Andy Baker

It was April 2021, and myself and Pauline Treble (ANSTO) had emails about a forthcoming online XFM and IRM microscopy workshop at the Australian Synchrotron. That’s x-ray fluorescence mapping and infra-red mapping at very high spatial and optical resolution. We already used XFM to map elements in stalagmites, but what about using IRM to map organic matter?

One workshop later and after an e-mail to the only people that I knew that had tried this before (Silvia Frisia and Andrea Borsato at the University of Newcastle), myself, Pauline and Micheline Campbell were in contact with the facility about the feasibility of mapping organic matter in stalagmites using infra-red energy. We got the thumbs up for submitting a beamline proposal, Liza McDonough (ANSTO) led that, and by the end of 2021 we had beamtime approved for Easter 2022.

Roll on almost three years, a further application for beamtime and some very long overnight experiments with long shifts from the team (and especially Liza and Micha). I can still recall the whirring and tap tap tap of the micro-ATR on calcite. Liza has published the results of our experiments in the journal Organic Geochemistry, which you can access here (Open Access).

The paper includes a wide range of data and methods. If you are interested in the use of non-destructive, high-resolution ATR (attenuated total reflectance) infra-red mapping of stalagmite calcite or other carbonates, it might be for you. For anyone interested in the IR spectra asssociated with wildfires, we include end-member spectra of soils, vegetation, wildfire ash, and calcite and aragonite. And we have maps of organic matter in stalagmites that have sub-annual resolution on stalagmite material that grew when wildfires passed over the land surface and the soluble ash fraction was transported by drip water to the cave.

This work was funded through the Australian Research Council Discovery Project DP200100203. We acknowledge the support of ANSTO in providing access to instruments, capabilities and facilities used in this study via portal access proposals 17905 and 18777.