On the Nitrous Oxide Accumulation in Intermediate Waters of the Eastern South Pacific Ocean

Carrasco, Cristina; Karstensen, Johannes

doi:10.3389/fmars.2017.00024

Cited by 18 publications

(21 citation statements)

References 65 publications

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“…Downward mixing and diffusion from ODZ is unlikely because the ETSP is a major upwelling region and ODZ samples had high SP values (see next paragraph). We conclude that localized N2O production from nitrification and denitrification are important pathways in this region of the water column, and probably contributed to N2O concentrations maxima in intermediate waters, as reported by Carrasco et al (2017).…”

Section: N2o Cycling Pathways Inferred From Natural Abundance Isotopic and Isotopomeric Signaturessupporting

confidence: 80%

Investigating the effect of El Niño on nitrous oxide distribution in the Eastern Tropical South Pacific

Ji¹,

Altabet²,

Bange³

et al. 2018

Preprint

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Abstract. The open ocean is a major source of atmospheric warming and ozone depleting gas nitrous oxide (N2O). Intense sea-to-air fluxes of N2O occur in major oceanic upwelling regions such as the Eastern Tropical South Pacific Ocean (ETSP). The ETSP is influenced by the El Ni&#241;o-Southern Oscillation that leads to inter-annual variations of physical, chemical and biological properties. A strong El Ni&#241;o was developing in this region in October 2015, during which we investigated the N2O production pathways and, by comparing to previous non-El Ni&#241;o years, the effects of El Ni&#241;o on water column N2O distributions and fluxes. Analysis of N2O natural abundance isotopomers suggested that both nitrification and partial denitrification (nitrate and nitrite reduction to N2O) were important N2O production pathways. Higher than normal sea-surface temperatures were associated with a deepening of the oxycline, while the level of sea surface N2O supersaturation on the continental shelf was nearly an order of magnitude lower than those of non-El Ni&#241;o years. Therefore, a significant reduction of N2O efflux in the ETSP occurred during the 2015 El Ni&#241;o event. At both offshore and coastal stations, the N2O concentration profiles during El Ni&#241;o showed moderate N2O concentration gradients, and peak N2O concentrations were deeper than during non-El Ni&#241;o years; this was likely the result of suppressed upwelling retaining N2O in subsurface waters. The depth-integrated N2O concentrations during El Ni&#241;o were nearly twice as high as those measured in non-El Ni&#241;o years, indicating subsurface N2O during El Ni&#241;o could be a reservoir for intense N2O effluxes when normal upwelling is resumed after El Ni&#241;o.

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Section: N2o Cycling Pathways Inferred From Natural Abundance Isotopic and Isotopomeric Signaturessupporting

confidence: 80%

Investigating the effect of El Niño on nitrous oxide distribution in the Eastern Tropical South Pacific

Ji¹,

Altabet²,

Bange³

et al. 2018

Preprint

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“…Carrasco et al. (2017) interpret the gradual accumulation of N 2 O in AAIW between 60°S and 20°S as production predominantly from nitrification, based on the positive correlation with apparent N 2 O production and AOU. This interpretation concurs with isotopic analyses suggesting that N 2 O accumulation in aerobic intermediate waters results from nitrification by ammonia‐oxidizing archaea (Toyoda et al., 2019).…”

Section: Discussionmentioning

confidence: 99%

Quantifying Nitrous Oxide Cycling Regimes in the Eastern Tropical North Pacific Ocean With Isotopomer Analysis

