Nitrous oxide measurements in the eastern tropical Pacific Ocean

Abstract

In March 1976 the first N,O measurements were made in the sea water and marine air of the eastern tropical Pacific Ocean during a cruise from San Diego, California, to San Martin, Peru. Continuous measurements of N,O in the marine atmosphere were made throughout the duration of the cruise. The tropospheric mixing ratio was 332 f 9 p.p.b. v/v N,O. The concentration of N,O in the marine air appeared to show a direct relationship to the N,O concentration in the surface sea water, with the highest N,O mixing ratios over regions which were highly supersaturated, off the coasts of Baja California and Peru, and in the equatorial upwelling region. The surface sea water samples were generally supersaturated with N,O, with an average saturation of 145% relative to the marine atmosphere. The average flux of N,O from the surface sea water into the atmosphere was 0.5 x s-I. Only one surface sea water sample showed significant undersaturation; the other 28 surface water samples were approximately saturated or supersaturated. Water samples were also collected down to depths of 300 m during seven hydrocast stations. The stations showed two distinct distribution patterns for N,O concentration versus depth for the region between the surface and 300 m. At five of the seven stations the N,O concentration increased rapidly from the surface to a depth of 100 m, and then remained relatively constant down to the maximum depth of 300 m. At the other two stations the N,O concentration showed the same rapid increase between the surface and 75-100 m, but then the N,O concentration decreased in the next 5&75 m until the concentration of N,O at 150 m was lower than that found at the surface. At these two stations the water from 150 m to 300 m was just saturated or undersaturated with N,O with respect to the atmosphere. These two stations were located in the oxygen-deficient region off the coast of Mexico, which suggests that the low N,O concentrations below the thermocline may be due to denitrification. However, stations in the oxygen-deficient region off the coast of Peru showed considerable N,O supersaturation at all depths. Recent results indicate that the role of N,O in the nitrogen cycle of the ocean may be more complex than has previously been suggested. g N,O 004(12826/80/010056-17$02.50/0 @ 1980 Munksgaard, Copenhagen Tellus 32 (1980), 1

Factors governing the oceanic nitrous oxide distribution: Simulations with an ocean general circulation model

“…This reduction of nitrate to ammonium is most likely to be carried out by phytoplankton in the marine environment and has been suggested as an alternative source of N20 in the surface ocean. The studies of Hahn [1981], Pierotti and Rasmussen, [1980] and Oudot et al [1990] invoke this mechanism to account for very high surface N20 levels in upwelling zones. There is, however, no direct support for such conclusions, and Goteau et al [1980] found no evidence of N20 release from cultures of phytoplankton; furthermore, Cohen and Gordon [1979] note that if such a source exists, it is probably of relatively small magnitude.…”

Austral summer N2O sink and source characteristics and their impact factors in Prydz Bay, Antarctica

“…Oceanic N 2 O has been widely studied since the 1960s, and its basic distribution patterns in the Atlantic Ocean [Junge and Hahn, 1971], the Pacific Ocean [Butler et al, 1989;Cline et al, 1987;Codispoti and Christensen, 1985;Cohen and Gordon, 1978;Pierotti and Rasmussen, 1980;Singh et al, 1979;Yoshida et al, 1984], and the Arabian Sea [Bange et al, 1996;Naqvi and Noronha, 1991] have been well described. N 2 O emission hotspots such as the Eastern Tropical Pacific and the Arabian Sea were discovered during this period, and their significant contributions to the global N 2 O budget have been comprehensively studied.…”

Experimental examination on nitrous oxide accumulation during nitrification in a freshwater lake.

“…However, some uncertainties remain as to the role of nitrification in N20 formation in aquatic environments. AOU is merely a measure of the total biological oxygen utilization and oxidation of ammonium or organic amines accounts for only a minor part of the oxygen consumption (PIEROTTI and RASMUSSEN, 1980 ) .…”