‘NO’, a useful tool for the estimation of nitrate deficits in the Arabian Sea

Naqvi, S.W.A.; Gupta, R. Sen

doi:10.1016/0198-0149(85)90071-8

Cited by 43 publications

(26 citation statements)

References 16 publications

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“…N from M90 was significantly higher than most estimates available for a similar OMZ in the Arabian Sea (Naqvi and Gupta, 1985;Howell et al, 1997;Bange et al, 2000), and it was only comparable with values up to 7.3 mol m −2 found by Naqvi and Gupta (1985) ever, markedly lower than both N from M90 and N from previous work in the OMZ of the Arabian Sea (minimum N = 1.0 mol m −2 ; Bange et al, 2000). This suggests not only strong denitrification activities within mesoscale eddies formed off the Peruvian coast but also high short-term variability as they move offshore.…”

Section: Changes In N Cyclingmentioning

confidence: 87%

“…In order to provide a quantitative estimate of the amount of denitrification that took place in eddy A, as well as to assess how it changed between the two surveys, in this section we present estimates of nitrate deficit ( N) by means of the "NO" approach (Naqvi and Gupta, 1985). "NO" is used as a quasi-conservative water mass tracer (Broecker, 1974) (Bange et al, 2000).…”

Section: Changes In N Cyclingmentioning

confidence: 99%

“…Hence, the obtained regression lines ("NO" M90 , "NO" M91 , Fig. 7) represent conditions which are expected when the OMZ is not affected by denitrification (Naqvi and Gupta, 1985). We calculated N by using "NO" M90 and "NO" M91 according to the following expression (Bange et al, 2000):…”

Section: Changes In N Cyclingmentioning

confidence: 99%

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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: Changes In N Cyclingmentioning

confidence: 87%

Section: Changes In N Cyclingmentioning

confidence: 99%

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

et al. 2016

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“…Cline and Richards, 1972;Codispoti and Richards, 1976), the ETSP (e.g. Codispoti and Packard, 1980), and the Arabian Sea (Bange et al, 2000;Mantoura et al, 1993;Naqvi, 1987;Naqvi and Sen-Gupta, 1985). Smaller, and more transient sites occur near the boundaries of the three major identified sites (e.g.…”

Section: The Denitrification Sinkmentioning

confidence: 99%

The oceanic fixed nitrogen and nitrous oxide budgets: Moving targets as we enter the anthropocene?

Codispoti¹,

Brandes²,

Christensen³

et al. 2001

Sci. Mar.

760

695

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SUMMARY: New data force us to raise previous estimates of oceanic denitrification. Our revised estimate of ~ 450 Tg N yr -1 (Tg = 10 12 g) produces an oceanic fixed N budget with a large deficit ) that can be explained only by positing an ocean that has deviated far from a steady-state, the need for a major upwards revision of fixed N inputs, particularly nitrogen fixation, or both. Oceanic denitrification can be significantly altered by small re-distributions of carbon and dissolved oxygen. Since fixed N is a limiting nutrient, uncompensated changes in denitrification affect the ocean's ability to sequester atmospheric CO 2 via the "biological pump". We have also had to modify our concepts of the oceanic N 2 O regime to take better account of the extremely high N 2 O saturations that can arise in productive, low oxygen waters. Recent results from the western Indian Shelf during a period when hypoxic, suboxic and anoxic waters were present produced a maximum surface N 2 O saturation of > 8000%, a likely consequence of "stop and go" denitrification. The sensitivity of N 2 O production and consumption to small changes in the oceanic dissolved oxygen distribution and to the "spin-up" phase of denitrification suggests that the oceanic source term for N 2 O could change rapidly.

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“…Broecker (1974) and then Naqvi and Sen Gupta (1985) used the NO tracer to estimate the NO3 -deficiency observed in the Arabian Sea. Michaels et al (1996) and Gruber and Sarmiento (1997) proposed the N* as a tracer to determine the proportion of changes in the fixed 60 nitrogen stock (all nitrogenous forms except atmospheric N2) resulting from the combined effect of denitrification and/or of diazotrophy.…”

mentioning

confidence: 99%

Excess nitrogen as a marker of intense dinitrogen fixation in the Western Tropical South Pacific Ocean: impact on the thermocline waters of the South Pacific

Fumenia

Moutin

Bonnet

et al. 2018

Preprint

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Abstract. As part of the Oligotrophy to UlTra-oligotrophy PACific Experiment cruise, which took place in the Western 15Tropical South Pacific during the austral summer (March-April 2015), we present data on nitrate, phosphate and on particulate and dissolved organic matter. The stoichiometric nitrogen-to-phosphorus ratios of the inorganic and organic material and the tracer N* are described. N* allows to trace changes in the proportion of fixed nitrogen due to diazotrophy and/or denitrification.Our results showed that the Melanesian archipelago waters between 160° E and 170° W are characterized by a deficit of nitrate and phosphate in the productive layer, significant dinitrogen fixation rates and an excess of particulate organic nitrogen 20 compared to the canonical ratio of Redfield. A positive N* anomaly was observed in the productive layer reflecting the combined effect of phosphate uptake by diazotrophic organisms and remineralization of excess particulate organic nitrogen.The South Pacific Gyre waters between 170° W and 160° W were depleted in nitrate but rich in phosphate. Surface waters exhibited very low dinitrogen fixation rates, an absence of excess particulate organic nitrogen and a N* signal close to zero.The higher iron availability coupled with an absence of nitrate in the suface water of the Melanesian archipelago could 25 stimulate the diazotrophic activity, which in turn will introduce excess nitrogen, deplete the surface waters in phosphate and be the explanation for the positive N* anomaly in the Melanesian archipelago waters. In the thermocline waters, the N* tracer revealed its full complexity, with notably the cumulative effect of the remineralization of particulate organic nitrogen and the

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‘NO’, a useful tool for the estimation of nitrate deficits in the Arabian Sea

Cited by 43 publications

References 16 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

The oceanic fixed nitrogen and nitrous oxide budgets: Moving targets as we enter the anthropocene?

Excess nitrogen as a marker of intense dinitrogen fixation in the Western Tropical South Pacific Ocean: impact on the thermocline waters of the South Pacific

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