Abstract
We present an 8‐yr time‐series of monthly water column N 2 O measurements from Saanich Inlet, a seasonally anoxic fjord in southern British Columbia. We document seasonal and inter‐annual variability in N 2 O concentrations driven by physical and biological forcing, and examine the relationship between N 2 O and O 2 concentrations across the redoxcline in this system. Near‐surface N 2 O concentrations were typically supersaturated, and increased with depth to a maximum near the oxic‐anoxic transition. Genes associated with both the nitrification and denitrification pathways were widely distributed throughout the water column, suggesting the potential for simultaneous N 2 O production from nitrification and incomplete denitrification. Maximum N 2 O concentrations in Saanich Inlet were similar to other anoxic basins, but lower than those previously documented in coastal upwelling and open ocean oxygen minimum zones. N 2 O and O 2 were inversely correlated throughout the water column, except below 10 μmol O 2 L −1 where net N 2 O consumption appears to occur. In surface waters, maximum N 2 O concentrations and sea–air fluxes occurred during late summer/early fall, when O 2 levels in the oxycline were low. Annual deep basin renewals often persisted over multiple months, supplying O 2 , , and N 2 O to the deep basin, with N 2 O subsequently declining to undetectable levels ( 2 O L −1 ) by late spring. An unusually weak renewal was observed during 2009, possibly linked to reduced upwelling off the coast of British Columbia during El Niño. Our results can be used as a baseline to identify the effect of longer‐term changes in Saanich Inlet, such as deoxygenation and its effect on N 2 O concentrations.