Preprints
https://doi.org/10.5194/egusphere-2024-2049
https://doi.org/10.5194/egusphere-2024-2049
18 Jul 2024
 | 18 Jul 2024

Technical note: New approach for the determination of N2 fixation rates by coupling a membrane equilibrator to a mass spectrometer on voluntary observing ships

Sören Iwe, Oliver Schmale, and Bernd Schneider

Abstract. Nitrogen fixation by cyanobacteria plays an important role in the eutrophication of the Baltic Sea, since it promotes biomass production in the absence of dissolved inorganic nitrogen (DIN). Its contribution to the N budget is of the same order of magnitude as the combined sum of riverine and airborne DIN input, varying between 310 kt-N/yr and 792 kt-N/yr. The vast range is due to interannual variability, significant uncertainties in the various techniques used to determine N2 fixation and in extrapolating local studies to entire basins. To overcome some of the limitations we introduce a new approach using a Gas Equilibrium – Membrane-Inlet Mass Spectrometer (GE-MIMS). A membrane contactor (Liquicel) is utilized to establish gas phase equilibrium for atmospheric gases dissolved in seawater. The mole fractions for N2, Ar and O2 in the gas phase are determined continuously by mass spectrometry and yield the concentration of these gases by multiplication with the total pressure and the respective solubility constants. The results from laboratory tests show that the accuracy (deviation from expected values): N2: 0.20 %, Ar: 0.70 %, O2: 0.20 % and the precision (2 times the absolute standard deviation) N2: 0.05 %, Ar: 0.14 %, O2: 0.11 % is sufficient enough to detect and quantify nitrogen fixation. The e-folding equilibration time is 4.8 min for N2, 3.0 min for Ar and 3.2 min for O2. The GE-MIMS is designed for deployment on a voluntary observing ship (VOS), enabling repeated transects along the same route and providing high temporal and spatial resolution data. Therefore, the method is suitable for offering large-scale records of the surface water N2 depletion and of Ar to account for the air-sea gas exchange. Additional O2 measurements will be utilized to estimate the net community production (NCP) triggered by N2 fixation.

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Sören Iwe, Oliver Schmale, and Bernd Schneider

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2049', Anonymous Referee #1, 08 Aug 2024
    • AC1: 'Reply on RC1', Sören Iwe, 25 Sep 2024
  • RC2: 'Comment on egusphere-2024-2049', Anonymous Referee #2, 05 Sep 2024
    • AC2: 'Reply on RC2', Sören Iwe, 25 Sep 2024
  • RC3: 'Comment on egusphere-2024-2049', Anonymous Referee #3, 06 Sep 2024
    • AC3: 'Reply on RC3', Sören Iwe, 25 Sep 2024
Sören Iwe, Oliver Schmale, and Bernd Schneider

Data sets

Characterizing the Gas Equilibrium - Membrane-Inlet Mass Spectrometer (GE-MIMS) through Laboratory Data Sören Iwe http://doi.io-warnemuende.de/10.12754/data-2024-0014

Sören Iwe, Oliver Schmale, and Bernd Schneider

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Short summary
We present a novel method to quantify N2 fixation by cyanobacteria, crucial in Baltic Sea eutrophication. Our Gas Equilibrium – Membrane-Inlet Mass Spectrometer (GE-MIMS), designed for operation on voluntary observing ships (VOS), enables large-scale monitoring of surface water N2 depletion caused by N2 fixation. Laboratory tests confirm the device’s accuracy and precision, ensuring it can complement current methods and contribute valuable data to better understand N2 fixation in the Baltic Sea.