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

Ice-covered surfaces capability to reflect the solar electromagnetic radiation is very important for can be affected by mineral dust (one of the main components of aerosols), that vary the ice reflectance so that a major portion of the radiation is absorbed as a function of dust layer properties. 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 spectral resolution images characterized, pixel-by-pixel, by a reflectance curve in the VNIR wavelength range (380-1000 nm). Measurements are done at the EuroCold Lab. (University Milano-Bicocca). Three optical descriptors are extracted from reflectance: Albedo, Snow Darkening Index (SDI) and Impurity Index (II). When the reflectance increases, albedo accordingly increases, while SDI and II decreases. Albedo and SDI records are useful to select samples for microphysical and mineralogical analyses, identifying peaks respectively for melting-refreezing regions and bubbled portions (high and medium/high albedo) and mineral dust layers (medium/high and high SDI). A Beckman Coulter Counter Multisizer 4E is used for microphysics with a 50 µm capillary (1-30 µm) and an X-Ray Diffractometer (XRD) for mineralogy, at the Dept. of Earth and Environmental Sciences (University Milano - Bicocca). Finally, a hyperspectral microscope (HIMS) will produce reflectance spectra in the same VNIR range of single dust grains (Central Washington University), in order to associate an optical footprint to mineral grains. The hyperspectral characterisation between 3.4-124 m depth of the ice core, highlights a succession of various melting-refreezing regions, bubbled portions and dusty layers that are more abundant in the less deep sections of the core. Comparing the SDI signal with the high concentrated mineral dust portions, has been observed that as expected the reflectance decreases when the mineral dust content increases. The XRD shows a great relative abundance of Quartz, Chlorite and Biotite, for local transport and Kaolinite (a secondary mineral), that can be attributed to a Saharan dust transport. With the HIMS (Central Washington University, WA), various reflectance spectra have been extracted for dust samples. This could also help to understand better the optical impact of such mineral dust transport trough the atmosphere and track back the source region. Unifying hyperspectral, microphysical and XRD data, a complete characterisation of ice-cores inorganic content can be done. Micro-hyperspectral measurements, provide a qualitative evaluation of different single minerals optical impact, helping identifying their impact on atmospheric optics, glacier melting rate and the hyperspectral scanning system signal.