A surprising drop in atmospheric mercury levels since the mid-1990s points to a substantial shift in the global biogeochemical cycle of the toxic element.

A team led by Franz Slemr of the Max Planck Institute for Chemistry in Mainz, Germany, compared data from monitoring stations in South Africa, Ireland and Antarctica, as well as measurements taken aboard ships in the Atlantic Ocean. They infer that, globally, mercury levels in the atmosphere have decreased by 20–38% since 1996.

Industrial mercury pollution has remained more or less constant over the past 15 years, leading the authors to suggest that decreasing re-emissions from soils and oceans of mercury deposited before the 1990s is the most likely cause of the downward trend. They add that climate change and ocean acidification may further shift the global mercury cycle.

Atmos. Chem. Phys. 11, 4779–4787 (2011)