Chart showing mercury stable isotope concentrations in tree rings
Mercury (Hg) stable isotope concentrations in tree rings can be used to differentiate anthropogenic and background contributions to accumulated mercury in tree rings. Positive Δ204Hg and negative Δ200Hg indicate primarily atmospheric source for tree mercury. Here, mass-independent fractionation values for these isotopes across three species in three eras suggests that local industrial sources of atmospheric mercury contributed strongly to tree-ring mercury from 1920-1950. This is indicated by near zero even-mass mass-independent fractionation values for mercury isotopes, indicating shorter atmospheric residence time. Credit: Scanlon et al. [2020], Figure 3
Source: Journal of Geophysical Research: Biogeosciences

The annual growth of trees through photosynthesis is demarcated in seasonal growth rings put on in their stems. Rind width and composition provide clues about the conditions under which that individual grew. These “tree rings” have been used for decades to reconstruct past climates and extreme events. However, there is more to the story.

Scanlon et al. [2020] discover that the concentration of mercury in decadal increments can be used to reconstruct atmospheric mercury in a set of trees in Virginia, USA. Using concentration observations, the researchers found that mercury concentrations in tree rings peaked in the 1930s–1950s while global atmospheric mercury continued to rise. Mercury stable isotopes reveal that this local peak was linked to a local pollution source, most likely from a nearby industrial plant that manufactured the synthetic fabric rayon.

This study is the first attempt to analyze and interpret mercury isotopes in tree rings. The findings open the doors to new analytical approaches to tease out the stories hidden in tree rings about the history of human industrial activity and its impact on the biosphere.

Citation: Scanlon, T. M., Riscassi, A. L., Demers, J. D., Camper, T. D., Lee, T. R., & Druckenbrod, D. L. [2020]. Mercury accumulation in tree rings: Observed trends in quantity and isotopic composition in Shenandoah National Park, Virginia. Journal of Geophysical Research: Biogeosciences, 125, e2019JG005445.

—Ankur Rashmikant Desai, Editor, JGR: Biogeosciences

Text © 2020. The authors. CC BY-NC-ND 3.0
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