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

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.

Keywords: North Atlantic Oscillation; ice cores; monsoon; paleoenvironment; trace metals.

Fig. 1.

Location and study site. The Dasuopu ice core drilling site in the Himalayas (marked by a star) and other significant locations mentioned in the text are shown. Map courtesy of Wikimedia Commons/NASA.

Fig. 2.

Climatic and geochemical parameters in the Dasuopu ice core, all shown as decadal medians. From the Top: (A) snow accumulation and deuterium excess (35); (B) dust particle and sulfate concentrations (35, 38); (C) Al concentration (gray dots represent singles sample values; cityscape curves depict decadal median [in bold] bracketed by median absolute deviation); (D and E) Al, As fluxes and crustal EFs. The vertical dotted lines outline the 1810 to 1880 AD period with high snow accumulation.

Fig. 3.

Chemical fluxes and crustal EFs (decadal medians) of Cd, Cr, Mo, Ni, Sb, and Zn that show the largest variations in the Dasuopu ice core during the last 500 y. The vertical dotted lines outline the 1810 to 1880 AD period with high snow accumulation, while the gray band spans the period of anthropogenic contributions.

Fig. 4.

Hydroclimatology, anthropic factor, biomass burning, and coal production. The annual records, overlain by 5-y median smoothing, of the following: (A) monsoon summer (June to September [JJAS]) precipitation in India (46), (B) November to December North Atlantic Oscillation Index (NAO) (42), and (C) Dasuopu snow accumulation (35). (D) Decadal median of the anthropic factor 1 (Zn, Mo, Cd, Sb) from positive matrix factorization (PMF) of the trace metal concentration dataset of the Dasuopu ice core and (E) charcoal influx z score in the globe and in the Northern Hemisphere (14). (F) Cumulative global and regional coal production since 1800 AD (9). The vertical dotted lines outline the 1810 to 1880 AD period with high snow accumulation, while the gray band spans the period of anthropogenic contributions to trace metal deposition in Dasuopu.