Kelly

Travis

Baya

et al. 2021

Global Biogeochemical Cycles

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Nitrous oxide (N2O), a potent greenhouse gas, is produced disproportionately in marine oxygen deficient zones (ODZs). To quantify spatiotemporal variation in N2O cycling in an ODZ, we analyzed N2O concentration and isotopologues along a transect through the eastern tropical North Pacific (ETNP). At several stations along this transect, N2O concentrations reached a near surface maximum that exceeded prior measurements in this region, of up to 226.1 ± 20.5 nM at the coast. Above the σθ = 25.0 kg/m3 isopycnal, Keeling plot analysis revealed two sources to the near‐surface N2O maximum, with different δ15N2Oα and δ15N2Oβ values, but each with a site preference (SP) of 6‰–8‰. Given expected SPs for nitrification and denitrification, each of these sources could be comprised of 17%–26% nitrification (bacterial or archeal), and 74%–83% denitrification (or nitrifier‐denitrification). Below the σθ = 25.0 kg/m3 isopycnal, box model analysis indicated that the observed 46‰–50‰ SPs in the anoxic core of the ODZ cannot be reproduced in a steady state context without an SP for N2O production by denitrification, and may indicate instead a transient net consumption of N2O. Furthermore, time‐dependent model results indicated that while δ15N2Oα and δ18O‐N2O reflect both N2O production and consumption in the anoxic core of the ODZ, δ15N2Oβ predominantly reflects N2O sources. Finally, we infer that the high (N2O) observed at some stations derive from a set of conditions supporting high rates of N2O production that have not been previously encountered in this region.

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“…Recent studies contrast the view of nitrification vs. denitrification as the main N 2 O source in ODZs (Nicholls et al, 2007;Babbin et al, 2015;Ji et al, 2015b;Yang et al, 2017). They show the importance of denitrification in N 2 O production in the ETNP from model outputs (Babbin et al, 2015) and in the ETSP from tracer incubation experiments (Dalsgaard et al, 2012;Ji et al, 2015b), based on natural abundance isotopes in N 2 O (Casciotti et al, 2018) or from water mass analysis of apparent N 2 O production ( N 2 O) and apparent O 2 utilization (AOU) (Carrasco et al, 2017). 45,46 N 2 O production from the addition of 15 N-labeled NH + 4 , NO − 2 and/or NO − 3 revealed nitrification as a source of N 2 O within the oxic-anoxic interface, but overall denitrification dominated N 2 O production with higher rates at the interface and in anoxic waters (Ji et al, 2015b(Ji et al, , 2018a.…”

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confidence: 99%

Regulation of nitrous oxide production in low-oxygen waters off the coast of Peru

et al. 2020

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Abstract. Oxygen-deficient zones (ODZs) are major sites of net natural nitrous oxide (N2O) production and emissions. In order to understand changes in the magnitude of N2O production in response to global change, knowledge on the individual contributions of the major microbial pathways (nitrification and denitrification) to N2O production and their regulation is needed. In the ODZ in the coastal area off Peru, the sensitivity of N2O production to oxygen and organic matter was investigated using 15N tracer experiments in combination with quantitative PCR (qPCR) and microarray analysis of total and active functional genes targeting archaeal amoA and nirS as marker genes for nitrification and denitrification, respectively. Denitrification was responsible for the highest N2O production with a mean of 8.7 nmol L−1 d−1 but up to 118±27.8 nmol L−1 d−1 just below the oxic–anoxic interface. The highest N2O production from ammonium oxidation (AO) of 0.16±0.003 nmol L−1 d−1 occurred in the upper oxycline at O2 concentrations of 10–30 µmol L−1 which coincided with the highest archaeal amoA transcripts/genes. Hybrid N2O formation (i.e., N2O with one N atom from NH4+ and the other from other substrates such as NO2-) was the dominant species, comprising 70 %–85 % of total produced N2O from NH4+, regardless of the ammonium oxidation rate or O2 concentrations. Oxygen responses of N2O production varied with substrate, but production and yields were generally highest below 10 µmol L−1 O2. Particulate organic matter additions increased N2O production by denitrification up to 5-fold, suggesting increased N2O production during times of high particulate organic matter export. High N2O yields of 2.1 % from AO were measured, but the overall contribution by AO to N2O production was still an order of magnitude lower than that of denitrification. Hence, these findings show that denitrification is the most important N2O production process in low-oxygen conditions fueled by organic carbon supply, which implies a positive feedback of the total oceanic N2O sources in response to increasing oceanic deoxygenation.

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On the Nitrous Oxide Accumulation in Intermediate Waters of the Eastern South Pacific Ocean

Cited by 18 publications

References 65 publications

Investigating the effect of El Niño on nitrous oxide distribution in the Eastern Tropical South Pacific

Investigating the effect of El Niño on nitrous oxide distribution in the Eastern Tropical South Pacific

Quantifying Nitrous Oxide Cycling Regimes in the Eastern Tropical North Pacific Ocean With Isotopomer Analysis

Regulation of nitrous oxide production in low-oxygen waters off the coast of Peru

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