Early atmospheric contamination on the top of the Himalayas since the onset of the European Industrial Revolution

Significance

Since the beginning of the European Industrial Revolution (∼1780 AD), increases in the deposition of atmospheric toxic metals were recorded in an ice core extracted from the Dasuopu glacier, at very high elevation (7,200 m) in the Himalayas. Initially, these contaminants were transported by the winter westerlies as combustion products of coal, likely used in Europe, during the 19th century, with the possible contribution from the emissions of large-scale fires used for deforestation. During the 20th century, unexpected low levels of toxic metals suggest that multidecadal changes in atmospheric circulation are the most important factor to explain the impact of human emissions on the chemistry of the troposphere in the Himalayas at this time.

Abstract

Because few ice core records from the Himalayas exist, understanding of the onset and timing of the human impact on the atmosphere of the “roof of the world” remains poorly constrained. We report a continuous 500-y trace metal ice core record from the Dasuopu glacier (7,200 m, central Himalayas), the highest drilling site on Earth. We show that an early contamination from toxic trace metals, particularly Cd, Cr, Mo, Ni, Sb, and Zn, emerged at high elevation in the Himalayas at the onset of the European Industrial Revolution (∼1780 AD). This was amplified by the intensification of the snow accumulation (+50% at Dasuopu) likely linked to the meridional displacement of the winter westerlies from 1810 until 1880 AD. During this period, the flux and crustal enrichment factors of the toxic trace metals were augmented by factors of 2 to 4 and 2 to 6, respectively. We suggest this contamination was the consequence of the long-range transport and wet deposition of fly ash from the combustion of coal (likely from Western Europe where it was almost entirely produced and used during the 19th century) with a possible contribution from the synchronous increase in biomass burning emissions from deforestation in the Northern Hemisphere. The snow accumulation decreased and dry winters were reestablished in Dasuopu after 1880 AD when lower than expected toxic metal levels were recorded. This indicates that contamination on the top of the Himalayas depended primarily on multidecadal changes in atmospheric circulation and secondarily on variations in emission sources during the last 200 y.