Tracing volcanic events in tree rings

Understanding the impact of volcanic eruptions on climate over the last two millennia is essential to place current anthropogenic climate change into a long-term context. High-resolution proxy archives are crucial for this purpose, yet their availability decreases rapidly back in time. Besides ice cores, speleothems and corals, tree rings represent a uniquely valuable archive, providing records with annual resolution of past-climate change. Volcanic eruptions are among the most impactful natural forcings on Earth’s climate, through the injection of gaseous plumes into the atmosphere that can induce warming or cooling of the planet surface. While some of these impacts are well-known and studied, there are many older volcanic events whose details are unknown or uncertain, due to the lack of direct historical evidence.Volcanic plumes transport volatile elements (e.g., S, Fe, Zn, Cu, Hg) that can be absorbed by trees and recorded in the yearly tree-ring layers. So far, dendrochemistry has been widely applied to assess anthropogenic pollution, but our research explores its potential as a novel proxy: by identifying chemical spikes of these elements in tree rings of known age, it may be possible to correlate them with known volcanic eruptions or identify previously unrecognized volcanic events. Here we present data obtained at Diamond synchrotron on tree rings from juniper (Juniperus communis) samples from Kevo, Finland, whose dendrochronological records extend back to the early Middle Ages. These measurements revealed distinct peaks in metal elements such as Zn and Cu, which are typically enriched in volcanic plumes and can be hosted in the wood as semi-nutrients. Some concentration peaks detected in the tree rings correspond to the ages of major Icelandic eruption from the lower Middle Ages.These preliminary results suggest that dendrochemical analyses may provide a new archive of past volcanic activity. If validated, this approach could significantly improve reconstructions of volcanic eruptions of the past and corresponding climate variability over the last two millennia.