N isotopic composition of dissolved organic nitrogen and nitrate at the Bermuda Atlantic Time‐series Study site

Knapp, Angela N.; Sigman, Daniel M.; Lipschultz, Fredric

doi:10.1029/2004gb002320

Cited by 310 publications

(411 citation statements)

References 69 publications

(183 reference statements)

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“…Another explanation would be that nitrogen fixation accounts for the same amount of new production as is fueled by upwelled nutrients (0.5 to 1 mol N m −2 y −1 ). However, current estimates of nitrogen fixation in the Sargasso sea are much lower, ranging from so low as to be nondetectable in N isotopic studies (Knapp et al, 2005) to 0.015 mol N m −2 y −1 (Orcutt et al, 2001) to 0.072 mol N m −2 y −1 (Gruber and Sarmiento, 1997).…”

Section: Synthesismentioning

confidence: 99%

“…It does not take into account nitrogen fixation. Nitrogen fixation, however, is estimated to be only a small fraction of the new production at BATS (Orcutt et al, 2001;Hansell et al, 2004;Knapp et al, 2005) and thus this omission does not contribute to much error in the estimate of new production. Instead, the largest source of uncertainty in the 3 He flux gauge estimate of new production stems from the interpretation of the air-sea 3 He flux and the 3 He and NO − 3…”

Section: Type Of Productionmentioning

confidence: 99%

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A determination of air-sea gas exchange and upper ocean biological production from five noble gases and tritiugenic helium-3

Stanley¹

2007

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The five noble gases (helium, neon, argon, krypton, and xenon) are biologically and chemically inert, making them ideal oceanographic tracers. Additionally, the noble gases have a wide range of solubilities and molecular diffusivities, and thus respond differently to physical forcing. Tritium, an isotope of hydrogen, is useful in tandem with its daughter helium-3 as a tracer for water mass ages. In this thesis, a fourteen month time-series of the five noble gases, helium-3 and tritium was measured at the Bermuda Atlantic Time-series Study (BATS) site. The time-series of five noble gases was used to develop a parameterization of air-sea gas exchange for oligotrophic waters and wind speeds between 0 and 13 m s −1 that explicitly includes bubble processes and that constrains diffusive gas exchange to ± 6% and complete and partial air injection processes to ± 15%. Additionally, the parameterization is based on weeks to seasonal time scales, matching the time scales of many relevant biogeochemical cycles. The time-series of helium isotopes, tritium, argon, and oxygen was used to constrain upper ocean biological production. Specifically, the helium flux gauge technique was used to estimate new production, apparent oxygen utilization rates were used to quantify export production, and euphotic zone seasonal cycles of oxygen and argon were used to determine net community production. The concurrent use of these three methods allows examination of the relationship between the types of production and begins to address a number of apparent inconsistencies in the elemental budgets of carbon, oxygen, and nitrogen.

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Section: Synthesismentioning

confidence: 99%

Section: Type Of Productionmentioning

confidence: 99%

A determination of air-sea gas exchange and upper ocean biological production from five noble gases and tritiugenic helium-3

Stanley¹

2007

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“…Though not discussed here, these methods were also used for NO d 15 N of DON-Because there is almost no DIN in the epilimnion water column of Lake Kinneret in summer and autumn, the only other dissolved combined nitrogen fraction is DON. The persulfate oxidation method was used to convert DON to NO { 3 (Knapp et al 2005). 14-mL samples were reacted with 6 mL of reagent (175 mL of 1 mol L 21 NaOH plus 25 g of recrystallized K 2 S 2 O 8 made up to 500 mL with distilled H 2 O) for 3 h at 100uC.…”

Section: Methodsmentioning

confidence: 99%

Seasonally varying nitrogen isotope biogeochemistry of particulate organic matter in Lake Kinneret, Israel

