Himalayan Erosion and Hidden CO₂ Release

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A study by researchers from IISER Pune, Wadia Institute of Himalayan Geology and IIT-Roorkee, published in Chemical Geology, has identified rapid Himalayan erosion as a significant geological source of atmospheric CO₂.
The study focused on the upper Indus basin and found that CO₂ released through pyrite oxidation can outweigh the CO₂ absorbed through silicate weathering.
CO₂ oxidation rates were estimated to be around three times higher than CO₂ uptake by silicate weathering in the studied region.
The finding challenges the conventional view that intensified Himalayan erosion necessarily acts as a long-term carbon sink.

The collision of the Indian and Eurasian plates causes continuous Himalayan uplift, exposing fresh rocks and minerals to weathering.
Normally, exposure of fresh silicate rocks accelerates silicate weathering, which removes atmospheric CO₂ and stores carbon over geological timescales.
Rapid erosion also exposes pyrite (iron sulphide), commonly known as “fool’s gold”, to oxygen and water.
Pyrite oxidation produces sulphuric acid, which reacts with carbonate rocks and releases CO₂ into the atmosphere.
Thus, erosion can simultaneously:

Silicate weathering is a major component of the long-term global carbon cycle and acts as a natural climate-regulating mechanism.
Atmospheric CO₂ dissolves in rainwater to form weak carbonic acid, which reacts with silicate minerals.
The weathering process produces dissolved bicarbonate and other ions that are transported by rivers to oceans.
Carbon can eventually be stored in marine sediments and carbonate rocks for millions of years, reducing atmospheric CO₂.
Increased temperature and rainfall generally accelerate chemical weathering, creating a long-term negative feedback on global warming.
Himalayan uplift has historically increased exposure of fresh silicate rocks and therefore contributed to enhanced CO₂ drawdown.

Glacial erosion intensifies the process by mechanically crushing rocks and exposing fresh mineral surfaces, including pyrite.
Steep mountainous regions of the upper Indus basin were found to act as net CO₂ sources because pyrite oxidation can dominate the carbon cycle there.
In contrast, flatter downstream floodplains can function as net CO₂ sinks due to greater CO₂ uptake through weathering.
Researchers used sulphur and oxygen isotope ratios in the Indus river system to distinguish different sources of sulphate and identify the contribution of pyrite oxidation.
The study demonstrates that the climatic impact of erosion depends on the type of minerals exposed and the subsequent chemical reactions.

The findings show that mountain erosion is not simply a carbon sink; it can have opposing effects on atmospheric CO₂.
Pyrite oxidation represents a previously underappreciated geological pathway through which erosion can contribute to long-term CO₂ release.
The interaction between tectonic uplift, glaciers, erosion, mineral weathering and river transport is therefore important for understanding the global carbon cycle.
Over geological timescales, such processes can influence Earth’s climate and partially offset the cooling effect traditionally attributed to enhanced silicate weathering.
The Himalayan region consequently provides an important natural laboratory for studying interactions between geomorphology, geology and climate.