Fe²⁺ in ice cores as a new potential proxy to detect past volcanic eruptions

Volcanic eruptions are widely used in ice core science to date or synchronize ice cores. Volcanoes emit large amounts of SO₂ that is subsequently converted in the atmosphere into sulfuric acid/sulphate. Its discrete and continuous quantification is currently used to determine the ice layers impacted by volcanic emissions, but available high-resolution sulphate quantification methods in ice core (Continuous Flow Analysis (CFA)) struggle with insufficient sensitivity. Here, we present a new high-resolution CFA chemiluminescence method for the continuous determination of Fe²⁺ species in ice cores that shows clear Fe²⁺ peaks concurrent with volcanic sulphate peaks in the ice core record. The method, applied on a Greenland ice core, correctly identifies all volcanic eruptions from between 1588 to 1611 and from 1777 to 1850. The method has a detection limit of ∽5 pg g^-1 and a quadratic polynomial calibration range of up to at least 1760 pg g^-1. Our results show that Fe²⁺ is a suitable proxy for identifying past volcanic events.