Continuous Characterization of Insoluble Particles in Ice Cores Using the Single-Particle Extinction and Scattering Method.

This study presents the integration of the single-particle extinction and scattering (SPES) method in a continuous flow analysis (CFA) setup. Continuous measurements with the instrument allow for the characterization of water-insoluble particles in ice cores at high resolution with a minimized risk of contamination. The SPES method can be used to investigate particles smaller than 1 mu m, which previously could not be detected by instruments typically used in CFA. Moreover, the SPES method provides not only the particle concentration and size distribution but also the effective refractive index. We show that nonabsorbing mineral particles and absorbing particles from both wildfires and fossil fuel burning can be detected with the SPES method in shallow ice cores from North-East Greenland. The concentration record retrieved with SPES correlates well with established methods used in continuous measurements of dust content in ice cores. Year-to-year variations in the number distribution of the diameter are only detectable by stacking annual layers because of the low nonabsorbing particle concentration of late Holocene ice of approximately 6 x 104 mL-1. The median diameter in the bottom 20 m of the EGRIP-S7 core is found to be 0.75 mu m (0.72 mu m) during the annual maximum (minimum) in dust concentration.