Climate and plant traits drive a cross-continental imbalance in atmospheric Hg uptake.

Abstract

Tropical rainforests, particularly the Amazon, function as the Earth's lungs yet absorb mercury (Hg) emitted worldwide. By introducing climate-driven variations in foliar functional traits into a global model of forest Hg uptake, we uncovered an inter-continental spatial decoupling between Hg sources and sinks. Unexpectedly, the minimally industrialized rainforests of South America and Africa exhibit the world's highest atmospheric Hg accumulation rates and greatest biomass, thus disproportionately sequestering Hg released from industrialized regions. This imbalance arises from climate-specific leaf traits that enhance Hg fixation towards lower latitudes. The model constrains global forest Hg uptake to 1155 ± 422 Mg yr^-1, sharply reducing prior uncertainties (320-3138 Mg yr^-1) and nearly equilibrating with global litterfall deposition (1180 ± 710 Mg yr^-1). These findings urge a re-assessment of the Minamata Convention's effectiveness and highlight the vulnerability of tropical forests to anthropogenic Hg inputs and to climate-induced shifts in vegetation and terrestrial Hg reservoirs.