Mercury Deposition in South China Across the Ordovician-Silurian Transition: Implications for Climate Change

Most of the global climate changes are closely associated with volcanic activity. However, the link between global cooling during the Ordovician-Silurian (O-S) transition and volcanism remains unclear due to limited constraints on large volcanic events before, during, and after the peak of the Hirnantian glaciation (PHG). Here, we present high-resolution mercury (Hg) concentrations and isotopes from South China across the O-S transition to assess volcanic activity and its contributions to climate changes. Anomalous Hg enrichments and volcanic-range Hg isotopes in samples above volcanic ash layers confirm the effectiveness of Hg as a tracer of volcanic events. Variations in Hg isotopes across the O-S transition reveal multiple Hg sources related to volcanic activity, that is, dominant volcanic Hg input during pre-PHG and post-PHG-2, deposition of volcanic-sourced atmospheric Hg(II) to seawater during PHG, and increased terrestrial Hg input from enhanced weathering during post-PHG-1. We propose that prolonged global cooling was driven by an albedo catastrophe caused by volcanic aerosols and sustained by reduced atmospheric CO₂ levels due to enhanced organic carbon burial and weathering. This study highlights Hg as a tracer of volcanic activity and provides new evidence on the role of volcanism in driving climate changes across the O-S transition.