A critical review of the 15 N 2 tracer method to measure diazotrophic production in pelagic ecosystems Limnology and Oceanography: Methods

Dinitrogen (N 2)fixation is an important source of biologically reactive nitrogen (N) to the global ocean. The magnitude of this flux, however, remains uncertain, in part because N 2fixation rates have been estimated fol- lowing divergent protocols and because associated levels of uncertainty are seldom reported —confounding com- parison and extrapolation of rate measurements. A growing number of reports of relatively low but potentially significant rates of N 2fixation in regions such as oxygen minimum zones, the mesopelagic water column of the tropical and subtropical oceans, and polar waters further highlights the need for standardized methodologicalprotocols for measurements of N