The Himalayan cryosphere, often described as the water tower of Asia, supplies meltwater to billions of people downstream. But the same snowfields and glaciers that store this water also capture atmospheric deposition with remarkable efficiency. Snow scavenging, the process by which falling and lying snow removes aerosol particles and dissolved gases from the air, makes high-altitude snowpacks sensitive recorders of both natural mineral dust and anthropogenic emissions. The review collates studies from the Western, Central and Eastern Himalayas as well as the Tibetan Plateau, sometimes called the Third Pole, and reveals a chemical signature that is anything but pristine.

One of the clearest findings across the compiled datasets is the overwhelming dominance of crustal ions, particularly calcium (Ca2+) and bicarbonate (HCO3−). These species originate largely from the weathering of mineral dust, which is lifted from arid regions of Central and South Asia and deposited onto mountain snowfields. However, the review also documents notable enrichment of trace elements such as zinc (Zn), lead (Pb) and manganese (Mn), which cannot be explained by crustal sources alone. The combination points to a dual influence: natural geological weathering working alongside emissions from industry, fossil fuel combustion and biomass burning transported over long distances.

Spatial patterns emerging from the review are striking. Pollutant concentrations are consistently higher on the southern slopes of the Himalayas than on the northern side. This asymmetry reflects the geography of emission sources. The southern slopes face the densely populated Indo-Gangetic Plain, where industrial activity, vehicular traffic and agricultural burning generate vast quantities of aerosols and heavy metals. The northern slopes, facing the more sparsely populated Tibetan Plateau, receive comparatively less direct pollution, although long-range transport still delivers contaminants from Central Asia and beyond.

Seasonal variability adds another layer of complexity. The review indicates that accumulation of pollutants in snow is enhanced during non-monsoon periods, when dry conditions and reduced precipitation allow contaminants to build up in the snowpack without being flushed away. During the Indian summer monsoon, heavy rainfall and snowfall act as efficient scavenging agents, removing large amounts of material from the atmosphere but also depositing it onto the cryosphere in concentrated pulses. The interplay between monsoon dynamics and western disturbances, weather systems that bring moisture from the Mediterranean and Atlantic regions, plays a key role in transporting contaminants from South and Central Asia into the high mountains.

The implications of this contamination extend beyond the chemistry of the snow itself. Trace elements such as lead, mercury and cadmium are toxic even at low concentrations, and their presence in glacier snow raises concerns about what happens when that snow melts. Meltwater carries dissolved and particulate contaminants into downstream rivers, potentially affecting drinking water quality, aquatic ecosystems and agricultural soils. Studies cited in the review, including work on the Rongbuk Glacier on Mount Everest and the Zhadang Glacier on the southern Tibetan Plateau, have documented mercury export in glacier runoff, highlighting a direct pathway from atmospheric deposition to human exposure.

Black carbon and light-absorbing particles further complicate the picture. Although the review focuses primarily on ionic species and trace elements, it draws on related research showing that dark particles deposited on snow surfaces reduce albedo, the reflectivity of the snow, causing it to absorb more solar radiation and melt faster. This accelerates glacier retreat across the region, which has been documented extensively from the Dokriani Glacier in Garhwal to the Machoi Glacier in Kashmir and the glaciers of Sikkim. The combination of chemical contamination and physical darkening creates a feedback loop in which pollution both records and drives cryospheric change.

Melt-induced fractionation presents another technical challenge for interpreting the archive. As snowpacks warm and melt, ions and trace elements are not lost uniformly. Some species are eluted preferentially in the first meltwater fractions, while others remain concentrated in the remaining snow. This means that the chemical record preserved in a snowpit or ice core may not perfectly reflect the original atmospheric deposition. The review acknowledges this complication, drawing on studies from the Alps and other mountain regions that have quantified how meltwater redistributes solutes within the snowpack, and notes that such processes must be accounted for when reconstructing past atmospheric conditions from glacial archives.

Despite the growing body of research, the review identifies critical data gaps, particularly in the Eastern Himalayas. While the Western Himalayas, the Central Himalayas and the Tibetan Plateau have been relatively well studied, the Eastern Himalayan region, spanning parts of Arunachal Pradesh, Sikkim, Bhutan and northeastern India, remains underrepresented in the published record. This gap is significant because the Eastern Himalayas receive different atmospheric circulation patterns and may experience distinct pollution transport pathways. Without standardised monitoring across all sub-regions, it is difficult to build a complete picture of contaminant fluxes into the cryosphere or to predict how these will change under future emission scenarios and a warming climate.

The authors emphasise the need for expanded and standardised monitoring programmes to better assess future ecological and health risks associated with cryospheric contamination. As the climate warms and glaciers retreat, the pollutants stored in snow and ice will be released into meltwater over increasingly short timescales. Understanding the full inventory of contaminants locked in the Himalayan cryosphere, and the mechanisms by which they arrived there, is therefore not merely an academic exercise. It is a prerequisite for protecting the water security and public health of the more than a billion people who depend on the rivers born from these mountains. The review serves as both a synthesis of two decades of research and a call to action for the scientific community to fill the remaining gaps before the archive itself disappears.

Subject of Research: Major ionic species and trace element contamination in Himalayan snow and glacier ice

Article Title: A review of major ionic species and trace elements in the Himalayan cryosphere

Article References: Sharma, K. D., Dutta, J., & Jyethi, D. S. (2026). A review of major ionic species and trace elements in the Himalayan cryosphere. Environmental Monitoring and Assessment, 198(9), Article 991. https://doi.org/10.1007/s10661-026-15840-x

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15840-x

Keywords: Himalayas, cryosphere, snow chemistry, trace elements, major ions, glacier meltwater, atmospheric deposition, Tibetan Plateau, black carbon, heavy metals, monsoon, pollution transport