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Impact of Po Valley emissions on the highest glacier of the Eastern European Alps

by J. Gabrieli, L. Carturan, P. Gabrielli, N. Kehrwald, C. Turetta, G. Cozzi, A. Spolaor, R. Dinale, H. Staffler, R. Seppi, G. dalla Fontana, L. Thompson, C. Barbante show all authors
Atmospheric Chemistry and Physics ()

Abstract

In June 2009, we conducted the first extensive glaciological survey of\nAlto dell'Ortles, the uppermost glacier of Mt. Ortles (3905 m a.s.l.),\nthe highest summit of the Eastern European Alps. This section of the\nAlps is located in a rain shadow and is characterized by the lowest\nprecipitation rate in the entire Alpine arc. Mt. Ortles offers a unique\nopportunity to test deposition mechanisms of chemical species that until\nnow were studied only in the climatically-different western sector. We\nanalyzed snow samples collected on Alto dell'Ortles from a 4.5 m\nsnow-pit at 3830 m a.s.l., and we determined a large suite of trace\nelements and ionic compounds that comprise the atmospheric deposition\nover the past two years.\nTrace element concentrations measured in snow samples are extremely low\nwith mean concentrations at pg g(-1) levels. Only Al and Fe present\nmedian values of 1.8 and 3.3 ng g-1, with maximum concentrations of 21\nand 25 ng g-1. The median crustal enrichment factor (EFc) values for Be,\nRb, Sr, Ba, U, Li, Al, Ca, Cr, Mn, Fe, Co, Ga and V are lower than 10\nsuggesting that these elements originated mainly from soil and mineral\naerosol. EFc higher than 100 are reported for Zn (118), Ag (135), Bi\n(185), Sb (401) and Cd (514), demonstrating the predominance of\nnon-crustal depositions and suggesting an anthropogenic origin.\nOur data show that the physical stratigraphy and the chemical signals of\nseveral species were well preserved in the uppermost snow of the Alto\ndell'Ortles glacier. A clear seasonality emerges from the data as the\nsummer snow is more affected by anthropogenic and marine contributions\nwhile the winter aerosol flux is dominated by crustal sources. For trace\nelements, the largest mean EFc seasonal variations are displayed by V\n(with a factor of 3.8), Sb (3.3), Cu (3.3), Pb (2.9), Bi (2.8), Cd\n(2.1), Zn (1.9), Ni (1.8), Ag (1.8), As (1.7) and Co (1.6).\nWhen trace species ratios in local and Po Valley emissions are compared\nwith those in Alto dell'Ortles snow, the deposition on Mt. Ortles is\nclearly linked with Po Valley summer emissions. Despite climatic\ndifferences between the Eastern and Western Alps, trace element ratios\nfrom Alto dell'Ortles are comparable with those obtained from\nhigh-altitude glaciers in the Western Alps, suggesting similar sources\nand transport processes at seasonal time scales in these two distinct\nareas. In particular, the large changes in trace element concentrations\nboth in the Eastern and Western Alps appear to be more related to the\nregional vertical structure of the troposphere rather than the synoptic\nweather patterns.

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