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Himalayan Geothermal Springs release huge amount of carbon dioxide in atmosphere

Wadia Institute of Himalayan Geology (WIHG), an autonomous institute under the Department of Science & Technology, Govt. of India, which investigated and characterized the gas emissions from Himalayan geothermal springs, found that these springs which cover about 10,000 square km in the Garhwal region of Himalaya show a significant discharge of Carbon dioxide (CO2). The estimated carbon dioxide degassing (removal of dissolved gases from liquids, especially water or aqueous solutions) flux is nearly 7.2 ×10 6 moles/year to the atmosphere. The study published in the scientific journal Environmental Science and Pollution Research suggested that CO2 in these thermal springs are sourced from metamorphic decarbonation of carbonate rocks present deep in the Himalayan core along with magmatism and oxidation of graphite. Most of the geothermal water is dominated by evaporation followed by weathering of silicate rocks. Isotopic analyses further point towards a meteoric source for geothermal water.

The team of scientists from WIHG carried out detailed chemical and stable isotope analysis of water samples collected from 20 geothermal springs from major fault zones of Garhwal Himalaya. Further, the isotopic measurements (identification of the abundance of certain stable isotopes and chemical elements within organic and inorganic compounds) such as Dissolved Inorganic Carbon (δ 13 C DIC ), and Oxygen (δ 18 O) along with major ions were analysed for all the samples. 

They found that the geothermal spring water contains high Dissolved Inorganic Carbon δ 13 C DIC ratio (−8.5‰ to + 4.0‰VPDB), and among the major ions, bicarbonate (HCO 3 − ) varied between 1697 to 21,553 μEq/L; chloride and sodium ranged between 90 to 19,171 μEq/L and 436 to 23181 μEq/L. A high concentration of chloride (Cl − ) and sodium (Na + ) in geothermal spring waters indicated its deeper source and strong signature of carbon outgassing. 

Simulation studies done by the scientists of WIHG suggest that these geothermal springs have the potential to degas ~7.2 × 10 6 moles of CO 2 per year to the atmosphere. Estimated flux from this study is comparable to the release of CO 2 during the uplift of the Himalaya (~10 11 moles/year) and sub-aerial volcanism (10 12 moles/year) in the atmosphere. Such CO 2 degassing should be taken into account to assess global carbon outflux in the earth’s atmosphere.

– Tapas Bhattacharya

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