EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

New insights from fluorescent organic matter in natural cave systems and active speleothems: a one-year monitoring study from Northwestern Spain

Laura Endres1, Céline Jacquin2, Jacqueline Traber2, Saul Gonzàlez-Lemos3, Laura Rodriquez-Rodriquez3, Jakub Sliwinski4, Nikita Kaushal1, Oliver Kost1, and Heather M. Stoll1
Laura Endres et al.
  • 1Geological Institute, ETH Zürich, Zürich, Switzerland
  • 2EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Überlandstr. 133, CH 8600 Dübendorf, Switzerland
  • 3Departamento de Geología; Universidad de Oviedo, Spain
  • 4School of Earth and Environmental Sciences, University of St. Andrews; Queen’s Terrace, St. Andrews KY16 9TS, United Kingdom

The interpretation of paleoclimate records from speleothems remains a challenging task due to the individual characteristics of each specimen and cave system. Through recent advances in techniques like confocal microscopy and high-resolution geochemical analysis, fluorescent layers in speleothems have become a significant source of information to enhance paleo-seasonal reconstructions, improve age models and, consequently, constrain rates of past climate changes. In this framework, speleothem fluorescence originates from organic matter produced in the soil above the cave, from ancient organic compounds in the bedrock or from microbial processes within the karst. However, the mechanisms leading to the incorporation of fluorescent banding into calcite as well as the properties of transport, storage and decomposition of organic matter in natural karst systems are still under debate. We present results from a one-year monitoring study of fluorescence properties in drip water, sampled from May 2020 to May 2021 in a quasi-monthly resolution at 3-6 locations within the cave system La Vallina in Northwestern Spain. We have measured absorbance spectra and fluorescence exitation-emission matrices; and compare it to drip water geochemistry, fluorescence of active speleothems at the same site and vegetation type above the cave. Our results indicate high gradients of fluorescent properties in drip waters already on a small spatial scale. In the site where active speleothems show fluorescent banding, a humic-like fluorescent signal prevails in cave waters (AC peak, according to Coble nomenclature), while other sites are more likely to be influenced by microbial activity (B/M peak). Humic-like fluorescence is stronger in drip waters during the autumn season, probably due to the increased input by colloids. Yet, simple relationships between the fluorescence in drip water and colloid-associated trace elements like Cu and Y cannot be confirmed. Further, the difference in drip water fluorescence is small compared to the actual intra-seasonal difference retrieved by confocal microscopy in active stalagmites. Therefore, we find drip water composition unlikely to be solely responsible for seasonal enriched fluorescence incorporation in speleothems and favour conceptual models taking moisture-limitation and adsorption into account.

How to cite: Endres, L., Jacquin, C., Traber, J., Gonzàlez-Lemos, S., Rodriquez-Rodriquez, L., Sliwinski, J., Kaushal, N., Kost, O., and Stoll, H. M.: New insights from fluorescent organic matter in natural cave systems and active speleothems: a one-year monitoring study from Northwestern Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8035,, 2022.