Seasonal variability in the input of lead, barium and indium to Law Dome, Antarctica

Lead (Pb) isotopic compositions and concentrations, and barium (Ba) and indium (In) concentrations have been determined at monthly resolution in five Law Dome (coastal Eastern Antarctica) ice core sections dated from ~1757 AD to ~1898 AD. 'Natural' background Pb concentrations in ~1757 AD average ~0.2 pg g -1 and can be attributed to mineral dust and volcanic emissions, with 206Pb/207Pb ratios reaching up to 1.266 +- 0.002. From ~1887 AD to ~1898 AD, Pb concentrations reached ~5 pg g -1 and 206Pb/207Pb ratios decreased to 1.058 +- 0.001 as a result of additional inputs of Pb from anthropogenic sources. Seasonal variability in the late 1880s has been investigated by decoupling volcanic Pb from the total measured Pb concentrations, revealing spring and autumn maxima, and consistent winter minima, in anthropogenic Pb and mineral dust (Ba) concentrations. We link this variability to the annual cycle in the position and strength of the Antarctic Circumpolar Trough and, the Southern Ocean westerly winds to the north of the trough region. During the autumn and spring seasons, these systems increase in strength, transporting more impurity laden air from the Southern Hemisphere continental regions to Eastern Antarctica and Law Dome. As this Pb is isotopically identical to that emitted from south-eastern Australia (Broken Hill, Port Pirie) this implies a relatively direct air trajectory pathway from southern Australia to Law Dome (Eastern Antarctica).