Publicação
Hydrochemical and isotopic composition (87Sr/86Sr) of rainwater from São Miguel (Azores, Portugal)
| Resumo: | Rain chemistry has been the subject of extensive research over the last few decades in order to determine the geochemical mechanisms that control the water composition (e.g., Négrel et al., 2007). In the present work rain samples were collected at Furnas and Fogo volcanoes, located in São Miguel (Fig.1a), in order to characterize the chemical fingerprint of the rainwaters and to investigate a possible interaction with fumarolic gases. The collected samples are plotted along the seawater dilution line in the Na+ vs. Cl- binary plot (Fig.1b). Despite the fact that some samples are close to the line, showing the influence of marine aerosols, the majority, with the exception of CRQ, depict an enrichment in Cl-, representing a local chlorine source (Fig.1b). The chlorine enrichment presented by CC is accompanied by an increment in SO4 2- (Fig.1c), which can be attributed to a volcanogenic origin (Madonia & Liotta, 2009). On the other hand, the other samples show a small increment of Cl-, which can be attributed to the fumarolic contribution, to a third source contribution (e.g., anthropogenic) or to the Cl or Na+ fractionation. The remaining sample show an increment in sodium, which can be attributed to the influence of dust particles. In order to decipher the chemical complexity of the rainwaters the sea salts and terrestrial component were calculated. Sodium was used as a reference element for the sea salt component. The marine origin ranges from 11.5 to 100 % for Cl-, 4.7 to 100 % for SO4 2-, 4.4 to 35.1 % for Ca2+, 64.2 to 90.6 % for Mg2+ and 10.3 to 48.2 % for K+. This demonstrates not only the influence of marine aerosols over the chemistry of these waters, but also the importance of other sources such as fumarolic fluids and mineral dust. Most of the rainwater samples have 87Sr/86Sr that vary from 0.70849 to 0.71027 (Fig.1d) similar or slightly higher than that of the seawater (87Sr/86Sr=0.70918 ± 1; Faure and Mensing, 2005), suggesting that sea salts are the main source of the strontium isotopic ratios. Results are within the range of values presented by rainwater in mainland Portugal (87Sr/86Sr = 0.708965 ± 31 – 0.710345 ± 38; Ribeiro et al., 2014). One sample deviates from these values, exhibiting a lower strontium isotopic ratio (0.70701). This sample is exposed to the fumarolic fluids, which are mainly composed of steam water (e.g., Caliro et al., 2015). The boiling pools that produce the steam have strontium isotopic values ranging from 0.705408 (Caldeira Asmodeu) to 0.705432 (Caldeira Grande; Ferreira et al., 2023). This confirms that the sample results from the mixture between rainwater and fumarolic fluids (Fig.1d), as interpreted from the main elemental hydrogeochemical data. |
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| Autores principais: | Ferreira, L. |
| Outros Autores: | Cruz, J. Virgílio; Viveiros, F.; Durães, N.; Coutinho, R.; Andrade, C.; Santos, J. F. |
| Assunto: | Hydrogeochemistry Precipitation Fumarole 87Sr/86Sr Azores |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | documento de conferência |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | Rain chemistry has been the subject of extensive research over the last few decades in order to determine the geochemical mechanisms that control the water composition (e.g., Négrel et al., 2007). In the present work rain samples were collected at Furnas and Fogo volcanoes, located in São Miguel (Fig.1a), in order to characterize the chemical fingerprint of the rainwaters and to investigate a possible interaction with fumarolic gases. The collected samples are plotted along the seawater dilution line in the Na+ vs. Cl- binary plot (Fig.1b). Despite the fact that some samples are close to the line, showing the influence of marine aerosols, the majority, with the exception of CRQ, depict an enrichment in Cl-, representing a local chlorine source (Fig.1b). The chlorine enrichment presented by CC is accompanied by an increment in SO4 2- (Fig.1c), which can be attributed to a volcanogenic origin (Madonia & Liotta, 2009). On the other hand, the other samples show a small increment of Cl-, which can be attributed to the fumarolic contribution, to a third source contribution (e.g., anthropogenic) or to the Cl or Na+ fractionation. The remaining sample show an increment in sodium, which can be attributed to the influence of dust particles. In order to decipher the chemical complexity of the rainwaters the sea salts and terrestrial component were calculated. Sodium was used as a reference element for the sea salt component. The marine origin ranges from 11.5 to 100 % for Cl-, 4.7 to 100 % for SO4 2-, 4.4 to 35.1 % for Ca2+, 64.2 to 90.6 % for Mg2+ and 10.3 to 48.2 % for K+. This demonstrates not only the influence of marine aerosols over the chemistry of these waters, but also the importance of other sources such as fumarolic fluids and mineral dust. Most of the rainwater samples have 87Sr/86Sr that vary from 0.70849 to 0.71027 (Fig.1d) similar or slightly higher than that of the seawater (87Sr/86Sr=0.70918 ± 1; Faure and Mensing, 2005), suggesting that sea salts are the main source of the strontium isotopic ratios. Results are within the range of values presented by rainwater in mainland Portugal (87Sr/86Sr = 0.708965 ± 31 – 0.710345 ± 38; Ribeiro et al., 2014). One sample deviates from these values, exhibiting a lower strontium isotopic ratio (0.70701). This sample is exposed to the fumarolic fluids, which are mainly composed of steam water (e.g., Caliro et al., 2015). The boiling pools that produce the steam have strontium isotopic values ranging from 0.705408 (Caldeira Asmodeu) to 0.705432 (Caldeira Grande; Ferreira et al., 2023). This confirms that the sample results from the mixture between rainwater and fumarolic fluids (Fig.1d), as interpreted from the main elemental hydrogeochemical data. |
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