نبذة مختصرة : Upwelling systems are significant sources of atmospheric nitrous oxide (N₂O). The Benguela Upwelling System is one of the most productive regions worldwide and a temporally variable source of N₂O. Strong O₂ depletions above the shelf are favoring periodically OMZ formations. We aimed to assess underlying N₂O production and consumption processes on different temporal and spatial scales during austral winter in the Benguela Upwelling System, when O₂⁻deficiency in the water column is relatively low. The fieldwork took place during the cruise M157 (August 4ᵗʰ – September 16ᵗʰ 2019) onboard the R/V METEOR. This expedition included four close-coastal regions around Walvis Bay at 23°S, which presented the lowest O₂ concentrations near the seafloor and thus may provide hotspots of N₂O production. Seawater was collected in 10 L free-flow bottles by using a rosette system equipped with conductivity-temperature-depth (CTD) sensors (SBE 911plus, Seabird-electronics, USA).Seawater samples were collected from 10 L free-flow bottles bubble-free, filled into 200 mL serum bottles and immediately fixed with saturated mercury chloride (HgCl₂). Concentrations of dissolved N₂O were measured by a purge and trap system using a dynamic headspace (Sabbaghzadeh et al., 2021). The N₂O gas saturation (N₂Oₛₐₜ in %) was calculated from the concentration ratio between the seawater sample and seawater equilibrated with the atmosphere. ∆N₂O (N₂O saturation disequilibrium in nmol L⁻¹) was calculated as the difference between the measured N₂O concentration and the atmospheric equilibrium N₂O concentration using Bunsen solubility coefficient (Weiss and Price, 1980). AOU (apparent oxygen utilization in µmol L⁻¹) expresses the O₂ consumption by microbial respiration and was calculated as the difference between the equilibrated O₂ and observed O₂ concentration with the same physico-chemical properties (Weiss and Price, 1980).
Relation: Dangl, Gabriela; Frey, Claudia; Hassenrück, Christiane; Sabbaghzadeh, Bita; Wäge-Recchioni, Janine; Lehmann, Moritz F; Ley, Martin; Rehder, Gregor; Jürgens, Klaus (2023): 16S amplicon sequences of the microbial communities in the water column of the Northern Benguela Upwelling System [dataset]. European Nucleotide Archive (ENA), https://www.ebi.ac.uk/ena/browser/view/PRJEB60503; Dangl, Gabriela; Frey, Claudia; Hassenrück, Christiane; Sabbaghzadeh, Bita; Wäge-Recchioni, Janine; Lehmann, Moritz F; Ley, Martin; Rehder, Gregor; Jürgens, Klaus (2023): Inorganic nutrient measurements in the Benguela Upwelling System during METEOR cruise M157 [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.956014; Dangl, Gabriela; Frey, Claudia; Hassenrück, Christiane; Sabbaghzadeh, Bita; Wäge-Recchioni, Janine; Lehmann, Moritz F; Ley, Martin; Rehder, Gregor; Jürgens, Klaus (2023): Nitrous oxide production rates and stable isotopes in the Benguela Upwelling System during METEOR cruise M157 [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.956016; Dangl, Gabriela; Frey, Claudia; Hassenrück, Christiane; Sabbaghzadeh, Bita; Wäge-Recchioni, Janine; Lehmann, Moritz F; Ley, Martin; Rehder, Gregor; Jürgens, Klaus (2023): Water and sediment metagenomes from the Northern Benguela Upwelling System (cruise M157) [dataset]. European Nucleotide Archive (ENA), https://www.ebi.ac.uk/ena/browser/view/PRJEB63098; Sabbaghzadeh, Bita; Glockzin, Michael; Rehder, Gregor (2022): Trace gases air daily means during METEOR cruise M157 [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.946811; Zabel, Matthias (2020): Short Cruise Report RV METEOR Cruise M157. Expeditionsarchiv FS METEOR, 13, https://www.ldf.uni-hamburg.de/meteor/wochenberichte/wochenberichte-meteor/m156-m159/m157-scr.pdf, https://download.pangaea.de/reference/117368/attachments/m157-scr.pdf; Sabbaghzadeh, Bita; Arévalo-Martínez, Damian L; Glockzin, Michael; Otto, Stefan; Rehder, Gregor (2021): Meridional and Cross‐Shelf Variability of N 2 O and CH 4 in the Eastern‐South Atlantic. Journal of Geophysical Research: Oceans, 126(11), https://doi.org/10.1029/2020JC016878; Weiss, Ray F; Price, B A (1980): Nitrous oxide solubility in water and seawater. Marine Chemistry, 8(4), 347-359, https://doi.org/10.1016/0304-4203(80)90024-9; https://doi.pangaea.de/10.1594/PANGAEA.955991; https://doi.org/10.1594/PANGAEA.955991
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