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.