Pune: The glaciated upper Indus basin in the northwestern Himalayas releases more carbon dioxide (CO2) than it absorbs, making the rapidly eroding mountain region a net source of the greenhouse gas. This finding comes from a new study conducted by researchers from IISER Pune, Wadia Institute of Himalayan Geology, and IIT Roorkee.The study revealed that the release of CO2 caused by the oxidation (or “rusting”) of pyrite—commonly known as “fool’s gold”—is significantly higher than the amount of CO2 absorbed through the weathering of silicate rocks. This challenges the long-held view that chemical weathering in the Himalayas acts primarily as a natural sink for atmospheric CO2.Researchers examined the upper Indus catchment to understand how regional rocks and water affect the carbon cycle. They collected 61 water samples from the Indus headwaters and its tributaries during July and August 2021, analysing their chemical composition and sulfur and oxygen isotopes.The study found that about 68% of the sulphate in the upper Indus basin is linked to pyrite oxidation. In the mountainous region, this process releases about 4.4 × 10⁵ moles of CO2 per square km every year, while silicate weathering uptakes about 1.4 × 10⁵ units. Consequently, the researchers identified a clear net release of CO2 from the upper basin.“Pyrite oxidation is playing a much larger role than previously recognised in the upper Indus basin,” said lead researcher Rakesh Kumar Rout of IISER Pune.The process is relatively straightforward: pyrite is a sulphide mineral found in Himalayan rocks. When it comes into contact with oxygen and water, it oxidizes and produces sulphuric acid. This acid then reacts with carbonate rocks, releasing CO2 into the atmosphere.While the weathering of silicate rocks, such as granite and basalt, can remove CO2 from the atmosphere, the researchers found that this removal is insufficient to offset the release caused by pyrite oxidation in the upper Indus region.The study linked the high rates of pyrite oxidation to the region’s unique geology, rapid erosion, and extensive glacial cover. Glaciers and erosion continually expose fresh rock surfaces, allowing pyrite to react more easily with the elements.Interestingly, the researchers also found that this effect changes as the Indus moves toward the plains. While the mountainous upper basin acts as a net source of CO2, the lower floodplain regions show a net CO2 uptake.“This finding shows that glacier-fed mountain rivers can be important geological sources of CO2,” said co-researcher Gyana Ranjan Tripathy of IISER Pune.The researchers noted that these findings are crucial for understanding how the Himalayas have influenced Earth’s climate over geological timescales. They cautioned, however, that while this study covers the northwestern Himalayan region, similar research is needed in other Himalayan river basins, such as the Ganga and Brahmaputra, to provide a more comprehensive global picture.
