Nitrous oxide production by nitrification and denitrification in the Eastern Tropical South Pacific oxygen minimum zone

Ji, Qixing; Babbin, Andrew R.; Jayakumar, Amal; Oleynik, Sergey; Ward, Bess B.

doi:10.1002/2015gl066853

Cited by 122 publications

(211 citation statements)

References 71 publications

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“…3). Such a pattern has been previously reported for the ETSP (Farías et al, 2007) and similar systems with prominent OMZs (Bange et al, 2001;Bange et al, 2010), and it is generally ascribed to alternating activity of microbial N 2 O production-consumption pathways along the vertical O 2 gradients (Codispoti and Christensen, 1985;Ji et al, 2015). …”

Section: Depth Distribution Of N 2 Omentioning

confidence: 76%

Influence of mesoscale eddies on the distribution of nitrous oxide in the eastern tropical South Pacific

et al. 2016

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Abstract. Recent observations in the eastern tropical South Pacific (ETSP) have shown the key role of meso-and submesoscale processes (e.g. eddies) in shaping its hydrographic and biogeochemical properties. Off Peru, elevated primary production from coastal upwelling in combination with sluggish ventilation of subsurface waters fuels a prominent oxygen minimum zone (OMZ). Given that nitrous oxide (N 2 O) production-consumption processes in the water column are sensitive to oxygen (O 2 ) concentrations, the ETSP is a region of particular interest to investigate its source-sink dynamics. To date, no detailed surveys linking mesoscale processes and N 2 O distributions as well as their relevance to nitrogen (N) cycling are available. In this study, we present the first measurements of N 2 O across three mesoscale eddies (two mode water or anticyclonic and one cyclonic) which were identified, tracked, and sampled during two surveys carried out in the ETSP in November-December 2012. A two-peak structure was observed for N 2 O, wherein the two maxima coincide with the upper and lower boundaries of the OMZ, indicating active nitrification and partial denitrification. This was further supported by the abundances of the key gene for nitrification, ammonium monooxygenase (amoA), and the gene marker for N 2 O production during denitrification, nitrite reductase (nirS). Conversely, we found strong N 2 O depletion in the core of the OMZ (O 2 < 5 µmol L −1 ) to be consistent with nitrite (NO − 2 ) accumulation and low levels of nitrate (NO − 3 ), thus suggesting active denitrification. N 2 O depletion within the OMZ's core was substantially higher in the centre of mode water eddies, supporting the view that eddy activity enhances N-loss processes off Peru, in particular near the shelf break where nutrient-rich, productive waters from upwelling are trapped before being transported offshore. Analysis of eddies during their propagation towards the open ocean showed that, in general, "ageing" of mesoscale eddies tends to decrease N 2 O concentrations through the water column in response to the reduced supply of material to fuel N loss, although hydrographic variability might also significantly impact the pace of the production-consumption pathways for N 2 O. Our results evidence the relevance of mode water eddies for N 2 O distribution, thereby improving our understanding of the N-cycling processes, which are of crucial importance in times of climate change and ocean deoxygenation.

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Section: Depth Distribution Of N 2 Omentioning

confidence: 76%

Influence of mesoscale eddies on the distribution of nitrous oxide in the eastern tropical South Pacific

et al. 2016

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“…Farías et al, 2009;Ji et al, 2015). During denitrification, the canonical reduction of nitrate to molecular nitrogen, N 2 O evolves as an intermediate product.…”

Section: Introductionmentioning

confidence: 99%

“…There is a strong indication that at low oxygen concentrations nitrification and denitrification may take place in close proximity (Kalvelage et al, 2011), and the N 2 O production and consumption under these conditions are strongly influenced by the interaction of both processes (Ji et al, 2015). Measurements of N 2 O consumption rates in the eastern tropical North Pacific Ocean (ETNP) furthermore provided evidence for a rapid N 2 O cycling, although depth profiles of N 2 O seemed to be relatively invariant over time .…”

