Low oxygen eddies in the eastern tropical North Atlantic: Implications for N2O cycling

Grundle, Damian S.; Löscher, Carolin R.; Krahmann, Gerd; Altabet, Mark A.; Bange, Hermann W.; Karstensen, Johannes; Körtzinger, Arne; Fiedler, Björn

doi:10.1038/s41598-017-04745-y

Cited by 30 publications

(33 citation statements)

References 52 publications

(97 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The standard deviations of five replicate measurements were 0.61, 0.33, 0.41 and 0.43‰ for δ 15 N α , δ 15 N β , δ 15 N bulk and δ 18 O values, respectively. These isotopic and isotopomeric precisions are on a par with those provided by GC/IRMS; and the PT‐CRDS setup has a routine sample size requirement ( ca 0.5 nmol‐N 2 O) two to three orders of magnitude lower than those of previous laser‐based N 2 O isotopomeric methods (Table ). The N 2 O‐ i reported isotope/isotopomer values of the four N 2 O reference materials (calibrated by GC/IRMS) based on factory settings, which resulted in slight inaccuracy, i.e.…”

Section: Resultsmentioning

confidence: 97%

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

Grundle

2019

Rapid Comm Mass Spectrometry

View full text Add to dashboard Cite

Rationale Nitrous oxide (N2O) is an atmospheric trace gas regulating Earth's climate, and is a key intermediate of many nitrogen cycling processes in aquatic ecosystems. Laser‐based technology for N2O concentration and isotopic/isotopomeric analyses has potential advantages, which include high analytical specificity, low sample size requirement and reduced cost. Methods An autosampler with a purge‐and‐trap module is coupled to a cavity ring‐down spectrometer to achieve automated and high‐throughput measurements of N2O concentrations, N2O isotope ratios (δ15Nbulk and δ18O values) and position‐specific isotopomer ratios (δ15Nα and δ15Nβ values). The system provides accuracy and precision similar to those for measurements made by traditional isotope ratio mass spectrometry (IRMS) techniques. Results The sample sizes required were 0.01–1.1 nmol‐N2O. Measurements of four N2O isotopic/isotopomeric references were cross‐calibrated with those obtained by IRMS. With a sample size of 0.50 nmol‐N2O, the measurement precision (1σ) for δ15Nα, δ15Nβ, δ15Nbulk and δ18O values was 0.61, 0.33, 0.41 and 0.43‰, respectively. Correction schemes were developed for sample size‐dependent isotopic/isotopomeric deviations. The instrumental system demonstrated consistent measurements of dissolved N2O concentrations, isotope/isotopomer ratios and production rates in seawater. Conclusions The coupling of an autosampler with a purge‐and‐trap module to a cavity ring‐down spectrometer not only significantly reduces sample size requirements, but also offers comprehensive investigation of N2O production pathways by the measurement of natural abundance and tracer level isotopes and isotopomers. Furthermore, the system can perform isotopic analyses of dissolved and solid nitrogen‐containing samples using N2O as the analytical proxy.

show abstract

Section: Resultsmentioning

confidence: 97%

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

Grundle

2019

Rapid Comm Mass Spectrometry

View full text Add to dashboard Cite

show abstract

“…7c) the respective NO One way to interpret this deficit is by NO − 3 loss through denitrification processes. Löscher et al (2015) and Grundle et al (2017) both found evidence for the onset of denitrification in the core of the ACME discussed here. Oxygen concentrations in the core are very low (about 3 µmol kg −1 ) and denitrification is possible.…”

Section: Nutrient Cycling In the Eddymentioning

confidence: 95%

“…Such an isolated core is the rarely observed case of an isolated volume of water in the open ocean and which allows one to study fundamental biogeochemical cycling processes in the absence of significant physical transport processes. A number of surprising biogeochemical cycling processes and ecosystem responses have been reported from the studies on eastern tropical North Atlantic low oxygen eddies (Löscher et al, 2015;Hauss et al, 2016;Fischer et al, 2016;Schütte et al, 2016b;Grundle et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

“…Oxygen concentrations in the core are very low (about 3 µmol kg −1 ) and denitrification is possible. Evidence for denitrification in the core of the ACME was, however, demonstrated as being important for nitrous oxide (N 2 O) cycling at the nanomolar range (Grundle et al, 2017), and not necessarily for overall NO − 3 losses, which are measured in the micromolar range. Grundle et al (2017) showed by relating nitrogen and phosphorous cycling that in the core of the ACME the NO − 3 losses were not detectable at the micromolar range.…”

Section: Nutrient Cycling In the Eddymentioning

confidence: 99%

“…Evidence for denitrification in the core of the ACME was, however, demonstrated as being important for nitrous oxide (N 2 O) cycling at the nanomolar range (Grundle et al, 2017), and not necessarily for overall NO − 3 losses, which are measured in the micromolar range. Grundle et al (2017) showed by relating nitrogen and phosphorous cycling that in the core of the ACME the NO − 3 losses were not detectable at the micromolar range. Thus, while denitrification may have played a minor role in causing the higher than expected AOU : NO − 3 ratio which we have calculated, it is unlikely that it contributed largely to the loss of 5 % of all NO remineralization.…”

