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Marine Ecology Progress Series

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MEPS 453:11-26 (2012)  -  DOI:

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

Efrat Meeder1,2,*, Katherine R. M. Mackey3, Adina Paytan3, Yeala Shaked1,2, David Iluz4,5, Noga Stambler4, Tanya Rivlin2, Anton F. Post2, Boaz Lazar1,2

1Ferdy and Nadine Hermann Institute of Earth Sciences, Hebrew University, Edmond J. Safra Campus, Jerusalem 91904, Israel
2Interuniversity Institute for Marine Sciences Coral Beach, PO Box 469, 88103 Eilat, Israel
3Institute of Marine Science, University of California Santa Cruz, Santa Cruz, California 95064, USA
4Mina & Everard Goodman Faculty of Life Sciences, and 5Department of Geography and Environment, Bar-Ilan University, Ramat-Gan 52900, Israel

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.

KEY WORDS: Nitrite · Nitrification · Nitrite excretion · Primary nitrite maximum · Ammonium maximum · Gulf of Aqaba · Red Sea

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Cite this article as: Meeder E, Mackey KRM, Paytan A, Shaked Y and others (2012) Nitrite dynamics in the open ocean—clues from seasonal and diurnal variations. Mar Ecol Prog Ser 453:11-26.

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