Table 2. Lead and Ba concentrations and Pb isotopic compositions measured in Law Dome ice cores

Lead isotopic compositions and Pb and Ba concentrations have been measured in ice cores from Law Dome, East Antarctica, covering the past 6500 years. 'Natural' background concentrations of Pb (ab. 0.4 pg/g) and Ba (ab. 1.3 pg/g) are observed until 1884 AD, after which increased Pb concentrations and lowered 206Pb/207Pb ratios indicate the influence of anthropogenic Pb. The isotopic composition of 'natural' Pb varies within the range 206Pb/207Pb=1.20-1.25 and 208Pb/207Pb=2.46-2.50, with an average rock and soil dust Pb contribution of 8-12%. A major pollution event is observed at Law Dome between 1884 and 1908 AD, elevating the Pb concentration four-fold and changing 206Pb/207Pb ratios in the ice to ab. 1.12. Based on Pb isotopic systematics and Pb emission statistics, this is attributed to Pb mined at Broken Hill and smelted at Broken Hill and Port Pirie, Australia. Anthropogenic Pb inputs are at their greatest from 1900 to 1910 and from ab. 1960 to ab. 1980. During the 20th century, Ba concentrations are consistently higher than 'natural' levels and are attributed to increased dust production, suggesting the influence of climate change and/or changes in land coverage with vegetation.

已对南极洲东部劳穹（Law Dome）冰芯中的铅同位素组成及铅（Pb）、钡（Ba）浓度进行了测定，该冰芯覆盖过去6500年的时间范围。公元1884年之前，观测到铅（Pb）的‘自然’背景浓度约为0.4皮克/克（pg/g），钡（Ba）约为1.3皮克/克（pg/g）；此后铅浓度升高且206Pb/207Pb比值降低，表明人为源铅的影响。‘自然’铅的同位素组成变化范围为206Pb/207Pb=1.20-1.25、208Pb/207Pb=2.46-2.50，其中岩石和土壤粉尘来源的铅平均贡献率为8%-12%。公元1884年至1908年间，劳穹观测到一次重大污染事件：铅浓度增至四倍，冰芯中206Pb/207Pb比值降至约1.12。基于铅同位素系统学及铅排放统计数据，该污染事件可归因于澳大利亚布罗肯希尔（Broken Hill）开采并在布罗肯希尔与皮里港（Port Pirie）冶炼的铅。人为源铅输入量在1900-1910年及约1960-1980年达到峰值。20世纪期间，钡浓度持续高于‘自然’水平，这归因于粉尘生成量增加，暗示气候变化和/或植被覆盖变化的影响。