Nitrate isotopic composition between Bermuda and Puerto Rico: Implications for N2 fixation in the Atlantic Ocean

Knapp, Angela N.; DiFiore, Peter J.; Deutsch, Curtis; Sigman, Daniel M.; Lipschultz, Fredric

doi:10.1029/2007gb003107

Cited by 127 publications

(215 citation statements)

References 73 publications

(172 reference statements)

Supporting

Mentioning

194

Contrasting

Order By: Relevance

“…3a). Atmospheric deposition, which is not accounted for in the model, may play an important role in determining the shallow nitrate δ 15 NO 3 in the Atlantic (Knapp et al, 2008). Deep ocean values in the Atlantic are slightly lower than observed, but the observations lie within the envelope of model uncertainty.…”

Section: Model-data Comparisonmentioning

confidence: 82%

Marine denitrification rates determined from a global 3-D inverse model

et al. 2013

View full text Add to dashboard Cite

A major impediment to understanding long-term changes in the marine nitrogen (N) cycle is the persistent uncertainty about the rates, distribution, and sensitivity of its largest fluxes in the modern ocean. We use a global ocean circulation model to obtain the first 3-D estimate of marine denitrification rates that is maximally consistent with available observations of nitrate deficits and the nitrogen isotopic ratio of oceanic nitrate. We find a global rate of marine denitrification in suboxic waters and sediments of 120–240 Tg N yr⁻¹, which is lower than many other recent estimates. The difference stems from the ability to represent the 3-D spatial structure of suboxic zones, where denitrification rates of 50–77 Tg N yr⁻¹ result in up to 50% depletion of nitrate. This depletion reduces the effect of local isotopic enrichment on the rest of the ocean, allowing the N isotope ratio of oceanic nitrate to be achieved with a sedimentary denitrification rate about 1.3–2.3 times that of suboxic zones. This balance of N losses between sediments and suboxic zones is shown to obey a simple relationship between isotope fractionation and the degree of nitrate consumption in the core of the suboxic zones. The global denitrification rates derived here suggest that the marine nitrogen budget is likely close to balanced

show abstract

Section: Model-data Comparisonmentioning

confidence: 82%

Marine denitrification rates determined from a global 3-D inverse model

et al. 2013

View full text Add to dashboard Cite

show abstract

“…Low δ 15 N signatures of particles from sediment traps in the tropical North Pacific (Karl et al, 1997Scharek et al, 1999a, b) and Atlantic (Altabet, 1988;Bourbonnais et al, 2009;Knapp et al, 2005;Mahaffey et al, 2003) suggest that at least part of the recently fixed N is ultimately exported out of the photic zone. Knapp et al (2008) and Bourbonnais et al (2009) also observed a low δ 15 N of NO − 3 (relative to δ 18 O-NO − 3 ) in surface waters in the western and eastern subtropical Atlantic Ocean, supporting the role of N 2 fixers in these regions. Böttjer et al (2017) revealed that N 2 fixation supports 26-47 % of particulate N (PN) export over a 9-year time series (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) period at station ALOHA (North Pacific Subtropical Gyre).…”

Section: Introductionmentioning

confidence: 88%

N2 fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)

et al. 2018

View full text Add to dashboard Cite

Abstract. We performed nitrogen (N) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (FebruaryMarch 2015). Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) station, allowing us to consider only vertical exchanges for the budgets. We quantified all major vertical N fluxes both entering (N 2 fixation, nitrate turbulent diffusion, atmospheric deposition) and leaving the photic layer (particulate N export). The three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic Melanesian archipelago (MA, stations LD A and LD B) than in the ultra-oligotrophic waters of the South Pacific Gyre (SPG, station LD C). N 2 fixation rates were extremely high at both LD A (593 ± 51 µmol N m −2 d −1 ) and LD B (706 ± 302 µmol N m −2 d −1 ), and the diazotroph community was dominated by Trichodesmium. N 2 fixation rates were lower (59 ± 16 µmol N m −2 d −1 ) at LD C, and the diazotroph community was dominated by unicellular N 2 -fixing cyanobacteria (UCYN). At all stations, N 2 fixation was the major source of new N (> 90 %) before atmospheric deposition and upward nitrate fluxes induced by turbulence. N 2 fixation contributed circa 13-18 % of primary production in the MA region and 3 % in the SPG water and sustained nearly all new primary production at all stations. The e ratio (e ratio = particulate carbon export / primary production) was maximum at LD A (9.7 %) and was higher than the e ratio in most studied oligotrophic regions (< 5 %), indicating a high efficiency of the WTSP to export carbon relative to primary production. The direct export of diazotrophs assessed by qPCR of the nifH gene in sediment traps represented up to 30.6 % of the PC export at LD A, while their contribution was 5 and < 0.1 % at LD B and LD C, respectively. At the three studied stations, the sum of all N input to the photic layer exceeded the N output through organic matter export. This disequilibrium leading to N accumulation in the upper Published by Copernicus Publications on behalf of the European Geosciences Union.

