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Nitrous oxide in the Somali Basin: the role of upwelling
de Wilde, H.P.J.; Helder, W. (1997). Nitrous oxide in the Somali Basin: the role of upwelling. Deep-Sea Res., Part 2, Top. Stud. Oceanogr. 44(6-7): 1319-1340
In: Deep-Sea Research, Part II. Topical Studies in Oceanography. Pergamon: Oxford. ISSN 0967-0645, more
Peer reviewed article  

Also published as
  • de Wilde, H.P.J.; Helder, W. (1997). Nitrous oxide in the Somali Basin: the role of upwelling, in: de Wilde, H.P.J. (1999). Nitrous oxide and methane in marine systems. : pp. 1319-1340, more

Available in Authors 

Keywords
    Nitrous oxide; Upwelling; ISW, Somali Basin; Marine

Authors  Top 
  • de Wilde, H.P.J.
  • Helder, W.

Abstract
    Nitrous oxide (N2O) concentrations in surface water, resulting emissions into the atmosphere, and the distribution in the water column were measured in the Somali upwelling region and the Gulf of Aden during July-August 1992. The N2O concentration in the water column exhibited two maxima: a sharp subsurface maximum around 100-200 m, and a broad deep-water maximum around 600-1000 m. Both maxima intensified northward, reaching concentrations up to 81 nM (1030% saturation) and 76 nM (840% saturation), respectively. Deep-water N2O was correlated negatively with O2 and positively with nitrate, indicating microbial N2O production by nitrification. At O2 concentrations below 15-20 µM, the ratio between N2O production and O2 consumption increased significantly, suggesting an increasing N2O yield in the nitrification process. Oxygen concentrations, however, never dropped low enough to allow N2O cycling by denitrification.Surface water N2O saturation was strongly negatively correlated with temperature, indicating that monsoon-driven upwelling of cold N2O-rich water controlled the saturation degree of N2O in surface waters. The maximum N2O saturation was 330% in freshly upwelled waters. The strong monsoon wind driving the upwelling concomitantly induced strong vertical mixing and effective air-sea gas exchange. As a consequence of the simultaneous occurrence of strong N2O saturations and high gas transfer velocities, N2O emissions into the atmosphere reached maximum values of 260-500 µmol m-2 day-1, which is nearly three orders of magnitude above the global mean oceanic N2O flux. Between 21 June and 25 August 1992, the N2O emission from the region of most intense upwelling off Somalia was estimated at (0.6-1.1) x 10(9) mol [(26-48) x 10(9) g]. Although this flux equals 0.4-0.8% of the estimated annual marine N2O emission, it was emitted during a timespan of 2 months from an area of less than 0.011% of the World Ocean.

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