Modern and Fossil Foliar Mercury Concentrations Reflecting Atmospheric Mercury Levels

Gas emissions during large-scale volcanism, which are comparable in volume (and possibly flux) to modern anthropogenic emissions, significantly affected the composition of Earth’s atmosphere, not only by increasing atmospheric pCO2 but also by enhancing the concentrations of gaseous or aerosol-bound toxic metals, like mercury (Hg). Present-day environmental pathways of mercury are highly monitored; however, environmental Hg fluxes and atmospheric concentrations are largely unconstrained both for the pre-industrial and geological past. As terrestrial flora acts as an intermediate sink in the natural mercury cycle, and deciduous leaves predominantly acquire their Hg concentration through direct atmospheric uptake, we propose a new approach to reconstructing changes in atmospheric Hg concentrations by analysing Hg levels in modern and fossil leaf tissue. The natural variability of Hg concentrations in modern Gingko biloba leaves was determined from multiple geographic localities characterized by different atmospheric Hg levels. Subsequent analyses of the Hg concentration in fossil leaf-cuticle from the Triassic–Jurassic mass extinction event (~201 Ma), as recorded in the Astartekløft (Greenland) sedimentary succession of East Greenland, and which has a temporal correlation to volcanic activity associated with the emplacement of the Central Atlantic Magmatic Province (CAMP), show significantly higher plant Hg concentrations than observed within modern natural variability. This suggests that fossil plant tissue may trace elevated atmospheric Hg levels at that time and may be used to examine Hg variations in past atmospheres to detect the timing and environmental signature of past volcanic events.