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  • 1
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    Nitrous oxide during the onset of the Atlantic Cold Tongue (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 122 (1). pp. 171-184.
    Details
    Publikationsdatum: 2020-02-06
    Beschreibung: The tropical Atlantic exerts a major influence in climate variability through strong air-sea interactions. Within this region, the eastern side of the equatorial band is characterized by strong seasonality, whereby the most prominent feature is the annual development of the Atlantic Cold Tongue (ACT). This band of low sea surface temperatures (∼22-23°C) is typically associated with upwelling-driven enhancement of surface nutrient concentrations and primary production. Based on a detailed investigation of the distribution and sea-to-air fluxes of N2O in the eastern equatorial Atlantic (EEA), we show that the onset and seasonal development of the ACT can be clearly observed in surface N2O concentrations, which increase progressively as the cooling in the equatorial region proceeds during spring-summer. We observed a strong influence of the surface currents of the EEA on the N2O distribution, which allowed identifying “high” and “low” concentration regimes that were, in turn, spatially delimited by the extent of the warm eastward-flowing North Equatorial Countercurrent and the cold westward-flowing South Equatorial Current. Estimated sea-to-air fluxes of N2O from the ACT (mean 5.18±2.59 µmol m−2 d−1) suggests that in May-July 2011 this cold-water band doubled the N2O efflux to the atmosphere with respect to the adjacent regions, highlighting its relevance for marine tropical emissions of N2O. This article is protected by copyright. All rights reserved.
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1002/2016JC012238
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  • 2
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    Hydroxylamine as a potential indicator of nitrification in the open ocean (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 46 (4). pp. 2158-2166.
    Details
    Publikationsdatum: 2022-01-31
    Beschreibung: Hydroxylamine (NH 2 OH), a short-lived intermediate in the nitrogen cycle, is a potential precursor of nitrous oxide (N 2 O) in the ocean. However, measurements of NH 2 OH in the ocean are sparse. Here we present a data set of depth profiles of NH 2 OH from the equatorial Atlantic Ocean and the eastern tropical South Pacific and compare it to N 2 O, nitrate, and nitrite profiles under varying oxygen conditions. The presence of NH 2 OH in surface waters points toward surface nitrification in the upper 100 m. Overall, we found a ratio of 1:3 between NH 2 OH and N 2 O in open ocean areas when oxygen concentrations were 〉50 μmol/L. In the equatorial Atlantic Ocean and the open ocean eastern tropical South Pacific, where nitrification is the dominant N 2 O production pathway, stepwise multiple regressions demonstrated that N 2 O, NH 2 OH, and nitrate concentrations were highly correlated, suggesting that NH 2 OH is a potential indicator for nitrification.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2018GL080466
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  • 3
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    N2O emissions from the northern Benguela upwelling system (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 46 (6). pp. 3317-3326.
    Details
    Publikationsdatum: 2022-01-31
    Beschreibung: The Benguela Upwelling system (BUS) is the most productive of all eastern boundary upwelling ecosystems and it hosts a well‐developed oxygen minimum zone. As such, the BUS is a potential hotspot for production of N2O, a potent greenhouse gas derived from microbially‐driven decay of sinking organic matter. Yet, the extent at which near‐surface waters emit N2O to the atmosphere in the BUS is highly uncertain. Here we present the first high‐resolution surface measurements of N2O across the northern part of the BUS (nBUS). We found strong gradients with a three‐fold increase in N2O concentrations near the coast as compared with open ocean waters. Our observations show enhanced sea‐to‐air fluxes of N2O (up to 1.67 nmol m−2 s−1) in association with local upwelling cells. Based on our data we suggest that the nBUS can account for 13% of the total coastal upwelling source of N2O to the atmosphere.
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1029/2018GL081648
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  • 4
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    Meridional and Cross‐Shelf Variability of N2O and CH4 in the Eastern‐South Atlantic (2021)
    AGU (American Geophysical Union) | Wiley
    Details
    Publikationsdatum: 2024-02-07
    Beschreibung: Upward transport and/or mixing of trace gas-enriched subsurface waters fosters the exchange of nitrous oxide (N2O) and methane (CH4) with the atmosphere in the Eastern-South Atlantic (ESA). To date, it is, however, unclear whether this source is maintained by local production or advection of trace gas-enriched water masses. The meridional and zonal variability of N2O and CH4 in the ESA were investigated to identify the contributions of the major regional water masses to the overall budget of N2O and CH4. The maximal sea surface N2O and CH4 concentrations and the main ESA upwelling cells co-occurred with a strong negative correlation with the sea surface temperature (SST) (p 〈 0.05). The dominance of the central water masses in the winter and spring seasons and the interplay between shelf topography and wind regime are suggested to determine enhanced gas transfer toward the sea-air interface or “capping” at midwater depth. These parameters are supposed to be critical in the local budget of N2O and CH4 in the ESA. Our findings also show that the shape of N2O and CH4 gradients is very similar both meridionally and zonally; however, the extent of the differences between the high-end and low-end members of the concentrations/saturations range is different. This suggests a more pronounced effect of local sources on CH4 than N2O distribution, in particular in the Walvis Bay area. With respect to N2O, however, low-oxygen waters from the poleward undercurrent impinge in the shelf close to Cape Frio and often result in N2O concentrations significantly higher than off Lüderitz (p 〈 0.05)
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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