SYLLABUS

GS-1: Salient features of world’s physical geography; Important Geophysical phenomena.

GS-3: Conservation, environmental pollution and degradation.

Context: A recent study by researchers from IISER Pune, Wadia Institute of Himalayan Geology and IIT-Roorkee has found that the rapidly eroding, glaciated upper Indus basin in the northwestern Himalaya acts as a net source of CO₂ due to pyrite oxidation.

Key Findings of the Study

• Pyrite-driven CO₂ release: Researchers analysed 61 water samples from the Indus headwaters and tributaries collected during July–August 2021. Around 68% of sulphate in the upper Indus basin was linked to pyrite oxidation.
  Pyrite, or “fool’s gold”, reacts with oxygen and water to produce sulphuric acid, which can weather carbonate rocks and release CO₂. 
• Net CO₂ source: Pyrite oxidation releases about 4.4 × 10⁵ mol CO₂/km²/year, while silicate weathering removes around 1.4 × 10⁵ mol CO₂/km²/year, making the upper mountainous basin a net CO₂ source.
• Role of erosion and glaciers: Rapid erosion and extensive glacial cover continually expose fresh rock surfaces, facilitating the oxidation of pyrite and accelerating associated weathering reactions.
• Spatial variation: The study found that while the upper mountainous basin is a net CO₂ source, downstream floodplain regions show net CO₂ uptake, highlighting strong spatial variation in the carbon balance.

Understanding the Carbon Cycle and Rock Weathering

• Rock weathering as a CO₂ sink: Rainwater containing dissolved CO₂ reacts with silicate rocks, breaking them down and transferring carbon through rivers towards the oceans. Thus, silicate weathering generally acts as a CO₂ sink over geological timescales.
• The hidden pathway: Himalayan rocks also contain pyrite (FeS₂). When exposed to oxygen and water, pyrite oxidises and produces sulphuric acid, which can react with carbonate rocks and release CO₂.
• Why erosion matters: Rapid erosion exposes fresh minerals, accelerating both CO₂-consuming silicate weathering and CO₂-releasing pyrite-driven weathering.
• Net carbon balance: The overall effect therefore depends on the balance between these competing processes rather than simply on the rate of rock weathering.

Significance of the Findings

• Refines the carbon-sink narrative: The findings show that Himalayan mountain weathering cannot be assessed only through its CO₂-consuming silicate-weathering pathway.
• Carbon-cycle implications: Pyrite oxidation and sulphuric-acid weathering need to be considered while estimating geological CO₂ fluxes from rapidly eroding mountain regions.
• Importance of spatial variation: The contrasting CO₂ balance between the mountainous upper basin and downstream floodplains highlights the need for basin-specific carbon-cycle assessments.
• Broader Himalayan relevance: The study provides a basis for investigating whether similar processes operate in other Himalayan river systems; the researchers specifically highlight the need for studies in the Ganga and Brahmaputra basins before broader conclusions are drawn.

Way Ahead

• • Expand basin-level studies: Conduct comparable geochemical assessments across the Indus, Ganga and Brahmaputra basins to establish the regional extent of pyrite-driven CO₂ release.
• • Measure the complete carbon balance: Future assessments should jointly quantify silicate weathering, carbonate weathering and pyrite oxidation, rather than estimating CO₂ uptake from silicate weathering alone.
• • Strengthen long-term monitoring: Combine river-water chemistry, sulphur and oxygen isotopes, sediment analysis and erosion rates to track changes in weathering pathways.
• • Improve carbon-cycle models: Incorporate sulphur-driven weathering and erosion–weathering interactions into regional and global models to improve estimates of natural CO₂ sources and sinks.
• • Assess changing Himalayan conditions: Examine how changes in glacier cover, erosion and hydrology may alter mineral exposure and pyrite oxidation over time.