engleski

Lead concentrations and stable lead isotopes from a Croatian cave ice profile

Vukušiš Ice Cave (Vukušiš snijeţnica, 44.8N, 14.98E 1490 m asl) is located near the Zaviţan Peak in the northern Velebit Mountains. Thickness of its ice deposit is estimated to be more than 10 m. Lead concentration and stable lead isotopes were analysed on 36 samples of a 2 m long ice core extracted from the ice deposit on 28.10.2008. Pb concentration record is characterized by an overall increasing trend toward the surface. Topmost sample showed the highest Pb concentration, while an interesting secondary maximum emerged between 0.59 and 0.81 m depth. 206Pb/207Pb ratio is characteristically below the expected regional geogenic background (1.202-1.245). Samples from the 1.34-1.49 m depth range, with highly elevated mud content in the ice profile, provided the best agreement (mean 206Pb/207Pb: 1.235) with the expected geogenic background. The rest of the profile showed a slightly decreasing trend towards the surface. The minimum was found in the topmost sample (206Pb/207Pb: 1.069). Ternary plot of 206Pb/207Pb/208Pb shows a gradual shift from a dominantly geogenic composition toward the Broken Hill galena used as antiknock additive in European petrol during the second half of the 20th century. Cave ice record documented an increasing lead contamination being in line with the regional 20th century lead contamination history. Lead isotope ratios provide evidence that increased lead concentrations are due to the increased anthropogenic contribution. The estimated age of the 2 m cave ice core (c. 1950-1980) based on lead concentration and lead isotopes agrees with earlier tritium measurements and the expected lost of most recent accumulation due to negative surface ice mass balance observed in the first decade of the 21th century.

lead; cave ice; cave; Velebit; Croatia

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