2009

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Large temporal variations in the nitrogen isotopic composition (d 15 N) of particulate organic matter (POM) and dissolved inorganic nitrogen (DIN) species in Lake Kinneret occurred in response to seasonal phasing of dominant nitrogen cycle processes. The lowest d 15 N POM values (25.5%) were observed in early winter, a consequence of isotopic fractionation by chemoautotrophic microbial NH Oligotrophic conditions are found in the epilimnion in late summer and early autumn and low (3.3%) d 15 N POM was found during the bloom of the filamentous N 2 -fixing cyanobacteria Aphanizomenon ovalisporum and Cylindrospermopsis cuspis. The d 15 N-dissolved organic nitrogen isotopic signature at this time was significantly higher, 8-12%, suggesting a phytoplankton source from earlier in the seasonal cycle. Overall, the largest known seasonal variations in N isotope composition have been observed in Lake Kinneret, providing a uniquely useful biogeochemical tool for studying N cycling in lakes as well as detecting long-term changes in N source and cycling in response to watershed land use changes and climate change.

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“…and TDN samples, a range of standards (glycine, and amino caproic acid) were oxidized with samples (concentrations of 1, 5, and 10 mg N L -1 , representing the range of sample concentrations). Resulting reagent blanks derived from purified (recrystallized three times) ACS-grade peroxodisulfate (K 2 S 2 O 8 ) solutions were removed from each resulting d 15 N value on a per batch basis (Knapp et al 2005). The analytical precision of oxidized samples duplicated between runs was on average different by 1.29 % (n = 12) and 0.49 % (n = 10) for NH 4…”

Section: Soil Nutrient Samplingmentioning

confidence: 99%

“…Diluted (0.5 M salt) aliquots (1.5 mL) of total dissolved N (TDN) and cation resin ammonium extracts were converted to nitrate using potassium peroxodisulfate thermo-oxidation (Cabrera and Beare 1993;Doyle et al 2004), and converted to N 2 O gas for determination of d 15 N and d 18 O values using anaerobic cultures of Pseudomonas aureofasciens denitrifying bacteria (Sigman et al 2001;Knapp et al 2005). This yielded d 15 N values for TDN in KCl extracts, d 15 N of ammonium in cation resin extracts, and d 15 N and d 18 O values in both KCl and anion resin nitrate extracts.…”

Section: Soil Nutrient Samplingmentioning

confidence: 99%

Stable nitrogen isotope patterns of trees and soils altered by long-term nitrogen and phosphorus addition to a lowland tropical rainforest

et al. 2014

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Foliar nitrogen (N) isotope ratios (d 15 N) are used as a proxy for N-cycling processes, including the ''openness'' of the N cycle and the use of distinct N sources, but there is little experimental support for such proxies in lowland tropical forest. To address this, we examined the d 15 N values of soluble soil N and canopy foliage of four tree species after 13 years of factorial N and P addition to a mature lowland rainforest. We hypothesized that N addition would lead to 15 Nenriched soil N forms due to fractionating losses, whereas P addition would reduce N losses as the plants and microbes adjusted their stoichiometric demands. Chronic N addition increased the concentration and d 15 N value of soil nitrate and d 15 N in live and senesced leaves in two of four tree species, but did not affect ammonium or dissolved organic N. Phosphorus addition significantly increased foliar d 15 N in one tree species and elicited significant N 9 P interactions in two others due to a reduction in foliar d 15 N enrichment under N and P co-addition. Isotope mixing models indicated that three of four tree species increased their use of nitrate relative to ammonium following N addition, supporting the expectation that tropical trees use the most available form of mineral N. Previous observations that anthropogenic N deposition in this tropical region have led to increasing foliar d 15 N values over decadal time-scales is now mechanistically linked to greater usage of 15 N-enriched nitrate.

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N isotopic composition of dissolved organic nitrogen and nitrate at the Bermuda Atlantic Time‐series Study site

Cited by 310 publications

References 69 publications

A determination of air-sea gas exchange and upper ocean biological production from five noble gases and tritiugenic helium-3

A determination of air-sea gas exchange and upper ocean biological production from five noble gases and tritiugenic helium-3

Seasonally varying nitrogen isotope biogeochemistry of particulate organic matter in Lake Kinneret, Israel

Stable nitrogen isotope patterns of trees and soils altered by long-term nitrogen and phosphorus addition to a lowland tropical rainforest

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