Low contribution of N2 fixation to new production and excess nitrogen in the subtropical northeast Atlantic margin

Benavides, Mar; Arı́stegui, Javier; Agawin, Nona S. R.; Álvarez-Salgado, Xosé A.; Álvarez, Marta; Troupin, Charles

doi:10.1016/j.dsr.2013.07.004

Cited by 16 publications

(32 citation statements)

References 73 publications

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“…In the present study, the highest rate of NH + 4 regeneration was measured at T 0 , coinciding with the highest ambient ammonium concentration and abundance of phytoplankton, notably flagellates. This offered circumstantial evidence supporting a role for microflagellates in NH + 4 regeneration (Benavides et al, 2013 recycling that was sufficient to meet phytoplankton requirements, as also reported for other upwelling systems (Benavides et al, 2013(Benavides et al, , 2014Raimbault and Garcia, 2008;Clark et al, 2011;Fernández and Farías, 2012).…”

Section: The Regeneration Of Inorganic Nitrogenmentioning

confidence: 63%

“…There are relatively few studies of nitrogen assimilation in the north-west African region against which to draw comparisons; NO − 3 assimilation measured within the photic zone was previously reported in the range < 0.2-31 nmol L −1 h −1 (Varela et al, 2005;Dugdale et al, 1990), while NH + 4 assimilation was reported in the range < 0.2-105 nmol L −1 h −1 (Varela et al, 2005;Benavides et al, 2013). The fact that rates of NH + 4 and NO − 3 assimilation were broadly similar for P 1 despite the difference in nitrogen source availability was perhaps the most striking observation.…”

Section: R Clark Et Al: the Significance Of Nitrogen Regeneratiomentioning

confidence: 99%

“…We are unaware of previous studies for the Mauritanian system with which to compare this data. For Cape Ghir (north of the study location), Benavides et al (2013) reported NH + 4 regeneration rates of 8 nmol L −1 h −1 . For the Benguela system Probyn (1987Probyn ( , 1990 reported rates of 0-125 nmol L −1 h −1 and Benavides et al (2014) reported rates of 90-130 nmol L −1 h −1 .…”

Section: The Regeneration Of Inorganic Nitrogenmentioning

confidence: 99%

“…For the less productive Iberian upwelling system, rates of 0.09-2.52 nmol L −1 h −1 have been reported . Benavides et al (2013) speculated in their study of the Benguela system that high rates of NH + 4 regeneration were driven by a high abundance of dinoflagellates and mixotrophic microflagellates. In the present study, the highest rate of NH + 4 regeneration was measured at T 0 , coinciding with the highest ambient ammonium concentration and abundance of phytoplankton, notably flagellates.…”

Section: The Regeneration Of Inorganic Nitrogenmentioning

confidence: 99%

“…Nutrient regeneration is a product of heterotrophic dissolved organic matter (DOM) degradation by microplankton (bacteria, flagellates, ciliates), following its release from phytoplankton due to grazing (Probyn, 1987;Varela et al, 2003;Bode et al, 2004) or its active release from phytoplankton during nutrient assimilation (Bronk et al, 1994;Raimbault and Garcia, 2008;Benavides et al, 2013). Alternative routes of NH + 4 regeneration in upwelling systems may be minor (e.g.…”

Section: The Regeneration Of Inorganic Nitrogenmentioning

confidence: 99%

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The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

2016

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Abstract. The Lagrangian progression of a biological community was followed in a filament of the Mauritanian upwelling system, north-west Africa, during offshore advection. The inert dual tracers sulfur hexafluoride and helium-3 labelled a freshly upwelled patch of water that was mapped for 8 days. Changes in biological, physical, and chemical characteristics were measured, including phytoplankton productivity, nitrogen assimilation, and regeneration. Freshly upwelled water contained high nutrient concentrations but was depleted in N compared to Redfield stoichiometry. The highest rate of primary productivity was measured on the continental shelf, associated with high rates of nitrogen assimilation and a phytoplankton community dominated by diatoms and flagellates. Indicators of phytoplankton abundance and activity decreased as the labelled water mass transited the continental shelf slope into deeper water, possibly linked to the mixed layer depth exceeding the light penetration depth. By the end of the study, the primary productivity rate decreased and was associated with lower rates of nitrogen assimilation and lower nutrient concentrations. Nitrogen regeneration and assimilation took place simultaneously. Results highlighted the importance of regenerated NH + 4 in sustaining phytoplankton productivity and indicate that the upwelled NO − 3 pool contained an increasing fraction of regenerated NO − 3 as it advected offshore. By calculating this fraction and incorporating it into an f ratio formulation, we estimated that of the 12.38 Tg C of annual regional production, 4.73 Tg C was exportable.

