High resolution hyperspectral, microphysical and mineralogical interdisciplinary approach applied on the 224 m long ice core drilled on the Adamello glacier (Italian Alps)

The capability of ice-covered surfaces to reflect solar electromagnetic radiation is significantly influenced by mineral dust, one of the primary components of aerosols. This dust alters the reflectance of the ice, causing a larger portion of the radiation to be absorbed, depending on the properties of the dust layer.

The aim of this work is to apply a novel hyperspectral, microphysical and mineralogical interdisciplinary approach for the characterisation of ice cores and the entrapped mineral dust. More than 120 m of the 224 m long ADA270 ice core drilled in 2021 from the Adamello glacier (Pian di Neve, Italian Alps) has been analysed trough this method. A non-destructive Hyperspectral imaging sensor is used to create high-spatial and high-spectral resolution images in the VNIR wavelength range (380-1000 nm).

Hyperspectral measurements were performed at the EuroCold Laboratory of the University Milano-Bicocca (Italy). From these, some optical descriptors such as Albedo, Snow Darkening Index (SDI) and Impurity Index (II) (Di Mauro B. et al, 2015) were extracted. We compared results with independent measurements of dust concentration, grain size (Coulter Counter) and mineralogy (X-Ray Diffraction). Also, single-grain analyses with a Hyperspectral Imaging Microscope Spectrometer (HIMS, Central Washington University, USA) generating reflectance spectra in the same VNIR range were performed in order to explore the possibility to associate the optical footprint of dust layers to specific mineralogical mixtures.

The hyperspectral analysis of the ice core, spanning depths from 3.4 to 124 meters, revealed a sequence of melting-refreezing zones, bubbled regions, and dusty layers, these latter particularly abundant in the upper part of the core. Comparison of the SDI signal with the mineral dust concentrations confirms that, as expected, reflectance diminishes as mineral dust content rises. The mineralogical analyses indicate a notable presence of Quartz, Chlorite, and Biotite, likely due to local transport, along with Kaolinite, a secondary mineral typically linked to Saharan dust transport. By means of the HIMS system various reflectance spectra were extracted from dust samples, providing valuable insights into the optical effects of mineral dust transport through the atmosphere and aiding in the identification of its source region.

By integrating hyperspectral, microphysical, and XRD data, a comprehensive characterization of the inorganic content of the Adamello ice core can be achieved. Micro-hyperspectral measurements offer a qualitative assessment of the optical impact of individual minerals, helping to assess their influence on atmospheric optics, glacier melting rates, and the response of hyperspectral scanning systems.