Acquisition and analysis of greyscale data from stalagmites using ImageJ software

To reconstruct past climate conditions from speleothems, palaeoclimate researchers utilize a variety of advanced but expensive methods, including various stable isotope ratios and trace element analyses. Greyscale changes can be related to growth and matrix density variations in stalagmites, which in turn are probably dependent on drip rate and dripwater Ca-supersaturation, among other factors. Greyscale analysis is particularly helpful where annual layers are found in stalagmites as the greyscale data can be used to build layer-counting chronologies, similar to varve counting in lacustrine and marine sediments. Greyscale information can further be used as a valuable palaeoclimate proxy. Depending on stalagmite growth rate a spatial resolution of less than five micrometres can be obtained, which might translate to seasonal temporal resolution. Here, we present a low-cost and high-resolution method for acquisition and analysis of greyscale data from speleothems by means of the free ImageJ software. We show how greyscale data can be acquired and visualized and describe how proxy time series can be constructed and proxy record uncertainties estimated using numerical methods. Finally, we provide an example for the application of ImageJ for greyscale analysis on stalagmites. The methodology outlined might be of use to geoscientists working on laminated sediments, and speleothems in particular. © British Cave Research Association 2023.