We know elements of the story. It was 1911, as Robert Scott and Roald Amundsen raced to the South Pole. Temperatures were below -50˚C. Scott was British; Amundsen a Norwegian. Sled dogs were dying, and the explorers suffered from frostbite. The stakes were high, with financing of future explorations hanging in the balance of which team would be first to reach the South Pole.
But in a sense human impact, if not humans themselves, had beaten both of them to it.
More than 100 years after Amundsen won the race to the South Pole, my research group found that industrial pollution had reached Antarctica more than 20 years before the race to the pole. Thousands of kilometres away, a source of lead, zinc, and silver had been discovered in 1883 at Broken Hill in Australia. Mining and processing operations began soon after, and smelting began at nearby Port Pirie in 1889.
Scott and Amundsen were travelling over apparently untrammelled snow that was in fact heavily contaminated from smelting and mining in Australia, with lead pollution at the time almost as high as at any time since.
Using data from 16 ice cores collected from widely spaced locations in Antarctica, including the South Pole, our team created the most accurate and precise reconstruction to date of lead pollution over Earth’s southernmost continent. This effort required braving temperatures as low as -75˚C with wind chill, as it was at our shallow ice core site about 15km from South Pole. Our new record spans a 410-year period from 1600 to 2010, and is published in the Nature journal, Scientific Reports.
As well as the ice core samples we had taken, our study used data from others sampled by the British Antarctic Survey, the Australian Antarctic Division, and the Alfred Wegener Institute in Germany. These cores from our international collaborations were critical in that they allowed us to examine records from parts of Antarctica rarley visited by US-based scientists, such as the Law Dome region of East Antarctica and a region visited by the Norwegian-United States Scientific Traverse of East Antarctica.
All measurements of lead and other chemicals from this study were made with my collaborators using a unique continuous ice core analytical system that I developed as director of the Desert Research Institute’s ultra-trace ice core analytical laboratory.
Lead is a toxic heavy metal with proven strong potential to harm humans, animals and ecosystems. While the concentrations measured in Antarctic ice cores are very low they record that atmospheric concentrations and the rate of accumulation increased six-fold in the late 1880s – the same time mining began at Broken Hill and smelting at Port Pirie.
The similar timing and magnitude of changes across Antarctica, as well as the characteristic isotopic signature of lead from Broken Hill that was found throughout the continent, suggest that this single source of emissions in southern Australia was responsible for polluting Antarctica at the end of the 19th century, and remains a significant source of pollutants today.
Lead ore is found in deposits containing different isotopes of lead – atoms which contain different numbers of neutrons in the nucleus. This gives different lead deposits mined in different areas a characteristic and recognisable signature, and as lead is found in the atmosphere in generally low background concentrations this makes it an ideal tracer of industrial pollution.
Data from our new set of ice cores show that concentrations of Antarctic lead reached a peak in 1900 and remained high until the late 1920s, with brief declines during the Great Depression and the end of World War II. Then there was a rapid increase in lead concentrations until 1975, remaining high until the 1990s. Lead concentrations have declined across Antarctica since, but are still are about four-fold higher than before industrialisation, despite stricter controls on lead pollutants from industrial sites and the phasing out of leaded transport fuels in many countries.
Our measurements indicate that about 660 tonnes of industrial lead have reached the snow-covered surface of Antarctica during the past 130 years, and clearly detectable pollution continues to accumulate today.