Synchrotron radiation applications to past volcanism archived in speleothems: An overview

Precise dating and correlation of past key volcanic eruptions over a wide geographic area in archives of past climate variability is necessary to support a direct causality between volcanism and climate changes. Research has mostly focused on ice cores and varved sediments, which capture a record of volcanic eruptions in geochemistry and the presence of tephra and criptotephra. Precisely dated cave carbonate deposits, collectively known as speleothems are other valuable palaeoclimate archives, and encode information on past volcanism in their sulphate concentration variability. Due to the physical characteristic of speleothems, detection of sulphate concentration variability requires techniques capable of high spatial resolution, very low limit of detection (ppm to ppb) and low background noise. Synchrotron radiation-based (SR) micro X-ray fluorescence (µXRF) and X-ray absorption near-edge spectrometry prove to be one of the most effective techniques to detect short-lived pulses of sulphate concentration increase, which may be interpreted as being related to atmospheric load due to volcanic eruptions. Here, we provide an overview of existing work as well as a novel interpretation of a SR µXRF-based sulphate series in an annually laminated stalagmite with robust chronology. Sulphate concentration peaks in the years 1815–1816, 1844 and 1947, possibly coinciding with Tambora, Krakatau, and Hekla eruptions. It is concluded that sulphate concentration in speleothems expand the potential to correlate volcanic eruption events at a global scale.