The analytical potential of Femtosecond Laser-Induced Breakdown Spectroscopy (fsLIBS) for determination of trace elements in speleothems

The incorporation of trace elements into speleothems, either as impurities or as constituents of the crystal lattice structure, is significantly influenced by the hydrochemistry and environmental changes within and around caves. This study investigates the potential of Femtosecond Laser-Induced Breakdown Spectroscopy (fs-LIBS) to identify the spatial distribution and temporal variation of elemental ratios within a speleothem (DH-2) collected from Dharamjali Cave in the central Himalaya, India. We present a comprehensive methodology and experimental techniques to highlight the advantages of utilizing LIBS in speleothem research. The fs-LIBS analyses provide valuable insights into the distribution of trace elements, namely, magnesium (Mg), strontium (Sr), silicon (Si), aluminum (Al), potassium (K), and sodium (Na). Specifically, our study focuses on identifying pronounced variations in the Mg/Ca and Sr/Ca ratios along the growth axis of the DH-2 speleothem. These trace element variations exhibit consistent patterns that align with the stable isotope (delta 13C and delta 18O) records over the considered time period, spanning from multidecadal to centennial scales. Furthermore, these results demonstrate strong associations with the behavior and intensity of the Indian Summer Monsoon, Winter-Westerlies, and the north-south shift of the Intertropical Convergence Zone (ITCZ), thereby contributing to a comprehensive understanding of hydroclimate variations during stalagmite deposition. This technique presents vast opportunities for generating long-term, high-resolution records of hydroclimate and chemical variations by analyzing a relatively large number of samples obtained from diverse geological settings. By judiciously selecting prominent spectral signatures from the LIBS spectrum and employing advanced statistical techniques, essential information regarding the paleoenvironment and hydrology of the cave system can be extracted. This research represents a significant advancement in paleoclimatology, elucidating the intricate interplay between cave hydrology, seasonal amplitude, and the formation of speleothems. Moreover, fs-LIBS technology offers a cost-effective and efficient means of achieving comparable accuracy to reference databases within a shorter timeframe, enhancing its applicability and usefulness in paleoclimatic investigations.