Comparison of co-located ice-core and tree-ring records of atmospheric mercury variability since 1800 CE from the Wind River Range, Wyoming

Abstract:

Anthropogenic activity has resulted in widespread pollution of the potent neurotoxin mercury (Hg). Atmospheric deposition is a major source of Hg deposited to terrestrial ecosystems, and natural archives, including ice cores and lake sediments, have been used to reconstruct atmospheric Hg pollution over past centuries. Recent studies have also developed long-term tree-ring Hg records to examine historical atmospheric Hg variability, as Hg preserved in tree rings has been shown to reflect atmospheric Hg concentrations. The current understanding of Hg uptake pathways and processing within trees, however, is limited and few tree-ring Hg records have been directly evaluated against nearby records from other natural archives. Here we compare co-located ice-core and whitebark pine tree-ring Hg records extending from 1800 to 2018 CE from a remote field site in the Wind River Range, Wyoming, and investigate mechanisms that could potentially explain differences between the Hg records from each archive. Both archives document increasing Hg pollution from anthropogenic activities between 1800 CE and the mid-20^th century followed by decreasing Hg concentrations over recent decades as a result of pollution mitigation efforts, but the precise timing of observed changes in the trees is overall offset earlier relative to the ice core. Results from advection-diffusion model indicate the discrepancies in timing and magnitude between the Hg records is consistent with inward radial movement of Hg across tree rings, but other factors including the form of Hg preserved by each archive and Hg seasonality must also be considered.