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Section: The Regeneration Of Inorganic Nitrogenmentioning

confidence: 63%

Section: R Clark Et Al: the Significance Of Nitrogen Regeneratiomentioning

confidence: 99%

Section: The Regeneration Of Inorganic Nitrogenmentioning

confidence: 99%

Section: The Regeneration Of Inorganic Nitrogenmentioning

confidence: 99%

Section: The Regeneration Of Inorganic Nitrogenmentioning

confidence: 99%

See 3 more Smart Citations

The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

2016

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Nitrogen fixation in the eastern Atlantic reaches similar levels in the Southern and Northern Hemisphere

et al. 2017

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Euphotic layer dinitrogen (N2) fixation and primary production (PP) were measured in the eastern Atlantic Ocean (38°N–21°S) using 15N2 and 13C bicarbonate tracer incubations. This region is influenced by Saharan dust deposition and waters with low nitrogen to phosphorus (N/P) ratios originating from the Subantarctic and the Benguela upwelling system. Depth‐integrated rates of N2 fixation in the north (0°N–38°N) ranged from 59 to 370 µmol N m−2 d−1, with the maximal value at 19°N under the influence of the northwest African upwelling. Diazotrophic activity in the south (0°S–21°S), though slightly lower, was surprisingly close to observations in the north, with values ranging from 47 to 119 µmol N m−2 d−1. Our North Atlantic N2 fixation rates correlate well with dust deposition, while those in the South Atlantic correlate strongly with excess phosphate relative to nitrate. There, the necessary iron is assumed to be supplied from the Benguela upwelling system. When converting N2 fixation to carbon uptake using a Redfield ratio (6.6), we find that N2 fixation may support up to 9% of PP in the subtropical North Atlantic (20°N–38°N), 5% in the tropical North Atlantic (0°N–20°N), and 1% of PP in the South Atlantic (0°S–21°S). Combining our data with published data sets, we estimate an annual N input of 27.6 ± 10 Tg N yr−1 over the open Atlantic Ocean, 11% of which enters the region between 20°N and 50°N, 71% between 20°N and 10°S, and 18% between 10°N and 45°S.

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High‐nitrogen fixation rates in the particulate and dissolved pools in the Western Tropical Pacific (Solomon and Bismarck Seas)

Berthelot

Benavides

Moisander

et al. 2017

Geophysical Research Letters

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Dinitrogen (N2) fixation rates were investigated in the euphotic layer of the Bismarck and Solomon Seas using 15N2 incubation assays taking into account both the particulate and the dissolved pools. Average depth‐integrated particulate N2 fixation rates were 203 (range 43–399) and 1396 (range 176–3132) μmol N m−2 d−1 in the Bismarck and Solomon Seas, respectively. In both seas, N2 fixation measured in the dissolved pool was similar to particulate N2 fixation, highlighting the potentially substantial underestimation of N2 fixation in oceanic budgets when only particulate N2 fixation is considered. Among the diazotroph phylotypes targeted using quantitative polymerase chain reaction amplification of nifH genes, Trichodesmium was the most abundant. Regression analyses suggest that it accounted for the major proportion of N2 fixation. However, unicellular cyanobacterial and non‐cyanobacterial diazotrophs were also occasionally abundant. This study reports high pelagic N2 fixation rates and confirms that the Western Tropical South Pacific is a hot spot for marine N2 fixation.

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Low contribution of N2 fixation to new production and excess nitrogen in the subtropical northeast Atlantic margin

Cited by 16 publications

References 73 publications

The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

Nitrogen fixation in the eastern Atlantic reaches similar levels in the Southern and Northern Hemisphere

High‐nitrogen fixation rates in the particulate and dissolved pools in the Western Tropical Pacific (Solomon and Bismarck Seas)

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