Sarath Pullyottum Kavil, Jean Riotte, Ramananda Chakrabarti, V. V. S. S. Sarma, B. S. K. Kumar, J. Prunier, Arnaud Dapoigny, Damien Cardinal
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The coastal groundwater δ<sup>30</sup>Si values do not show any dependence on regional aquifer lithology. However, the permeable coastal alluvial groundwaters exhibit the highest variability in DSi and δ<sup>30</sup>Si, likely acquiring signatures of shallow surface/subsurface processes through mixing. A broad negative correlation between δ<sup>30</sup>Si values and the Ge/Si ratio is best explained by the partitioning of Si into secondary minerals phases within the weathering zone. The majority of coastal groundwater follows a steady-state model evolution, indicating a dynamic equilibrium between Si supply and the formation of secondary phases. In regions of low annual rainfall, groundwater irrigation can lead to infiltration of return flow water to aquifer systems, leading to their heavy δ<sup>30</sup>Si values. The fresh submarine groundwater discharge along the Indian coast is estimated to be 2.1 GmolSi yr<sup>−1</sup>, which is less than 1% of the riverine Si flux to the North Indian Ocean and 0.3% of the global fresh groundwater Si flux.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5000,"publicationDate":"2025-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GB008706","citationCount":"0","resultStr":"{\"title\":\"Heterogenous Si Isotopic Composition in Coastal Groundwater: Controls on Dissolved Silicon and Groundwater Discharge Along Indian Coastline\",\"authors\":\"Sarath Pullyottum Kavil, Jean Riotte, Ramananda Chakrabarti, V. V. S. S. Sarma, B. S. K. Kumar, J. 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引用次数: 0
摘要
我们报告了在印度海岸收集的80多个地下水样本的稳定硅同位素比值(δ30Si),涵盖了广泛的含水层岩性(冲积岩、玄武岩、变质岩、红土和石灰岩)、气候(半干旱到热带潮湿)和土地利用环境。印度沿海地下水溶解硅(DSi) (80 ~ 1350 μM)和δ30Si值(- 1.1‰~ 4.5‰)具有较大的空间变异性。平均而言,印度沿海地下水的δ30Si值(0.8±1.1‰,1SD, n = 85)与全球公布的地下水δ30Si值(0.8±0.8‰,n = 117)相当,显著低于印度河流的δ30Si组成。沿海地下水δ30Si值不受区域含水层岩性的影响。然而,渗透性沿海冲积地下水的DSi和δ30Si变化最大,可能是通过混合获得了浅层/地下过程的特征。δ30Si值与Ge/Si比值呈广泛的负相关关系,最好的解释是在风化带内,Si被划分为次级矿物相。大部分沿海地下水遵循稳态模式演化,表明Si供应与次生相形成之间存在动态平衡。在年降雨量少的地区,地下水灌溉会导致回流水入渗到含水层系统中,导致其δ30Si值较大。据估计,沿印度海岸的新鲜海底地下水排放量为2.1 GmolSi yr - 1,不到流入北印度洋的河流Si通量的1%和全球新鲜地下水Si通量的0.3%。
Heterogenous Si Isotopic Composition in Coastal Groundwater: Controls on Dissolved Silicon and Groundwater Discharge Along Indian Coastline
We report stable silicon isotope ratio (δ30Si) of over 80 groundwater samples collected along the Indian coast, spanning a wide range of aquifer lithologies (alluvial, basalt, metamorphic, laterite and limestone), climate (semi-arid to tropical wet) and land use settings. Indian coastal groundwater exhibits large spatial variability in dissolved silicon (DSi) (80–1350 μM) and δ30Si values (−1.1‰ to 4.5‰). On average, the δ30Si value of the Indian coastal groundwater (0.8 ± 1.1‰, 1SD, n = 85) is comparable to published groundwater globally (0.8 ± 0.8‰, n = 117), and significantly lower than Indian riverine δ30Si composition. The coastal groundwater δ30Si values do not show any dependence on regional aquifer lithology. However, the permeable coastal alluvial groundwaters exhibit the highest variability in DSi and δ30Si, likely acquiring signatures of shallow surface/subsurface processes through mixing. A broad negative correlation between δ30Si values and the Ge/Si ratio is best explained by the partitioning of Si into secondary minerals phases within the weathering zone. The majority of coastal groundwater follows a steady-state model evolution, indicating a dynamic equilibrium between Si supply and the formation of secondary phases. In regions of low annual rainfall, groundwater irrigation can lead to infiltration of return flow water to aquifer systems, leading to their heavy δ30Si values. The fresh submarine groundwater discharge along the Indian coast is estimated to be 2.1 GmolSi yr−1, which is less than 1% of the riverine Si flux to the North Indian Ocean and 0.3% of the global fresh groundwater Si flux.
期刊介绍:
Global Biogeochemical Cycles (GBC) features research on regional to global biogeochemical interactions, as well as more local studies that demonstrate fundamental implications for biogeochemical processing at regional or global scales. Published papers draw on a wide array of methods and knowledge and extend in time from the deep geologic past to recent historical and potential future interactions. This broad scope includes studies that elucidate human activities as interactive components of biogeochemical cycles and physical Earth Systems including climate. Authors are required to make their work accessible to a broad interdisciplinary range of scientists.