Chuxian LI, Jeroen Sonke , Gael Le Roux, Natalia Piotrowska, Nathalie Van der Putten, Stephen J Roberts, Tom Daley, Emma Rice, Roland Gehrels, Maxime Enrico

Remote northern (NH) and southern hemisphere (SH) lake sediment and peat records of mercury (Hg) deposition show a ×3 to ×5 Hg enrichment since pre-industrial times (<1880AD), leading to the common perception that global atmospheric Hg enrichment is moderate and uniform. Anthropogenic Hg emission in the NH is, however, approximately four times higher than in the SH. Here we reconstruct atmospheric Hg deposition to four remote SH peatlands and review sediment and peat Hg records from both hemispheres. We observe a ×4 enrichment in SH Hg deposition from pre-anthropogenic (<1450AD) to late 20th century periods, which is lower than the large ×16 all-time enrichment in NH Hg deposition. We attribute this difference to lower anthropogenic Hg emissions in the SH, and higher natural atmospheric SH Hg concentrations, supported by ×2 higher natural background Hg accumulation in SH peat records. We suggest that the higher SH natural Hg concentrations reflect the SH land-ocean distribution, with higher marine SH Hg emissions driven by transport of NH Hg to the SH by the Ocean conveyor belt. Our findings suggest that Hg background levels and anthropogenic enrichment in both hemispheres are different and must be taken into account in international Hg assessments and environmental policy.