Selected Trades Biome Ecosystem Processes

Nitrous oxide (N2O) is a potent greenhouse gas (approximately 200 times more effective than CO2 on a molar basis) that has also been implicated in stratospheric ozone depletion (Kim and Craig, 1990 Yoshida et al., 1989) (see Bange, Chapter 2, this volume). Currendy, N2O accounts for about 5.5% of the enhanced radiative forcing attributed to all gases in the atmosphere (IPCC, 2007). Furthermore, while the atmospheric inventory of N2O is increasing, its sources are not well understood causing a renewed interest in the role of marine ecosystems as a potential source for N2O. 

Near-surface ocean nitrification at rates that are Hkely to exceed the upward eddy-diffusion of NOa from beneath the euphotic zone (e.g., Martin and Pondaven, 2006) has important implications for both the conceptual model of new vs. regenerated production (Dugdale and Goering, 1967) and for the 

Structure and dynamics of the primary and secondary nitrite maximum layers 

Nitrite-N (N02 ) has an intermediate redox position between that of NH4 and N03, thus N02 often accumulates in selected depth strata when active N transformations are occurring (Rakestraw, 1936 Vaccaro and Ryther, 1960). In the global ocean, two such zones have been identified and studied (Fig. 16.11) (1) the primary N02 maximum (PNM) zone that is usually located near the base of the euphotic zone worldwide and (2) the secondary N02 maximum (SNM) zone that is most prominent in oxygen depleted waters (Codispoti and Richards, 1976 Fiadeiro and Strickland, 1968). 

The formation and maintenance of the PNM appears to be complex, perhaps involving at least three independent and, in part, competing processes that include  

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