Siliceous speleothems are cave formations found in lava tubes composed of minerals deposited by volcanic activity. These speleothems are important to determine the timing and intensity of past volcanic eruptions, as well as assessing the environment conditions [1]. The recognition of biosignatures (organic compounds or microorganisms) preserved in speleothems is also relevant for studying life in extreme environments and valuable for astrobiology. To conduct these investigations, the use of cutting-edge analytical techniques based on molecular characterization of cave samples are crucial to accurately analyze a number of different organic compounds that are generally found at very low abundance. One of the most promising techniques is analytical pyrolysis (Py) coupled to exact-mass spectrometry (Py-GC/Q-TOF). Analytical Py is the thermochemical decomposition of organic materials (OM) at elevated temperatures in the absence of oxygen. The products of Py are amenable to chromatographic separation which, when combined with appropriate detectors, yields valuable fingerprint information about the composition and molecular structure of complex mixtures of natural and synthetic macromolecules [2,3]. Analytical Py poses several advantages over other techniques for OM characterization: minimal or no sample preparation needed, the small sample size required, and the ability to detect and characterize a wide variety of organic materials in a single analysis, including recalcitrant and low solubility organic forms [4]. Therefore, this technique is convenient for relatively rapid analyses of scarce or unique organic samples such as those found in extreme environments and Mars analogues s [1,5]. Ultra-high resolution analytical pyrolysis (UH-Py) usually allows the identification of thousands of distinct organic molecules per sample, without any pre-treatment. However, this overwhelming number of chemical structures made the individual study of the identified compounds almost impossible and not feasible. Therefore, it is desirable to develop novel graphical-statistical tools to help identifying the main chemical and biogenic families found in a sample [6,7], as well as to study the alterations and adaptation of microorganisms to environmental or anthropogenic factors [5,8]. In this communication, the advantages of the combination of UH-Py technique with multivariate statistical analysis and graphic-statistical tools will be presented as an innovative strategy for unsupervised classification and visual analysis of organic matrices preserved in siliceous speleothems from different lava tubes from La Palma (Canary Island), Easter Island and Galapagos Islands (Fig. 1). The combination of both analytical techniques allows the identification of biosignatures of life forms (microorganisms), as well as biomarkers of paleoenvironmental and anthropogenic alterations (e.g., wildfires, ecocide).

Acknowledgments: The Spanish Ministry of Science and Innovation from the Spanish State Agency (AEI) is acknowledged for funding projects TUBOLAN (PID2019-108672RJ-I00) and EQC2019- 005772-P and the Portuguese Foundation for Science and Technology (FCT) for MICROCENO project (PTDC/CTA-AMB/0608/2020). The Spanish National Research Council (CSIC) is also acknowledged for the intramural project PIE_20214AT021. N.T.J-M. and A.Z.M thank the Ramón y Cajal research contracts (RyC2021-031253-I and RYC2019-026885-I, respectively). L. M. San Emeterio thanks MICIU for FPI research grant (BES-2017-07968).

References: [1] Miller A. Z. et al. (2016) J. Chrom. A, 1461, 144–152. [2] González-Pérez J. A. et al. (2015) J. Chrom. A, 1388, 236–243. [3] San-Emeterio L. M. et al. (2021) Appl. Sci. 11, 6684. [4] Quénéa K. et al. (2006) J. Anal. Appl. Pyrolysis, 76, 271–279. [5] Miller A. Z. et al. (2022) IScience, 25, 104556. [6] Jiménez-Morillo N. T. et al. (2016) Catena, 145, 266– 273. [7] Jiménez-Morillo N. T. et al. (2022) Sci. Total Environ. 817, 152957. [8] Miller A. Z. et al. (2020) Sci. Total Environ. 698, 134321

Resumen de la comunicación oral presentada en el 4th International Planetary Conference that will be held in Lanzarote from the 4th to the 7th of May 2023

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