Variations in atmospheric sulphate recorded in stalagmites by synchrotron micro-XRF and XANES analyses

We report here the first speleothem time-series of the variability of sulphate, a species whose abundance in catchments is strongly influenced by atmospheric anthropogenic and volcanic sources. Annually-resolved archives of S, Mg, Si and P were generated by applying synchrotron radiation micro X-Ray Fluorescence (XRF) to two speleothems from different sites in northern Italy. X-ray absorption-edge spectrometry proves that the S is in the form of sulphate and XRF mapping demonstrates that S is within calcite and enriched zones are predominantly as layers. A post-1850 A.D. record from the Ernesto cave shows a substantial rise in sulphate, interpreted as reflecting the largely anthropogenically-forced variation of sulphate of the atmospheric boundary layer, moderated by some ecosystem storage. Analysis of the circa 5.2 to circa 5.0 ka interval of a speleothem from Savi cave, where ecosystem retention of S is likely to have been minimal, shows a spiky sulphate record, resembling that of ice cores. A series of sulphate peaks suggest that multiple volcanic sulphate aerosol emissions at that time. This probably enhanced summer temperature cooling thus favouring the preservation of the human mummy of Neolithic-Copper age, the “Iceman” on the watershed between Italy and Austria. Both examples illustrate the power of speleothems to record atmospheric sulphate variability.