Nitrite dynamics in the open ocean-clues from seasonal and diurnal variations

Efrat Meeder*, Katherine R.M. MacKey, Adina Paytan, Yeala Shaked, David Iluz, Noga Stambler, Tanya Rivlin, Anton F. Post, Boaz Lazar

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

41 Scopus citations

Abstract

Two alternative mechanisms are suggested for nitrite accumulation in the oxygenated oligotrophic water column: (1) excretion by phytoplankton or (2) microbial oxidation of ammonium (nitrification). This study assessed the role of these 2 mechanisms, based on seasonal and high-resolution diurnal depth profiles of the dissolved inorganic nitrogen (DIN) species (nitrite, ammonium, nitrate) and chlorophyll a in the Gulf of Aqaba, Red Sea. Both mechanisms operated in the water column, but in different seasons; nitrification was the prime process responsible for nitrite accumulation during the stratified summer season and phytoplankton nitrite excretion operated during winter mixing. At the onset of summer stratification two N peaks developed below the photic zone, an ammonium maximum (AM) and below it the primary nitrite maximum (PNM). Both peaks were located at a depth range where phytoplankton are thought to be inactive and not excreting nitrite. During summer stratification, the water column deep chlorophyll maximum (DCM), AM, PNM and the nitracline were ordered by a downward increase in N oxidation state similar to the temporal order of the N-species during nitrification. This similarity, together with the diurnal stability of the PNM and its co-existence with oscillating chlorophyll profiles above the DCM, is consistent with nitrification as the key process forming the PNM. We suggest that transport and reaction control the vertical order and separation of N-species in the water column. The ratios between the rate constants for ammonification, ammonium oxidation, nitrite oxidation and nitrate assimilation were estimated by a simple box model to be 1:3:1.5:0.15, respectively. These field estimates are similar to the ratios between the rate constants measured in laboratory experiments.

Original languageAmerican English
Pages (from-to)11-26
Number of pages16
JournalMarine Ecology - Progress Series
Volume453
DOIs
StatePublished - 7 May 2012

Keywords

  • Ammonium maximum
  • Gulf of Aqaba
  • Nitrification
  • Nitrite
  • Nitrite excretion
  • Primary nitrite maximum
  • Red Sea

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