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Quantification of diffuse CO2 flux emission from the crater lagoon of Vila Franca do Campo Islet (São Miguel, Azores)

2023; Springer Science+Business Media; Volume: 85; Issue: 4 Linguagem: Inglês

10.1007/s00445-023-01639-y

1432-0819

César Andrade, Vittorio Zanon, Fátima Viveiros, J. Virgílio Cruz, Adriano Pimentel, Rui Coutinho,

Marine and coastal ecosystems

Abstract To investigate unexplored areas and apply methodologies suitable for monitoring volcanic activity, a pioneer study was undertaken in the crater lagoon of Vila Franca do Campo Islet to identify possible CO 2 degassing zones in the marine environment. This study was carried out using a floating accumulation chamber, which to the best of our knowledge, has only been applied to lacustrine environments. A survey was carried out in the crater lagoon in August 2017, resulting in a total of 143 CO 2 flux measurements. Other parameters, such as water temperature, pH, electrical conductivity, and depth, were also determined at each measuring point, covering a study area of 0.02 km 2 . At one of the deepest sites with higher CO 2 flux values, water samples were collected at depth for determination of stable isotopic composition. Water temperatures ranged between 21.0 and 27.0 °C, pH from 8.24 to 8.89, and electrical conductivity from 52.5 to 53.9 mS/cm. As expected, due to the marine water composition, sampled waters are of the Na-Cl type. CO 2 flux varied between 0.581 and 1.0 g m -2 d -1 (average = 2.967 g m -2 d -1 ). A single CO 2 population, characterized by low CO 2 fluxes, points to a biogenic CO 2 origin (δ 13 C = −9.62‰). The estimated value for the total CO 2 emitted from the water surface is 0.05 t d -1 . CO 2 flux measurements were also compared with the structural features that cross the tuff cone, but no clear relation was observed with fractures/faults. This methodology should be applied to other coastal marine areas, especially where anomalous gas emissions have been reported.