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

18O tracer shows diagenetic isotope exchange in biocalcites to be fast, pervasive and species-dependent

Deyanira Cisneros-Lazaro1, Arthur Adams1, Jinming Guo1, Sylvain Bernard2, Lukas P. Baumgartner3, Damien Daval4, Alain Baronnet5, Olivier Grauby5, Torsten Vennemann6, Jarosław Stolarski7, Stéphane Escrig1, and Anders Meibom1,3
Deyanira Cisneros-Lazaro et al.
  • 1Ecole polytechnique fédérale de Lausanne, Environmental Engineering Institute, Laboratory for Biological Geochemistry, Switzerland (
  • 2Museum National d’Histoire Naturelle, Sorbonne Université, France
  • 3Center for Advanced Surface Analysis, Institute of Earth Science, University of Lausanne, Switzerland
  • 4ISTerre, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, France
  • 5CNRS, CINaM, Aix-Marseille Université, France
  • 6Institute of Earth Surface Dynamics, University of Lausanne, Switzerland
  • 7Institute of Paleobiology, Polish Academy of Sciences, Poland

Ocean paleotemperatures have been reconstructed for almost the entirety of the Phanerozoic using the oxygen isotope compositions of calcium carbonates formed by marine organisms and preserved in ocean sediments. However, the isotopic composition of these calcitic tests and shells can be substantially altered through diagenetic processes. Here, we used 18O as an isotopic tracer in controlled experiments designed to simulate early diagenesis of modern benthic foraminifera tests to investigate how fluids penetrate into and exchange oxygen isotopes with these biogenic calcites. Initially pristine tests of Ammonia sp., Haynesina germanica, and Amphistegina lessonii were immersed in an 18O-enriched artificial seawater at 90 °C for hours to days. High-resolution SEM images of the tests before and after the experiments were indistinguishable yet the bulk oxygen isotope compositions of reacted tests revealed rapid and species-dependent isotopic exchange with the water. Correlated SEM, TEM and NanoSIMS imaging of 18O intra-test distributions showed that fluid penetration and exchange is ubiquitous yet heterogenous, and is intimately tied to test ultrastructure and associated organic matter. Species level differences in ultrastructure, quantified through image analysis, explained the observed species-dependent rates of isotopic exchange. Consequently, even calcitic skeletons considered texturally pristine for paleo-climatic reconstruction purposes may have experienced substantial isotopic exchange and hence a critical re-examination of the paleo-temperature record is warranted.

How to cite: Cisneros-Lazaro, D., Adams, A., Guo, J., Bernard, S., Baumgartner, L. P., Daval, D., Baronnet, A., Grauby, O., Vennemann, T., Stolarski, J., Escrig, S., and Meibom, A.: 18O tracer shows diagenetic isotope exchange in biocalcites to be fast, pervasive and species-dependent, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6996,, 2022.