Section: Nutrient Cycling In the Eddymentioning

confidence: 99%

See 2 more Smart Citations

Upwelling and isolation in oxygen-depleted anticyclonic modewater eddies and implications for nitrate cycling

et al. 2017

Self Cite

View full text Add to dashboard Cite

Abstract. The temporal evolution of the physical and biogeochemical structure of an oxygen-depleted anticyclonic modewater eddy is investigated over a 2-month period using high-resolution glider and ship data. A weakly stratified eddy core (squared buoyancy frequency N 2 ∼ 0.1 × 10 −4 s −2 ) at shallow depth is identified with a horizontal extent of about 70 km and bounded by maxima in N 2 . The upper N 2 maximum (3-5 × 10 −4 s −2 ) coincides with the mixed layer base and the lower N 2 maximum (0.4 × 10 −4 s −2 ) is found at about 200 m depth in the eddy centre. The eddy core shows a constant slope in temperature/salinity (T /S) characteristic over the 2 months, but an erosion of the core progressively narrows down the T /S range. The eddy minimal oxygen concentrations decreased by about 5 µmol kg −1 in 2 months, confirming earlier estimates of oxygen consumption rates in these eddies.Separating the mesoscale and perturbation flow components reveals oscillating velocity finestructure (∼ 0.1 m s −1 ) underneath the eddy and at its flanks. The velocity finestructure is organized in layers that align with layers in properties (salinity, temperature) but mostly cross through surfaces of constant density. The largest magnitude in velocity finestructure is seen between the surface and 140 m just outside the maximum mesoscale flow but also in a layer underneath the eddy centre, between 250 and 450 m. For both regions a cyclonic rotation of the velocity finestructure with depth suggests the vertical propagation of near-inertial wave (NIW) energy. Modification of the planetary vorticity by anticyclonic (eddy core) and cyclonic (eddy periphery) relative vorticity is most likely impacting the NIW energy propagation. Below the low oxygen core salt-finger type double diffusive layers are found that align with the velocity finestructure.Apparent oxygen utilization (AOU) versus dissolved inorganic nitrate (NO − 3 ) ratios are about twice as high (16) in the eddy core compared to surrounding waters (8.1). A large NO − 3 deficit of 4 to 6 µmol kg −1 is determined, rendering denitrification an unlikely explanation. Here it is hypothesized that the differences in local recycling of nitrogen and oxygen, as a result of the eddy dynamics, cause the shift in the AOU : NO − 3 ratio. High NO − 3 and low oxygen waters are eroded by mixing from the eddy core and entrain into the mixed layer. The nitrogen is reintroduced into the core by gravitational settling of particulate matter out of the euphotic zone. The low oxygen water equilibrates in the mixed layer by air-sea gas exchange and does not participate in the gravitational sinking. Finally we propose a mesoscalesubmesoscale interaction concept where wind energy, mediated via NIWs, drives nutrient supply to the euphotic zone and drives extraordinary blooms in anticyclonic mode-water eddies.

show abstract

Biogeochemical Role of Subsurface Coherent Eddies in the Ocean: Tracer Cannonballs, Hypoxic Storms, and Microbial Stewpots?

Frenger

Bianchi

Stührenberg

et al. 2018

Global Biogeochemical Cycles

View full text Add to dashboard Cite

Subsurface eddies are known features of ocean circulation, but the sparsity of observations prevents an assessment of their importance for biogeochemistry. Here we use a global eddying (0.1°) ocean‐biogeochemical model to carry out a census of subsurface coherent eddies originating from eastern boundary upwelling systems (EBUS) and quantify their biogeochemical effects as they propagate westward into the subtropical gyres. While most eddies exist for a few months, moving over distances of hundreds of kilometers, a small fraction (<5%) of long‐lived eddies propagates over distances greater than 1,000 km, carrying the oxygen‐poor and nutrient‐rich signature of EBUS into the gyre interiors. In the Pacific, transport by subsurface coherent eddies accounts for roughly 10% of the offshore transport of oxygen and nutrients in pycnocline waters. This “leakage” of subsurface waters can be a significant fraction of the transport by nutrient‐rich poleward undercurrents and may contribute to the well‐known reduction of productivity by eddies in EBUS. Furthermore, at the density layer of their cores, eddies decrease climatological oxygen locally by close to 10%, thereby expanding oxygen minimum zones. Finally, eddies represent low‐oxygen extreme events in otherwise oxygenated waters, increasing the area of hypoxic waters by several percent and producing dramatic short‐term changes that may play an important ecological role. Capturing these nonlocal effects in global climate models, which typically include noneddying oceans, would require dedicated parameterizations.

show abstract

Low oxygen eddies in the eastern tropical North Atlantic: Implications for N2O cycling

Cited by 30 publications

References 52 publications

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

Upwelling and isolation in oxygen-depleted anticyclonic modewater eddies and implications for nitrate cycling

Biogeochemical Role of Subsurface Coherent Eddies in the Ocean: Tracer Cannonballs, Hypoxic Storms, and Microbial Stewpots?

Contact Info

Product

Resources

About