Colonial mining left its mark in Andean ice cores

by Julia Rosen
Monday, June 1, 2015

When Spanish Conquistadors arrived in the Andes Mountains of Peru and Bolivia, they found a landscape rich in silver. Now, scientists have found evidence of Europe’s voracious demand for the metal hidden in tropical ice cores, which contain a record of colonial mining pollution stretching back to the 1600s.

This history, captured in the chemistry of Peru’s Quelccaya Ice Cap and revealed by Ohio State University researchers and colleagues, unfolds in several steps. Before about 1450, the team found no signs of human activity; the trace metals present in the ice matched those found in natural dust and volcanic ash. After this point, however, the scientists detected a small jump in bismuth concentrations dating to the middle of the 15th century, which they attribute to the production of bismuth bronze by Incan metalworkers.

But the real action started in 1540, soon after Spanish forces toppled the Inca Empire. Here, the ice-core record reveals dramatic increases in many trace metals, including chromium, molybdenum, antimony and lead, which the researchers say reflect intensified colonial mining activities and changes in mining techniques. Specifically, a new method involving mercury would have required the rock to be ground up before processing, potentially producing more airborne dust particles, they wrote in Proceedings of the National Academy of Sciences.

After more than 200 years of Spanish control, the concentration of mining-related elements dropped during the independence wars of the mid-1800s before skyrocketing thanks to the Industrial Revolution.

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