The role of the ocean for the global budget of atmospheric nitrous oxide

The oceanic N2O emissions play a major role in the atmospheric N2O budget (see for example Bange, 2006a). In the Fourth Assessment Report of the IPCC, mean annual N2O emissions (ranges are given in parenthesis) of 3.8 (1.8-5.8) X 1012g (Tg) N and 1.7 (0.5-2.9) Tg N were attributed to the open ocean and coastal areas (including rivers), respectively (IPCC, 2007). According to the IPCC report, open ocean and coastal areas (including rivers) represent about 21 per cent and 10 per cent of the total natural and anthropogenic N2O sources of 17.7Tg N yr-1, respectively (IPCC, 2007). There are various reasons for the considerable ranges of uncertainty in the global N2O emission estimates (Bange, 2008):

• different methodological approaches (empirical models versus extrapolation of measurements),

• the application of different air-sea exchange models and

• the fact that the applied classification of coastal areas is not uniform.

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