Analysis of physical properties and impurities in Greenland ice using optical and Raman microscopy

The aim of this study was to determine relations between the impurity content and the microstructural features of natural ice using Raman spectroscopy. It should be investigated whether certain chemical species can be related to microstructural features, such as grain boundaries. The method of Raman spectroscopy enables to measure the particles in situ without melting the ice samples. Fourteen bags of the NEEM ice core (North Greenland Eemian Ice Drilling), drilled from different depths, were chosen. As a first step, data from fabric analysis (mean grain size and eigenvalue 3) were plotted together with data for the major ions obtained from continuous flow analysis and correlation coefficients between those parameters were calculated. The statistically significant correlations between the chemical and physical parameters remained sporadic. For a case study, two sections from Holocene ice from a depth of 739,75 m to 740,30 m were chosen. After mapping the microstructure of the sections, particles were labelled and counted (from a layer with a focal depth of approximately 500 μm). Using Raman spectroscopy the particles were measured in-situ and the chemical species of most of the compounds could be identified. The major components were sulfate, silica particles, TiO2, some organic species and black carbon, which mostly appeared as a mixed signal. No carbonates were found and no Raman spectra could be obtained from grain boundaries or triple junctions. The particles often appeared to be in clusters or conglomerates. The location of the particles in relation to grain boundaries was difficult to assess due to relaxation of the ice.