Nitrification rates and 15N abundances of N2O and NO3− in the western North Pacific

Distributions and sea-to-air fluxes of nitrous oxide in the South China Sea and the West Philippines Sea

“…N 2 O yield from nitrification in the SCS herein slightly exceeded 0.065% in the shelf region of the SCS (Han et al, 2013), and was also higher than the WPS. N 2 O yields of nitrification in both the SCS and the WPS are higher than those reported elsewhere for the North Pacific Ocean (range, 0.004-0.027%; Yoshida et al, 1989), the NE subarctic Pacific Ocean (range, 0.028-0.040%; Grundle et al, 2012), and the subtropical Atlantic Ocean (0.030-0.040%; Walter At depths greater than that of the maximum N 2 O concentration, the linear relationships between ΔN 2 O and AOU (Fig. 11a) as well as ΔN 2 O and NO 3 À (Fig.…”

“…10b) estimates of the amount of N 2 O that is generated per amount of DO consumed (Nevison et al, 2003;Walker et al, 2010). N 2 O yields from nitrification can be estimated from the DO consumption per mole of N 2 O produced (Grundle et al, 2012), following the Redfield stoichiometry (Redfield et al, 1963), which attributes approximately 17.3% of the total DO consumption to the NH 4 þ oxidation (Ward, 2008 [AOU] À 2.81, n¼ 179, r 2 ¼ 0.91) were also found, owing to nitrification in both the WPS and the SCS, as were also found in the western North Pacific (Yoshida et al, 1989). Hence, N 2 O yields of nitrification could be estimated directly from the molar ratio of N 2 O production to NO 3 À production, which was 0.053 7 0.001% for the WPS and 0.0707 0.002% for the SCS from a depth of 100 m to the depth of the maximum N 2 O concentration.…”

Nitrous oxide in the North Atlantic Ocean

“…Due to the occurrence of linear relationships between N 2 O and AOU and between N 2 O and nitrate we conclude that nitrification might be the major pathway of N 2 O formation in the tropical Atlantic Ocean (Yoshida et al, 1989). Like N 2 O, N 2 O showed an increasing trend from West to East indicating that nitrification is more pronounced in the eastern than the western basin of the tropical Atlantic.…”

“…Many organisms are able to switch between different pathways depending on environmental conditions, and also the yield of N 2 O during a process depends on environmental conditions (Goreau et al, 1980;Poth and Focht, 1985;Richardson, 2000). Positive correlations of N 2 O with apparent oxygen utilization (AOU) or nitrate are interpreted as production of nitrous oxide by nitrification (Yoshinari, 1976;Cohen and Gordon, 1978;Yoshida et al, 1989). However, the dominant production pathway for N 2 O on the global scale and the contribution of different pathways still remains unclear (Codispoti et al, 2001;Popp et al, 2002).…”

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

“…Since N20 was known to be an intermediate product in the denitrification of nitrate to gaseous nitrogen, and denitrification was already established as an important source of N20 in soils, studies in the 1970s proposed that this mechanism was respon- In view of the above evidence, the prevalent view established during the 1980s, and widely accepted today, is that N20 is formed by nitrification processes in oxygenated water and consumed by denitrification in anoxic zones. However, this view is not universal and some studies still uphold denitrification as the primary pathway for N20 formation [e.g., Yoshida et al, 1989]. …”