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

The research team collected 148 water samples from 19 glacier-fed rivers across central Svalbard, spanning a wide variety of rock types and ice conditions. Every single river they tested contained more methane than would be expected from ordinary contact with the atmosphere. The most methane-rich waters reached concentrations up to 425 times atmospheric equilibrium levels, a striking signal that something beneath the ice is supplying the gas in abundance. Co-author Silje Waaler explained that the survey was deliberately designed to capture the diversity of glaciers across the region, giving the team a clearer picture of why some glacier rivers carry far more methane than others.

One of the study’s most important conclusions concerns the origin of the methane. In Greenland, scientists have previously documented microbes producing methane beneath the ice. On Svalbard, however, the methane appears to be geological rather than biological. Much of the archipelago is underlain by old shale layers rich in organic carbon. Over millions of years, heat and pressure have transformed that buried organic material into methane and other gases, creating a vast reservoir of ancient carbon locked in the bedrock. When meltwater reaches these rocks, it can pick up the gas and carry it away.

To confirm the methane’s source, the researchers analysed the carbon isotopic composition of the gas and measured related hydrocarbons, including ethane and propane, in some samples. The presence of these heavier gas companions is a classic fingerprint of thermogenic gas produced deep within sedimentary basins, distinguishing it from the isotopically lighter methane that microbes generate. The combined geochemical evidence indicated that much of the methane in the rivers came from geological sources rather than subglacial microbial activity, reinforcing the idea that Svalbard’s bedrock is the primary supplier.

The mechanism linking ice to gas is hydrological. Kleber noted that these glaciers mostly melt on their surfaces, but the meltwater finds its way to the bottom of the glaciers through crevasses and holes, a process known as moulin drainage. Once at the bed, the water interacts with the rocks underneath, and where those rocks contain ancient gas, the water can flush methane out into rivers. In effect, each summer’s melt acts as a pump, drawing surface water down through the ice and pushing methane-laden water out the other side, where it degasses into the atmosphere.

Geology alone, however, did not explain the full pattern. The team found that the physical and thermal state of the glacier bed matters enormously. Glaciers with thawed, wet and actively sliding beds were far more efficient at picking up methane, because liquid water moving along the base can access fractures in the rock and dissolve the gas. Glaciers frozen to their beds were much less connected to the rocks below, and even where methane-rich geology was present, the gas stayed put. This means the subglacial thermal regime acts as a gatekeeper controlling how much ancient carbon can escape.

To map these conditions, the researchers combined river chemistry with ice-penetrating radar surveys conducted on selected glaciers, including winter fieldwork on the ice itself. The radar data allowed them to estimate how much of each glacier bed was thawed and capable of transmitting water. Co-author Leonard Magerl emphasized that the temperature at the base of glaciers is a crucial piece of the puzzle. The biggest methane releases occurred where the right rocks and the right glacier conditions came together, an insight he said can help estimate emissions from other ice-covered regions where direct measurements are lacking.

Scaling their findings across the archipelago, the researchers estimate that land-terminating glaciers on Svalbard may transport roughly 182 to 368 tonnes of methane per year in meltwater, depending on how the estimate is extrapolated. That figure comes in addition to earlier, much larger estimates for methane released by groundwater springs emerging in front of retreating glaciers, which previous iC3 work had uncovered. Even at the lower end, the new pathway represents a widespread and previously undercounted route for ancient carbon to reach the atmosphere, one that standard emissions inventories have not captured.

The broader significance lies in the feedback structure. Methane is a powerful greenhouse gas, and while the amounts documented here are small compared with human-caused emissions from fossil fuels, farming and waste, the pathway is not confined to Svalbard. Similar methane-release mechanisms likely operate in other glaciated regions where ice overlies organic-rich rocks or sediments, including large parts of the Arctic, the Himalayas and Antarctica. As glaciers thin and retreat, more meltwater may reach their beds, increasing contact with fractured rock, sediment and groundwater, and in some places flushing out still more methane in a self-reinforcing loop driven by warming.

The picture is not entirely one-directional, however. Some Svalbard glaciers are actually becoming colder at their beds as they shrink and lose insulating ice thickness. If a glacier becomes frozen to its bed, its ability to flush methane through subglacial rivers may decline, potentially cutting off the pathway even as melting accelerates at the surface. Kleber stressed that future methane release will depend on both geology and glacier change, which makes it essential to know what lies beneath the ice, not only how fast the ice is melting. The study builds directly on earlier iC3 findings that meltwater from a single Svalbard glacier could carry geologic methane from beneath the ice, releasing more methane per unit area than Greenland glaciers. The new work, published open access in Nature Communications, shows that this phenomenon is not an isolated curiosity but a region-wide feature of central Svalbard, strongest where shale-rich geology and thawed glacier beds overlap, and a warning sign for ice-covered landscapes across the warming Arctic.

Subject of Research: Geological methane emissions from meltwater draining Svalbard glaciers

Article Title: New study raises concerns about climate feedback loop as melting Arctic glaciers flush ancient methane from rocks beneath the ice

Article References: New study raises concerns about climate feedback loop as melting Arctic glaciers flush ancient methane from rocks beneath the ice. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Svalbard, glaciers, methane, Arctic, climate feedback loop, subglacial hydrology, shale, greenhouse gas, Nature Communications, glacier meltwater, geological methane, polar research