Wadia Institute of Himalayan Geology, Dehradun, 248001, India.
Department of Geology and Geophysics, I. I. T. Kharagpur, Kharagpur, 721302, India.
Environ Sci Pollut Res Int. 2020 May;27(13):14818-14835. doi: 10.1007/s11356-020-07922-1. Epub 2020 Feb 13.
Evaluation of geogenic carbon fluxes between solid Earth and its atmosphere is essential to understand the global geological carbon cycle. Some of the key geogenic CO suppliers are the magmatic mantle and metamorphic degassing from active and quiescent volcanoes, fault zones, geothermal systems and CO rich groundwater. Indian Himalayan geothermal field hosts about 340 geothermal springs in natural as well as artesian condition that eject hot waters and volatiles with varied temperature and chemical composition. These sites provide an opportunity to analyse tectonically driven gas emissions and their impact on regional and global climate. Here we adopt a method for direct measurement of Dissolved Inorganic Carbon (DIC ≈ HCO) concentration in the geothermal springs to estimate geogenic CO flux from an active region based on water discharge and area of geothermal system between the tectonic boundaries of the Main Central Thrust (MCT) and Main Boundary Thrust (MBT) of the Garhwal (Northwest) Himalaya. In the study area, geothermal spring water contain high δC ratio (- 8.5‰ to + 4.0‰ ), and among the major ions, bicarbonate (HCO) varies by an order of magnitude from 1697 to 21,553 μEq/L; chloride and sodium vary from 90 to 19,171 μEq/L and 436 to 23181 μEq/L. The elevated concentration of Cl and Na in geothermal spring waters suggests affinity towards their deeper origin. These geothermal springs cover a large area of nearly 10,000 km of the Garhwal region showing a significant discharge of CO rich water with an estimated carbon dioxide degassing flux of ~7.2 × 10 mol/year to the atmosphere. Considering widespread occurrences of geothermal springs in tectonically active areas worldwide, the proposed direct measurement of DIC may be used as a reliable tool to estimate CO fluxes in different active orogenic settings within the Earth system. Results of stable isotopes of δO and δD in these geothermal spring waters follow the Global Meteoric Water Line (GMWL), suggesting affinity of their recharge through the meteoric origin.
评估固体地球与其大气之间的地球成因碳通量对于理解全球地质碳循环至关重要。一些主要的地球成因 CO 供应源是岩浆地幔和活动火山、休眠火山、断层带、地热系统和富 CO 地下水的变质脱气。印度喜马拉雅地区拥有约 340 个自然和自流的温泉，这些温泉喷出的热水和挥发物具有不同的温度和化学成分。这些地点提供了一个分析构造驱动气体排放及其对区域和全球气候影响的机会。在这里，我们采用直接测量温泉中溶解无机碳 (DIC≈HCO) 浓度的方法，根据水排放量和主中央逆冲断层 (MCT) 和主边界逆冲断层 (MBT) 之间的地热系统面积，从一个活跃区域估算地球成因 CO 通量，该地区位于北喜马拉雅加瓦尔的（NW）。在研究区域，温泉水含有高 δC 比值（-8.5‰至+4.0‰），主要离子中，碳酸氢根 (HCO) 的变化幅度为 1697 至 21,553 μEq/L；氯和钠的变化范围为 90 至 19,171 μEq/L 和 436 至 23181 μEq/L。温泉水中氯和钠的高浓度表明它们与深部起源有关。这些温泉覆盖了加瓦尔地区近 10,000 公里的大面积，显示出富含 CO 的水大量排放，估计二氧化碳排放量约为 7.2×10 摩尔/年到大气中。考虑到全球构造活跃地区广泛存在温泉，这种直接测量 DIC 的方法可能成为估计地球系统内不同活动造山环境中 CO 通量的可靠工具。这些温泉水中的稳定同位素 δO 和 δD 的结果遵循全球大气水线 (GMWL)，表明它们通过大气降水补给的亲水性。
