15N/14N ratio of dissolved N2O in the eastern tropical Pacific Ocean

Nitrous oxide (N 2 O) is of prime interest for understanding stratospheric chemistry 1 and the energy budget of the troposphere 2 . Atmospheric N 2 O has been considered to be mainly regulated by biological processes in soils 3–6 . However, the oceans have an important role in the geochemical cycle of N 2 O both as a reservoir and a reaction site 7–12 . We report here the first 15 N abundance data on dissolved N 2 O collected from the eastern tropical Pacific Ocean where active nitrogen transformation has been proposed to occur 12–16 . Our 15 N data provide additional evidence for the hypothesis that the subsurface waters act as a source of N 2 O and that the extremely oxygen-depleted waters act as a sink.