N₂ : Ar, nitrification and denitrification in southern California borderland basin sediments1

The first quantitative observations of dissolved molecular nitrogen (N 2 ) in deep‐sea sedimentary pore waters show increases of up to 17% above adjacent bottom water values. The N 2 : Ar concentration ratio similarly increases. This increase is greater than expected from reduction of seawater nitrate in the sediment. A mechanism is suggested in which ammonia, derived from nitrogen‐containing organic matter, is converted to N 2 through a nitrite intermediate under conditions of low oxygen tension. Ammonia is not converted to N 2 in anoxic sediments that are undergoing sulfate reduction even though N 2 is the thermodynamically stable species.