NITROUS-OXIDE IN COASTAL WATERS

We determined atmospheric and dissolved nitrous oxide (N2O) in the sur face waters of the central North Sea, the German Eight, and the Girond e estuary. The mean saturations were 104 +/- 1% (central North Sea, Se ptember 1991), 101 +/- 2% (German Bight, September 1991), 99 +/- 1% (G erman Bight September 1992), and 132% (Gironde estuary, November 1991) . To evaluate the contribution of coastal areas and estuaries to the o ceanic emissions we assembled a compilation of literature data. We con clude 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 upw elling regions are included, a computation of the global oceanic N2O f lux indicates that a considerable portion (approximately 60%) of this flux is from coastal regions, mainly due to high emissions from estuar ies. We estimate, using two different parameterizations of the air-sea exchange process, an annual global sea-to-air flux of 11-17 Tg N2O. O ur results suggest a serious underestimation of the flux from coastal regions in widely used previous estimates.