ALBERT

Description: Impurities in polar ice do not only allow the re- construction of past atmospheric aerosol concentrations but also influence the physical properties of the ice. However, the localisation of impurities inside the microstructure is still un- der debate and little is known about the mineralogy of solid inclusions. In particular, the general mineralogical diversity throughout an ice core and the specific distribution inside the microstructure is poorly investigated; the impact of the mineralogy on the localisation of inclusions and other pro- cesses is thus hardly known. We use dust particle concen- tration, optical microscopy, and cryo-Raman spectroscopy to systematically locate and analyse the mineralogy of micro- inclusions in situ inside 11 solid ice samples from the up- per 1340 m of the East Greenland Ice Core Project ice core. Micro-inclusions are more variable in mineralogy than pre- viously observed and are mainly composed of mineral dust (quartz, mica, and feldspar) and sulfates (mainly gypsum). Inclusions of the same composition tend to cluster, but clus- tering frequency and mineralogy changes with depth. A va- riety of sulfates dominate the upper 900 m, while gypsum is the only sulfate in deeper samples, which however contain more mineral dust, nitrates, and dolomite. The analysed part of the core can thus be divided into two depth regimes of different mineralogy, and to a lesser degree of spatial distri- bution, which could originate from different chemical reac- tions in the ice or large-scale changes in ice cover in north- east Greenland during the mid-Holocene. The complexity of impurity mineralogy on the metre scale and centimetre scale in polar ice is still underestimated, and new methodological approaches are necessary to establish a comprehensive un- derstanding of the role of impurities. Our results show that applying new methods to the mineralogy in ice cores and recognising its complexity, as well as the importance for lo- calisation studies, open new avenues for understanding the role of impurities in ice cores.