Nitrification and nitric oxide in the oxygen minimum of the eastern tropical North Pacific

Bettie Ward, O. C. Zafiriou

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Ammonium oxidation rates (VNH4 ), nitric oxide concentrations [NO], and NO formation rates (VNO) were measured below the euphotic zone off Baja California. Vertically integrated nitrification rates were 1.1-2.7 mmol N m-2 d-1, compared with VERTEX estimates (in a less productive nearby region) of 0.56 mmol m-2 d-1 for the loss of sinking organic N between 100 and 2000 m. Integrated ammonium oxidation rates thus may provide valid independent estimates of organic N recycling. NO was detected at picomolar levels in the water column at oxygen concentrations between 0 and 100 μM. Many samples actively generated NO, which required an in situ source, and yielded flux estimates. A crude estimate of the vertically integrated NO flux for the region, 0.19 mmol N m-2 d-1, is 13% of the average integrated nitrification flux, suggesting the NO plays a significant role as an intermediate product in the nitrogen cycle. Most NO and NO production were found in the region of active nitrification outside the zone of active denitrification. However, VNH4 and VNO are interrelated in a complex way that suggests, but does not prove, a link between the two. NO may arise in part from an intermediate compound that is filterable through 0.2 μm filters, possibly a soluble byproduct of nitrification such as hydroxylamine.

Original languageEnglish (US)
Pages (from-to)1127-1142
Number of pages16
JournalDeep Sea Research Part A, Oceanographic Research Papers
Issue number7
StatePublished - Jul 1988

All Science Journal Classification (ASJC) codes

  • General Environmental Science
  • General Earth and Planetary Sciences


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