Section: Introductionmentioning

confidence: 99%

Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru

et al. 2016

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Abstract. Depth profiles of nitrous oxide (N 2 O) were measured during six cruises to the upwelling area and oxygen minimum zone (OMZ) off Peru in 2009 and 2012/2013, covering both the coastal shelf region and the adjacent open ocean. N 2 O profiles displayed a strong sensitivity towards oxygen concentrations. Open ocean profiles with distances to the shelf break larger than the first baroclinic Rossby radius of deformation showed a transition from a broad maximum close to the Equator to a double-peak structure south of 5 • S where the oxygen minimum was more pronounced. Maximum N 2 O concentrations in the open ocean were about 80 nM. A linear relationship between N 2 O and apparent oxygen utilization (AOU) could be found for measurements within the upper oxycline, with a slope similar to studies in other oceanic regions. In contrast, N 2 O profiles close to the shelf revealed a much higher variability, and N 2 O concentrations higher than 100 nM were often observed. The highest N 2 O concentration measured at the shelf was ∼ 850 nM. Due to the extremely sharp oxygen gradients at the shelf, N 2 O maxima occurred in very shallow water depths of less than 50 m. In the coastal area, a linear relationship between N 2 O and AOU could not be observed as extremely high N 2 O values were scattered over the full range of oxygen concentrations. The data points that showed the strongest deviation from a linear N 2 O / AOU relationship also showed signals of intense nitrogen loss. These results indicate that the coastal upwelling at the Peruvian coast and the subsequent strong remineralization in the water column causes conditions that lead to extreme N 2 O accumulation, most likely due to the interplay of intense mixing and high rates of remineralization which lead to a rapid switching of the OMZ waters between anoxic and oxic conditions. This, in turn, could trigger incomplete denitrification or pulses of increased nitrification with extreme N 2 O production.

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“…N 2 O production is highest under nearly anoxic conditions, where oxygen concentrations restrain both nitrification (too little oxygen) and denitrification (too much oxygen). Both processes produce N 2 O, with a higher N 2 O yield in oxygen stress (Goreau et al, 1980;Patureau et al, 1994;Ji et al, 2015). In addition, when nitrifying microbes become oxygen limited, they too start to reduce NO − 2 to N 2 O (Poth and Focht, 1985;Wilson et al, 2014).…”

Section: N 2 O Dynamics In the Egbmentioning

confidence: 99%

“…The main biological pathways of N 2 O production are highly dependent on the oxygen conditions and the availability of organic matter, nitrite (NO − 2 ) and nitrate (Ward, 2013;Murray et al, 2015). In seas, nitrification has been considered the primary pathway of N 2 O production (Freing et al, 2012), but recent studies have suggested that the role of incomplete denitrification in the oceanic oxygen minimum zones might have been previously underestimated Ji et al, 2015). Furthermore, it has been shown that archaeal nitrification dominates oceanic N 2 O production and that this is much more sensitive to oxygen concentrations than bacterial nitrication (Löscher et al, 2012;Freing et al, 2012).…”

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confidence: 99%

Effects of the 2014 major Baltic inflow on methane and nitrous oxide dynamics in the water column of the central Baltic Sea

et al. 2017

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Abstract. In late 2014, a large, oxygen-rich salt water inflow entered the Baltic Sea and caused considerable changes in deep water oxygen concentrations. We studied the effects of the inflow on the concentration patterns of two greenhouse gases, methane and nitrous oxide, during the following year (2015) in the water column of the Gotland Basin. In the eastern basin, methane which had previously accumulated in the deep waters was largely removed during the year. Here, volume-weighted mean concentration below 70 m decreased from 108 nM in March to 16.3 nM over a period of 141 days (0.65 nM d −1 ), predominantly due to oxidation (up to 79 %) following turbulent mixing with the oxygen-rich inflow. In contrast nitrous oxide, which was previously absent from deep waters, accumulated in deep waters due to enhanced nitrification following the inflow. Volume-weighted mean concentration of nitrous oxide below 70 m increased from 11.8 nM in March to 24.4 nM in 141 days (0.09 nM d −1 ). A transient extreme accumulation of nitrous oxide (877 nM) was observed in the deep waters of the Eastern Gotland Basin towards the end of 2015, when deep waters turned anoxic again, sedimentary denitrification was induced and methane was reintroduced to the bottom waters. The Western Gotland Basin gas biogeochemistry was not affected by the inflow.

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Nitrous oxide production by nitrification and denitrification in the Eastern Tropical South Pacific oxygen minimum zone

Cited by 122 publications

References 71 publications

Influence of mesoscale eddies on the distribution of nitrous oxide in the eastern tropical South Pacific

Influence of mesoscale eddies on the distribution of nitrous oxide in the eastern tropical South Pacific

Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru

Effects of the 2014 major Baltic inflow on methane and nitrous oxide dynamics in the water column of the central Baltic Sea

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Nitrous oxide production by nitrification and denitrification in the Eastern Tropical South Pacific oxygen minimum zone

Cited by 122 publications

References 71 publications

Influence of mesoscale eddies on the distribution of nitrous oxide in the eastern tropical South Pacific

Influence of mesoscale eddies on the distribution of nitrous oxide in the eastern tropical South Pacific

Extreme N&lt;sub&gt;2&lt;/sub&gt;O accumulation in the coastal oxygen minimum zone off Peru

Effects of the 2014 major Baltic inflow on methane and nitrous oxide dynamics in the water column of the central Baltic Sea

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Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru