Impacts of Volcanic Emissions on the Global Biogeochemical Mercury Cycle: Insights From Satellite Observations and Chemical Transport Modeling

Abstract

Volcanism is the largest natural source of mercury (Hg) to the biosphere. However, past Hg emission estimates have varied by three orders of magnitude. Here, we present an updated central estimate and interquartile range (232 Mg a−1; IQR: 170–336 Mg a−1) for modern volcanic Hg emissions based on advances in satellite remote sensing of sulfur dioxide (SO2) and an improved method for considering uncertainty in Hg:SO2 emissions ratios. Atmospheric modeling shows the influence of volcanic Hg on surface atmospheric concentrations in the extratropical Northern Hemisphere is 1.8 times higher than in the Southern Hemisphere. Spatiotemporal variability in volcanic Hg emissions may obscure atmospheric trends forced by anthropogenic emissions at some locations. This should be considered when selecting monitoring sites to inform global regulatory actions. Volcanic emission estimates from this work suggest the pre‐anthropogenic global atmospheric Hg reservoir was 580 Mg, 7‐fold lower than in 2015 (4,000 Mg).

Projecting Global Mercury Emissions and Deposition Under the Shared Socioeconomic Pathways

“…We simulated the time‐dependent fate of future anthropogenic Hg releases separately for each scenario. In each simulation, the model was initialized by calculating the steady state distribution of mercury among reservoirs under a constant geogenic Hg flux of 230 Mg a −1 from subaerial volcanism and 50 Mg a −1 from hydrothermal vents (Geyman et al., 2023). The model was forced with all‐time (2000 BCE to 2010 CE) anthropogenic mercury releases from Streets et al.…”

“…vents (Geyman et al, 2023). The model was forced with all-time (2000 BCE to 2010 CE) anthropogenic mercury releases from Streets et al (2019a) followed by emissions specified in each scenario from 2010 to 2300.…”

“…Mercury (Hg) is a naturally occurring element, but human activities such as mining and fossil‐fuel combustion have released approximately 1.5 Tg of Hg from stable geologic reservoirs to the atmosphere, land, and water over the past 500 years (1510–2010) (Streets et al., 2019a). This has significantly altered the natural biogeochemical Hg cycle (Geyman et al., 2023; Streets et al., 2019a) and adversely affected the health of exposed humans and wildlife (Basu et al., 2023). Reemission of anthropogenic Hg from terrestrial and aquatic ecosystems extends its lifetime in the biosphere (referred to as “legacy Hg”).…”

Assessment of Hg Speciation Changes in the Sedimentary Rock Record From Thermal Desorption Characteristics

“…Geological release processes include natural heating of sedimentary rocks (coal/other hydrocarbon combustion), erosion of Hg‐bearing rocks, and notably via volcanic and hydrothermal activity (Selin, 2009). Among these naturally occurring processes, volcanic Hg emissions are a major component with an estimated flux of 76–700 metric tons yr −1 (Bagnato et al., 2015; Geyman et al., 2023; Pyle & Mather, 2003). Most volcanic mercury emissions are in the form of gaseous elemental mercury, which has an atmospheric residence time of up to 2 years (Lyman et al., 2020), enabling hemispheric or even global distribution (Selin, 2009).…”