Secondary ion mass spectrometry
Speleothem GL-S4 was analysed for S concentration using CAMECA Secondary Ion Mass Spectrometry (SIMS) 1280-HR ion microprobe at the Heidelberg University Ion Probe (HIP) laboratory. The speleothem sample was mounted in resin and polished using 1 μm diamond and coated in 5 nm gold to make the surface conductive and produce negative secondary ions. Samples were sputtered using Cs ions over an analytical spot size of 10 μm including pre-sputtering for 3 minutes to reduce surface contamination. Masses32S and 35Cl were measured using Faraday cups. Count rates were converted into S and Cl concentration using NIST610 standard offering semi-quantified concentrations owing to the different matrix (glass) versus the CaCO3 sample. The concentrations in the NIST610 were 570 ppm for S (Guillong et al. , 2008) and 470 ppm for Cl (Pearce et al. , 1997).