Development and application of new methods to perform iron speciation in ice cores

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 and finally into sulphate. Its discrete and continuous quantification is currently used to determine the ice layers impacted by volcanic emissions. However, these methods struggle to achieve the sensitivity and the limits of detection needed for deep polar ice analyses. Volcanoes emit a wide variety of other chemical compounds, including large quantities of soluble and bioavailable iron which, especially at the low pH values of the volcanic aerosol, is present as Fe2+. Here, we present a new high-resolution method for the continuous determination of Fe2+ species in ice cores. 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.