2020 | Imprints of volcanic degassing in tree rings
Trees are a great archive as they record environmental changes and impacts at high temporal reso- lution by forming a distinct ring each year. Dendrochronology can be applied to a variety of climato- logical and ecological research questions, including, inter alia, climate reconstructions, fire history, insect outbreaks, and air- and soil pollution. With respect to volcanism, tree-ring studies most com- monly address the climatic fingerprint of large, stratospheric eruptions. The magnitude of volcanic- induced cooling as well as its temporal duration has been estimated based on tree-ring width and density data (e.g., Esper et al., 2013, 2017, Hartl-Meier et al., 2017, Schneider et al., 2017). These approaches are typically applied at larger, continental to hemispheric scales, though interdisciplinary studies of immediate volcanic imprints, in the vicinity of a crater, are potentially equally important. Seiler et al. (2017), for example, outlined that local trees showed distinct growth variations following minor flank eruptions at Mt. Etna. They concluded that tree rings provide valuable information on pre-eruptive volcanic processes, providing the opportunity to reconstruct the processes involved in past volcanic events. Other collaborative studies focused on the accompanying effects of volcanism including CO2 degassing through mofettes. These efforts not only investigated the influence of CO2 enrichment on tree growth, as recorded in the tree-ring width, but also on the ratios of stable carbon isotopes (δ13C) incorporated into the stem wood (e.g., Biondi & Fessenden, 1999, Vodnik et al., 2018, Bogue et al., 2019). Little is, however, known on how trees respond to direct magmatic CO2 emissions and beyond that, any knowledge about the effects of degassing on the chemical compo- sition of wood and the respective signature in tree rings is lacking. Within this interdisciplinary project, we will for the first time measure the chemical features of stem wood of trees growing in the immediate vicinity of mofettes. We intend to focus on the Laacher See and measure the local composition of naturally released soil gases and soil water pH. Using methods of quantitative wood anatomy (von Arx et al., 2016), we will study the detailed growth characteristics of trees near the mofettes, and compare these to trees growing at unaffected sites. We plan to measure the chemical composition of the tree rings using a state-of-the art ITRAX multiscanner at sub-annual resolution. There is a lack of knowledge on how local magmatic degassing affects the uptake of elements by processes in soil and air, and how elements are incorporated into the wood of trees. If our approach in this case study is successful, we can expand this collaborative investigation scheme to other places with volcanic phenomena. This interdisciplinary approach could also be used to reconstruct pre- and post-volcanic degassing over longer periods.
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