Nitrous oxide in coastal waters

We determined atmospheric and dissolved nitrous oxide (N2O) in the surface waters of the central North Sea, the German Eight, and the Gironde estuary. The mean saturations were 104 +/- 1% (central North Sea, September 1991), 101 +/- 2% (German Bight, September 1991), 99 +/- 1% (German Bight September 1992), and 132% (Gironde estuary, November 1991). To evaluate the contribution of coastal areas and estuaries to the oceanic emissions we assembled a compilation of literature data. We conclude that the mean saturations in coastal regions (with the exception of estuaries and regions with upwelling phenomena) are only slightly higher than in the open ocean. However, when estuarine and coastal upwelling regions are included, a computation of the global oceanic N2O flux indicates that a considerable portion (approximately 60%) of this flux is from coastal regions, mainly due to high emissions from estuaries. We estimate, using two different parameterizations of the air-sea exchange process, an annual global sea-to-air flux of 11-17 Tg N2O. Our results suggest a serious underestimation of the flux from coastal regions in widely used previous estimates.