Equilibrator-based measurements of dissolved methane in the surface ocean using an integrated cavity output laser absorption spectrometer

Abstract. A laser-based analyser for nitrous oxide, carbon monoxide and water vapour was coupled to an equilibrator for continuous high-resolution dissolved gas measurements in the surface ocean. Results for nitrous oxide measurements from laboratory tests and field deployments are presented here. Short-term precision for 10 s-average N2O mole fractions at an acquisition rate of 1 Hz was better than 0.2 nmol mol−1 for standard gases and equilibrator measurements. The same precision was achieved for replicate standard gas analyses within 1 h of each other. The accuracy of the equilibrator measurements was verified by comparison with purge-and-trap GC-MS measurements of N2O concentrations in discrete samples from the Southern Ocean and showed agreement to within the 2% measurement uncertainty of the GC-MS method. Measured atmospheric N2O mole fractions agreed with AGAGE values to within 0.4%. The equilibrator response time to concentration changes in water was 142 to 203 s, depending on the headspace flow rate. The system was tested at sea during a north-to-south transect of the Atlantic Ocean. While the subtropical gyres were slightly undersaturated, the equatorial region was a source of nitrous oxide to the atmosphere. The ability to measure at high temporal and spatial resolution revealed sub-mesoscale variability in dissolved N2O concentrations. The magnitude of the observed saturation is in agreement with published data. Mean sea-to-air fluxes in the tropical and subtropical Atlantic ranged between −1.6 and 0.11 μmol m−2d−1 and confirm that the subtropical Atlantic is not an important source region for N2O to the atmosphere, compared to average global fluxes of 0.6 to 2.4 μmol m−2d−1. The system can be easily modified for autonomous operation on voluntary observing ships (VOS). Further work should include an interlaboratory comparison exercise with other methods of dissolved N2O analyses.

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Measurement of δ18O and δ2H of water and ethanol in wine by Off-Axis Integrated Cavity Output Spectroscopy and Isotope Ratio Mass Spectrometry

European Food Research and Technology ◽

10.1007/s00217-021-03758-2 ◽

2021 ◽

Author(s):

Xing Wang ◽

Henk G. Jansen ◽

Haico Duin ◽

Harro A. J. Meijer

Keyword(s):

Mass Spectrometry ◽

Isotope Ratio ◽

Isotope Analysis ◽

Isotope Ratio Mass Spectrometry ◽

Growth Conditions ◽

The Other ◽

H Nmr ◽

Cavity Output ◽

Pre Treatment ◽

Output Laser

AbstractThere are two officially approved methods for stable isotope analysis for wine authentication. One describes δ18O measurements of the wine water using Isotope Ratio Mass Spectrometry (IRMS), and the other one uses Deuterium-Nuclear Magnetic Resonance (2H-NMR) to measure the deuterium of the wine ethanol. Recently, off-axis integrated cavity output (laser) spectroscopy (OA-ICOS) has become an easier alternative to quantify wine water isotopes, thanks to the spectral contaminant identifier (SCI). We utilized an OA-ICOS analyser with SCI to measure the δ18O and δ2H of water in 27 wine samples without any pre-treatment. The OA-ICOS results reveal a wealth of information about the growth conditions of the wines, which shows the advantages to extend the official δ18O wine water method by δ2H that is obtained easily from OA-ICOS. We also performed high-temperature pyrolysis and chromium reduction combined with IRMS measurements to illustrate the “whole wine” isotope ratios. The δ18O results of OA-ICOS and IRMS show non-significant differences, but the δ2H results of both methods differ much more. As the δ2H difference between these two methods is mainly caused by ethanol, we investigated the possibility to deduce deuterium of wine ethanol from this difference. The results present large uncertainties and deviate from the obtained 2H-NMR results. The deviation is caused by the other constituents in the wine, and the uncertainty is due to the limited precision of the SCI-based correction, which need to improve to obtain the 2H values of ethanol as alternative for the 2H-NMR method.

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Scintillation and multiwavelength coherence effects in a long-path laser absorption spectrometer

Applied Optics ◽

10.1364/ao.17.000277 ◽

1978 ◽

Vol 17 (2) ◽

pp. 277 ◽

Cited By ~ 36

Author(s):

A. G. Kjelaas ◽

P. E. Nordal ◽

A. Bjerkestrand

Keyword(s):

Laser Absorption ◽

Coherence Effects ◽

Absorption Spectrometer

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Development of a tunable diode laser absorption spectrometer for measurements of the ratio in methane

Chemosphere ◽

10.1016/0045-6535(93)90409-x ◽

1993 ◽

Vol 26 (1-4) ◽

pp. 13-22 ◽

Cited By ~ 12

Author(s):

M. Schupp ◽

P. Bergamaschi ◽

G.W. Harris ◽

P.J. Crutzen

Keyword(s):

Diode Laser ◽

Tunable Diode Laser ◽

Laser Absorption ◽

Diode Laser Absorption ◽

Absorption Spectrometer

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Observations of Shallow Methane Bubble Emissions From Cascadia Margin

Frontiers in Earth Science ◽

10.3389/feart.2021.613234 ◽

2021 ◽

Vol 9 ◽

Author(s):

Anna P. M. Michel ◽

Victoria L. Preston ◽

Kristen E. Fauria ◽

David P. Nicholson

Keyword(s):

Water Column ◽

Water Depth ◽

Dissolved Methane ◽

Multibeam Sonar ◽

Surface Ocean ◽

Transient Nature ◽

Technological Approach ◽

Open Questions ◽

Cascadia Margin ◽

Methane Bubble

Open questions exist about whether methane emitted from active seafloor seeps reaches the surface ocean to be subsequently ventilated to the atmosphere. Water depth variability, coupled with the transient nature of methane bubble plumes, adds complexity to examining these questions. Little data exist which trace methane transport from release at a seep into the water column. Here, we demonstrate a coupled technological approach for examining methane transport, combining multibeam sonar, a field-portable laser-based spectrometer, and the ChemYak, a robotic surface kayak, at two shallow (<75 m depth) seep sites on the Cascadia Margin. We demonstrate the presence of elevated methane (above the methane equilibration concentration with the atmosphere) throughout the water column. We observe areas of elevated dissolved methane at the surface, suggesting that at these shallow seep sites, methane is reaching the air-sea interface and is being emitted to the atmosphere.

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