Nitrous oxide in the ocean

Concentrations of dissolved N2O are usually expressed as nmol litre 1 or nmol kg 1. The degree of N2O saturation (given in per cent) is defined as the ratio of the measured N2O concentration to the theoretical N2O equilibrium concentration. The equilibrium concentration in turn depends on the water temperature, salinity, ambient air pressure and the atmospheric N2O dry mole fraction at the time when the water mass was last in contact with the atmosphere (Weiss and Price, 1980). An N2O surface saturation of 100 per cent indicates that the water phase is in equilibrium with the overlying atmosphere. N2O saturation values <100 per cent indicate undersaturation (i.e. uptake of N2O into the water phase when measured in the ocean surface layer) whereas saturation values >100 per cent stand for supersaturation (i.e. N2O

release from the water phase to the atmosphere when measured in the ocean surface layer). The N2O excess (or N2O anomaly) is defined as the difference between the measured N2O and the theoretical N2O equilibrium value. It can be expressed either as a difference in concentration units, A[N2O], or as a difference in partial pressures, ApN2O.

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