show abstract

“…It does not include any new production due to nitrogen fixation, zooplankton migration, or atmospheric deposition of nitrate. At BATS, nitrogen fixation has been estimated to be 0.03 to 0.08 mol N m −2 yr −1 (Singh et al, 2013;Knapp et al, 2008), which is equivalent to 5 to 12 % of the new production we report from the flux gauge method. Zooplankton migration from 2003 to 2006 has been estimated to support a new production of 2 g C m −2 yr −1 (Steinberg et al, 2012), which is equivalent to 0.025 mol N m −2 yr −1 using the revised Redfield ratios of Anderson and Sarmiento (1994) and thus is only 4 % of the new production rate estimated by the flux gauge technique.…”

Section: The Fluxes Of Helium-3 and Nitratementioning

confidence: 99%

“…Net community production has been estimated from the seasonal accumulation of O 2 / Ar (Spitzer and Jenkins, 1989) and the drawdown of dissolved inorganic carbon (Gruber et al, 1998;Brix et al, 2006;Fernandez-Castro et al, 2012). New production has been estimated from bottle incubations (Lipschultz, 2001;Lipschultz et al, 2002) and has also been studied using nitrogen isotopes (Fawcett et al, 2014;Knapp et al, 2008).…”

Section: Data Collectionmentioning

confidence: 99%

The 3He flux gauge in the Sargasso Sea: a determination of physical nutrient fluxes to the euphotic zone at the Bermuda Atlantic Time-series Site

et al. 2015

View full text Add to dashboard Cite

Abstract. Significant rates of primary production occur in the oligotrophic ocean, without any measurable nutrients present in the mixed layer, fueling a scientific paradox that has lasted for decades. Here, we provide a new determination of the annual mean physical supply of nitrate to the euphotic zone in the western subtropical North Atlantic. We combine a 3-year time series of measurements of tritiugenic 3 He from 2003 to 2006 in the surface ocean at the Bermuda Atlantic Time-series Study (BATS) site with a sophisticated noble gas calibrated air-sea gas exchange model to constrain the 3 He flux across the sea-air interface, which must closely mirror the upward 3 He flux into the euphotic zone. The product of the 3 He flux and the observed subsurface nitrate-3 He relationship provides an estimate of the minimum rate of new production in the BATS region. We also apply the gas model to an earlier time series of 3 He measurements at BATS in order to recalculate new production fluxes for the 1985 to 1988 time period. The observations, despite an almost 3-fold difference in the nitrate-3 He relationship, yield a roughly consistent estimate of nitrate flux. In particular, the nitrate flux from 2003 to 2006 is estimated to be 0.65 ± 0.14 mol m −2 yr −1 , which is ∼ 40 % smaller than the calculated flux for the period from 1985 to 1988. The difference in nitrate flux between the time periods may be signifying a real difference in new production resulting from changes in subtropical mode water formation. Overall, the nitrate flux is larger than most estimates of export fluxes or net community production fluxes made locally for the BATS site, which is likely a reflection of the larger spatial scale covered by the 3 He technique and potentially also by the decoupling of 3 He and nitrate during the obduction of water masses from the main thermocline into the upper ocean. The upward nitrate flux is certainly large enough to support observed rates of primary production at BATS and more generally in the oligotrophic subtropical ocean.

show abstract

Nitrate isotopic composition between Bermuda and Puerto Rico: Implications for N₂ fixation in the Atlantic Ocean

Abstract: . One important caveat is that fixed N in atmospheric deposition may contribute a significant proportion of the low-d 15 N N in the Sargasso Sea thermocline, in which case the relatively low rate we estimate for N 2 fixation would still be too high.

Cited by 127 publications

References 73 publications

Marine denitrification rates determined from a global 3-D inverse model

Marine denitrification rates determined from a global 3-D inverse model

N<sub>2</sub> fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)

The <sup>3</sup>He flux gauge in the Sargasso Sea: a determination of physical nutrient fluxes to the euphotic zone at the Bermuda Atlantic Time-series Site

Contact Info

Product

Resources

About

Nitrate isotopic composition between Bermuda and Puerto Rico: Implications for N2 fixation in the Atlantic Ocean

Abstract: . One important caveat is that fixed N in atmospheric deposition may contribute a significant proportion of the low-d 15 N N in the Sargasso Sea thermocline, in which case the relatively low rate we estimate for N 2 fixation would still be too high.

Cited by 127 publications

References 73 publications

Marine denitrification rates determined from a global 3-D inverse model

Marine denitrification rates determined from a global 3-D inverse model

N&lt;sub&gt;2&lt;/sub&gt; fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)

The &lt;sup&gt;3&lt;/sup&gt;He flux gauge in the Sargasso Sea: a determination of physical nutrient fluxes to the euphotic zone at the Bermuda Atlantic Time-series Site

Contact Info

Product

Resources

About

Nitrate isotopic composition between Bermuda and Puerto Rico: Implications for N₂ fixation in the Atlantic Ocean

N<sub>2</sub> fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)

The <sup>3</sup>He flux gauge in the Sargasso Sea: a determination of physical nutrient fluxes to the euphotic zone at the Bermuda Atlantic Time-series Site