Coupled water-atmosphere exchange of greenhouse gases in the Gulf of Cádiz

Laburpena

Continental platforms act, all in all, as systems that capture part of the anthropogenic carbon dioxide (CO2) from the atmosphere and emit methane (CH4) and nitrous oxide (N2O). If we consider the different Global Warming Potential of these gases, we can find some controversy on the effect of the exchange combination of these gases on the radioactive capacity of the atmosphere. This paper presents the seasonal evolution of the joint emissions of CO2, CH4 and N2O in the Gulf of Cádiz from 2014 to 2016. The database corresponding to the fluxes with the atmosphere for the years 2014 and 2015 are part of the works of Sierra et al. (2107a, b) and Jiménez-López et al. (2019). Additionally, CH4 emissions in 2016 have been described by Sierra et al. (2020). As a new database, the seasonal variations of the CO2 (pCO2) partial pressure distribution and the N2Oconcentration during 2016, as well as their corresponding water-atmosphere fluxes, are included. In 2016, the pCO2 in surface waters showed a linear variation with temperature (8.0 µatm °C-1) and chlorophyll concentration (r2=0.42), in addition to a mean flux to the atmosphere of -0.17 ± 4.21 mmol m-2 d-1. On the other hand, the relationships between the N2O concentrations with the Apparent Oxygen Utilization (r2=0.68) and nitrateconcentration (r2=0.84) indicate a production by nitrification in the water column, which generates a mean flow to the atmosphere of 0.8 ± 0.3 μmol m-2 d-1. For the 2014-2016 period, average annual emissions have been estimated in the studied area of the Gulf of Cadiz (69.1·102 km2) resulting in 23.7 Gg CO2 y -1, 0.5 Gg CH4 y -1 and 0.1 Gg N2O y-1.