characteristics. The minerals studied include dolomite, siderite, ankerite, (hydro)magnesite, and various carbonate hydroxides, with varying amounts of the cations Ca2+, Mg2+ and Fe2+.
Distinct FTIR spectral characteristics were observed: dolomites, in particular, exhibited consistent clustering in overtone band positions around 2300 nm and 2500 nm. While this clustering was less apparent in other carbonate types, Fe2+ content could be reliably traced through a unique near-infrared absorption feature, whose intensity correlated with Fe2+ abundance following a square root function.
Despite the overlap of biosignature and mineral spectral features, specific markers emerged in biogenic samples. These included weak absorptions near 3310 nm (indicative of alkene bonds) and enhanced OH− bands around 1400 nm and 2760 nm, possibly related to phenols, alcohols, or structural water-components often associated with microbial EPS. FTIR spectroscopy is sensitive to trace amounts of water and organic compounds, making it a promising tool for evaluating precipitation conditions and the diagenetic history of mixed-cation carbonates.