Nanotephra in environmental archives – method development for single-particle multi-element fingerprinting in tephrochronology

Nano-scale volcanic ash particles (nanotephra) are produced during explosive volcanic eruptions. They can travel laterally above the tropopause for thousands of kilometers before returning to Earth’s surface. Within a short time, they will aggregate, settle, and end up in sedimentary sinks, such as lakes and oceans, and might be used as a tephrochronological age marker. These ultra-distal tephra deposits can be highly diluted by geogenic or biogenic background sedimentation. Consequently, the identification of nanotephra in these environmental archives poses an immense analytical challenge. A new generation of time-of-flight mass spectrometers (TOF-MS) can deliver particle specific multi-element information providing the analytical prerequisite to tease out a signal of trace amounts of nanotephra among a majority of background nanoparticles.

Here, we present the first single-particle geochemical data of Eyjafjallajökull nanotephra, Iceland. The sub-micron particles were separated from bulk reference ash collected close to the eruption site and measured in a single-particle inductively coupled plasma TOF-MS. We tested their identification based on trace element heterogeneities in a mixture of tephra and sediment from Millstätter Lake, Austria, serving as a model archive deposition. We are developing this method to identify the source eruption of nanotephra deposited in lake sediment and thereby allow for better dating of the corresponding layer.