Origin of methane in the Gulf of Cádiz

  1. A. Sierra 1
  2. D. Jiménez-López 1
  3. T. Ortega 1
  4. A. Delgado-Huertas 3
  5. J.A. Sanabria 1
  6. V. Amaral 12
  7. R. Ponce 1
  8. A. Gómez-Parra 1
  9. J. Forja 1
  1. 1 Dpto. Química-Física, INMAR, Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Campus Universitario Río San Pedro, 11510 Puerto Real, Cádiz, Andalucía, SPAIN.
  2. 2 Ecología Funcional de Sistemas Acuáticos, Centro Universitario Regional Este, Universidad de la Republica, Rocha, Uruguay.
  3. 3 Laboratorio de Biogeoquímica de Isótopos Estables, Instituto Andaluz de Ciencias de la Tierra IACT (CSIC-UGR), Av. de las Palmeras, 4, Armilla, 18100 Granada, SPAIN.
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Actas:
XIX Seminario Ibérico de Química Marina. COMUNICACION ORAL

Editorial: Universidad de Vigo

ISBN: 978-84-8158-790-6

Año de publicación: 2018

Tipo: Aportación congreso

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Resumen

The concentration of CH4 were measured in five transects in the Gulf of Cadiz (Trafalgar, Sancti Petri, Guadalquivir, Tinto y Odiel and Guadiana) in four cruises during Spring, Summer, Autumn and Winter of 2016. Moreover, we sampled in three mud volcanoes (San Petersburgo, Anastasya and Pipoca) situated in the Gulf of Cadiz during two cruises. The concentration of CH4 was obtained by using a gas chromatograph. In addition, the stable carbon isotopic compositions (δ13C) were measured to try to establish the origin of methane in the study area. The mean CH4 value for this area was 9.49 ± 2.4 nM, with large spatial and temporal variations. The highest values were found in June 2016 and the lowest in Spring 2016. In most of the sampling area the highest concentration of CH4 was found in subsurface waters at depths close to the thermocline, and in the bottom waters near the coast. Moreover, the decreased of the gas concentration in thefarthest stations indicated a coastal input. The stable carbon isotopic compositions ranged between -29.2 and -50.7 ‰. The less negative values were associated with the highest CH4 concentrations in the mud volcanoes samples, showing a thermogenic origin of methane (Kim et al., 1984; Brooks et al., 1987; Schoell, 1988) in the gulf of Cadiz. The seawater-airflux of CH4 ranged between 12.4 and 37.7 µmol m−2 d−1, showing that the study area acts as a source of CH4 to the atmosphere. The CH4 fluxes increased with proximity to the coast, with the highest values in summer 2016.