Mineral dust weathering in the RICE ice core

The RICE ice core was drilled on the NE edge of the Ross Ice Shelf, at the summit of Roosevelt Island (79.364°S, 161.706°W, 550 m a.s.l.), an ice rise 764 m thick, locally-grounded 214 m below sea level (Bertler et al., 2018). The climate record documented in the ice core covers the last 83 ka, providing rich insights on the coastal Antarctic climate. Insoluble impurities in the RICE ice core mainly consist of mineral dust particles. Direct SEM and X-Ray diffraction analyses on single-grains from discrete dust samples extracted from RICE sections show evidence of extensive englacial diagenesis, in particular below ca. 650 m depth. Within the upper part of the core, dust particles are mostly volcanic or aeolian. In the deepest part of the core, conversely, aeolian dust particles show authigenic, eudral crystals grown on their surface. Also, individual crystals not showing signs of atmospheric transport both possibly resulting from in situ mineralization have been observed. Mineral neoformation likely results from the interaction between dust and fluids concentrating in ice crystal boundaries and triple junctions. Newly-formed minerals include Fe-bearing compounds such as Jarosite, Goethite, Magnetite and Hematite. These results are in line with the ice-weathering model proposed for ice deeper than about 1500 meters at Talos Dome (Baccolo et al., 2021a, 2021b), although in the case of RICE the depth of englacial mineralization is much shallower. Our results corroborate the finding that weathering and englacial diagenesis is a common process at depth inside thick ice sheet, potentially affecting the climatic interpretation of dust records in deep ice cores. Considering the different depth at which such processes have been found in RICE and Talos Dome ice cores, it remains to be understood which are the limiting factors controlling the initiation of such englacial reactions.

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Baccolo, G., Delmonte, B., Niles, P.B., ... Snead, C., Frezzotti, M. Jarosite formation in deep Antarctic ice provides a window into acidic, water-limited weathering on Mars, Nature Communications, 2021, 12(1), 436

Baccolo, G., Delmonte, B., Di Stefano, E., ... Marcelli, A., Maggi, V. Deep ice as a geochemical reactor: Insights from iron speciation and mineralogy of dust in the Talos Dome ice core (East Antarctica), Cryosphere, 2021, 15(10), pp. 4807–4822