Nitrous oxide distribution in the north-eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula)

The distribution of nitrous oxide (N2O) was investigated in the coastal waters of the north-eastern shelf of the Gulf of Cádiz during four campaigns that took place in June 2006, November 2006, February 2007 and May 2007. N2O distributions showed strong temporal fluctuations in both concentration and saturation values, which were significantly higher in June and November 2006 compared to February and May 2007. Measured concentrations ranged from 8.2 to 23.2 nM in surface waters and from 8.9 to 28.5 nM in bottom waters, corresponding to saturations that varied between 105–335% and 100–340%, respectively. Tidal exchange with rivers, creeks and the surrounding salt marshes, together with enhanced drainage during rainy periods, were important factors controlling N2O distribution. The region behaved as a net source of N2O to the atmosphere throughout the year, with mean air–sea fluxes for each survey that varied between 1.0–15.3 µmol N2O m−2 d− 1 and 2.2–25.4 µmol N2O m−2 d− 1, depending on the parameterization used to calculate gas transfer velocities.