High resolution hyperspectral, microphysical and mineralogical analyses of the ADA270 Adamello ice-core

Ice-covered surfaces of the planet are a pristine glimpse on the climate history of the Earth. Their capability to reflect the solar electromagnetic radiation affects the energy budget through time. Mid-latitude glaciers are highly sensitive to the current atmospheric warming, which is seriously compromising the quality of the signal preserved in the ice. Mineral dust aerosol in the atmosphere can alter the Earth’s energy budget and, when deposited on glaciers surfaces, vary the ice reflectance (REF), so that a major portion of the solar electromagnetic radiation is absorbed as a function of dust concentration, mineralogical composition, particles’ shape, etc. Ice cores from mid-latitude mountain glaciers are essential to infer recent climate variability and anthropogenic impact on a regional scale. The aim of this work is to extract a hyperspectral, microphysical and mineralogical characterisation of the 224 m long ADA270 ice core extracted in 2021 from the Adamello glacier (Pian di Neve, Italian Alps). First, a non-destructive Hyperspectral imaging spectroscopy sensor is used to create highly resolved images described, pixel-by-pixel, by the REF, in the VNIR spectrum (380-1000 nm) with 0.1 cm of spatial resolution and 2-3 nm of spectral resolution (calculated at FWHM). Measurements are done at the EuroCold Laboratory Facilities (University Milano-Bicocca) working at -20 °C. Three optical descriptors are then extracted from REF: Albedo, Snow Darkening Index (SDI) and Impurity Index (II). When REF increases, albedo accordingly increases, while SDI and II decreases. The SDI record is useful to select samples for microphysical and mineralogical analyses, using respectivelly a Beckman Coulter Counter Multisizer in the range 1-30 μm and an X-Ray Diffractometer (XRD) at the Dept. of Earth and Enviromental Sciences (Milano - Bicocca). Finally, an hyperspectral signal calibration will be provided. The hyperspectral characterisation between 3.4-100 m depth of the ice core, highlights a succession of ice lenses, bubbles portions and dusty layers, which respectively show a medium-low SDI-II and medium-high albedo (less than 0.1 − 2.3 ppm) and a high SDI-II and low albedo (more than 3.5 ppm). The XRD shows that the majority of dust layers have a great relative abundance of Quartz, Chlorite and Biotite, in agreement with a local transport from neighboring rock forming minerals. Kaolinite (a secondary mineral) is also largely found and can be attributed to a Saharan dust transport trough the atmosphere. Small percentages of Calcite are sometimes identified. Final results show that Hyperspectral and microphysical data are in agreement. Dusty layers produce a hyperspectral signal useful for microphysical and mineralogical analyses samples selection. Thought XRD data dust source regions can be track back improving the understanding of atmospheric patterns, enhancing the transport simulation models. Unifying hyperspectral, microphysical and XRD data, reference REF curves could work as footprints related to precise mineral groups. Single grain Raman spectroscopy coupled with micro-hyperspectral measurements, will provide a quantitative identification of different minerals encountered in the ice core through time helping identifying their impact on atmospheric optics and glacier melting rate.