Climatic regulation of atmospheric mercury deposition: Evidence from mercury isotopes in an alpine peat core

Abstract Mercury is a global pollutant that can undergo long-range transport in the atmosphere. While anthropogenic activities have largely increased atmospheric Hg emission and deposition since global industrialization, mechanisms governing the atmospheric Hg cycle in preindustrial periods remain unclear. Alpine peatlands receive Hg mainly from atmospheric Hg deposition and are sensitive to climatic changes, therefore alpine peat cores can be a useful archive for understanding the relationship between atmospheric Hg deposition and climate change. Here we reconstruct a 1200-year Hg deposition record based on a core drilled from an ombrotrophic peat bog in Yunnan-Guizhou Plateau, SW China. This core shows a dramatic change of Hg deposition fluxes (30.3–515 μg/m2/yr) associated with variable Hg isotopic composition (δ202Hg: –1.02‰ to –2.01‰; Δ199Hg: –0.16‰ to –0.50‰; Δ200Hg: –0.08‰ to 0.07‰). Using a Δ200Hg-based model, deposition fluxes of atmospheric Hg(0) and Hg(II) were estimated, which vary coherently with climatic indices (e.g., temperature, precipitation, and monsoon intensity). Results of this study imply that atmospheric Hg deposition in SW China is governed by two climate scenarios. In warm-house climates, low precipitation intensity and vegetation growth rates in SW China caused low atmospheric Hg(II) and Hg(0) deposition fluxes, respectively. In cold-house climates, high precipitation intensity and vegetation growth rates caused high atmospheric Hg(II) and Hg(0) deposition fluxes. This study highlights that climate changes can have a strong control on atmospheric Hg deposition.