High-resolution XRF-CS/ICP-MS mineral element data calibration and potential applications in sub-Antarctic peat records

Abstract

Abstract Peatlands are important environmental archives and mineral dust trapped in peat cores from multiple sites can be used to track past changes in hemispheric and global wind circulation patterns. X-ray Fluorescence Core Scanning (XRF-CS) can rapidly geochemically characterise minerals deposited in peat at sub-millimetre-resolution, but calibration is needed to obtain quantitative data. Here, we present a unique calibration of > 14,000 contiguous mm-scale XRF-CS measurements depth-matched to 268 interval-based cm-scale Inductively Coupled Plasma Mass Spectrometry (ICP-MS) quantitative measurements from five peat records located on the west coasts of four sub-Antarctic islands impacted by the Southern Hemisphere Westerly Winds. Of eight calibration models tested, a four-element (Ca, Ti, Sr, Zr) multivariate partial least squares (PLS) model optimised for the widely used dust flux elements Ti and Zr accounts for covariance and provides the most reliable predicted XRF-CS concentrations for Ti (R 2 CV  = 0.76, RMSEP boot = 2203 ± 705 mg kg − 1 , R 2 pred . = 0.87, RMSE pred . = 2136 mg kg − 1 , P  < 0.0001). Predictions for Zr are indicative due to low Zr concentrations, but calibrated Ti and Zr XRF-CS concentrations align well with ICP-MS Ti and Zr concentrations for all five peatland sites. Our multivariate calibration protocol expands the scope of quantitative high-resolution palaeoenvironmental and geochemical research potentially to decadal–centennial timescales for peat records from, and beyond, the sub-Antarctic islands.