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  • 1
    Keywords: Hochschulschrift ; Pazifischer Ozean Süd ; Stickstoffkreislauf
    Type of Medium: Online Resource
    Pages: Online-Ressource
    DDC: 550
    Language: English
    Note: Kiel, Univ., Diss., 2015
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  • 2
    Publication Date: 2021-06-27
    Description: Ocean deoxygenation is a threat to marine ecosystems. We evaluated the potential of two ocean intervention technologies, that is, “artificial downwelling (AD)” and “artificial upwelling (AU),” for remedying the expansion of Oxygen Deficient Zones (ODZs). The model‐based assessment simulated AD and AU implementations for 80 years along the eastern Pacific ODZ. When AD was simulated by pumping surface seawater to the 178–457 m‐depth range of the ODZ, vertically integrated oxygen increased by up to 4.5% in the deployment region. Pumping water from 457 m depth to the surface (i.e., AU), where it can equilibrate with the atmosphere, increased the vertically integrated oxygen by 1.03%. However, both simulated AD and AU increased biological production via enhanced nutrient supply to the sea surface, resulting in enhanced export production and subsequent aerobic remineralization also outside of the actual implementation region, and an ultimate net decline of global oceanic oxygen.
    Description: Key Points: Artificial downwelling (AD) and upwelling (AU) in the eastern Pacific oxygen deficient region are simulated in a global model Both technologies can effectively mitigate local expansion of intermediate‐depth oceanic oxygen deficient zones under climate change Global deoxygenation is however enhanced due to increased export production and aerobic respiration resulting from AD and AU
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: German Research Foundation (DFG)
    Keywords: 551.46 ; deoxygenation ; geoengineering ; artificial upwelling ; artificial downwelling ; Earth system model ; marine hypoxia
    Type: article
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  • 3
    Publication Date: 2021-03-18
    Description: Highlights: • Optimality-based modelling of microzooplankton trophic interactions in mesocsosm ecosystems. • Intraguild predation is important for modelling microzooplankton feeding interactions. • Trophic interactions structured solely by size may fail to capture feeding diversity. • Adequate representation of feeding interaction is needed for modelling ecosystem dynamics. Abstract: The zooplankton components in biogeochemical models drive top-down control of primary production and remineralisation, and thereby exert a strong impact on model performance. Who eats whom in oceanic plankton ecosystem models is often largely determined by body size. However, zooplankton of similar size can have different prey-size spectra. Thus, models with solely size-structured trophic interactions may not capture the full diversity of feeding interactions and miss important parts of zooplankton behavior. We apply an optimality-based plankton ecosystem model to analyse trophic interactions in a suite of mesocosm experiments in the Peruvian upwelling region. Sensitivity analyses reveal a dominant role of trophic structure for model performance, which cannot be compensated by parameter optimisation. The single most important aspect governing model performance is the trophic linking between dinoflagellates and ciliates. Only with a bidirectional link, i.e., both groups can prey on each other, is the model able to reproduce the differential development of the microzooplankton communities in the mesocosms. Thus, we conclude that a solely size-based trophic structure may not be appropriate to represent the most important trophic interactions in plankton ecosystems. The diversity of feeding interactions needs to be adequately represented to capture community dynamics.
    Type: Article , PeerReviewed
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  • 4
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    China Academic Journal (CD) Electronic Journals Publishing House Co
    In:  Xiandai-yixue-jinzhan = Progress in Modern Biomedicine, 9 (10). pp. 1874-1877.
    Publication Date: 2019-01-21
    Type: Article , PeerReviewed
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  • 5
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    In:  [Poster] In: DynaTrait Annual Meeting, 14.-17.09.2015, Hannover, Germany .
    Publication Date: 2016-02-05
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
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    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 12 . pp. 1113-1130.
    Publication Date: 2017-12-19
    Description: Local coupling between nitrogen fixation and denitrification in current biogeochemical models could result in runaway feedback in open-ocean oxygen minimum zones (OMZs), eventually stripping OMZ waters of all fixed nitrogen. This feedback does not seem to operate at full strength in the ocean, as nitrate does not generally become depleted in open-ocean OMZs. To explore in detail the possible mechanisms that prevent nitrogen depletion in the OMZ of the eastern tropical South Pacific (ETSP), we develop a box model with fully prognostic cycles of carbon, nutrients and oxygen in the upwelling region and its adjacent open ocean. Ocean circulation is calibrated with Δ14C data of the ETSP. The sensitivity of the simulated nitrogen cycle to nutrient and oxygen exchange and ventilation from outside the model domain and to remineralization scales inside an OMZ is analysed. For the entire range of model configurations explored, we find that the fixed-N inventory can be stabilized at non-zero levels in the ETSP OMZ only if the remineralization rate via denitrification is slower than that via aerobic respiration. In our optimum model configuration, lateral oxygen supply into the model domain is required at rates sufficient to oxidize at least about one fifth of the export production in the model domain to prevent anoxia in the deep ocean. Under these conditions, our model is in line with the view of phosphate as the ultimate limiting nutrient for phytoplankton, and implies that for the current notion of nitrogen fixation being favoured in N-deficit waters, the water column of the ETSP could even be a small net source of nitrate.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 7
    Publication Date: 2019-02-01
    Description: Both atmospheric deposition and benthic remineralisation influence the marine nitrogen cycle, and hence ultimately also marine primary production. The biological and biogeochemical relations in the eastern tropical South Pacific (ETSP) among nitrogen deposition, benthic denitrification and phosphorus regeneration are analysed in a prognostic box model of the oxygen, nitrogen and phosphorus cycles in the ETSP. Atmospheric nitrogen deposition ( ≈ 1.5 Tg N yr−1 for the years 2000–2009) is offset by half in the model by reduced N2 fixation, with the other half transported out of the model domain. Model- and data-based benthic denitrification in our model domain are responsible for losses of 0.19 and 1.0 Tg Tg N yr−1, respectively, and both trigger nitrogen fixation, partly compensating for the NO3− loss. Model- and data-based estimates of enhanced phosphate release via sedimentary phosphorus regeneration under suboxic conditions are 0.062 and 0.11 Tg N yr−1, respectively. Since phosphate is the ultimate limiting nutrient in the model, even very small additional phosphate inputs stimulate primary production and subsequent export production and NO3− loss in the oxygen minimum zone (OMZ). A sensitivity analysis of the local response to both atmospheric deposition and benthic remineralisation indicates dominant stabilising feedbacks in the ETSP, which tend to keep a balanced nitrogen inventory; i.e. nitrogen input by atmospheric deposition is counteracted by decreasing nitrogen fixation; NO3− loss via benthic denitrification is partly compensated for by increased nitrogen fixation; enhanced nitrogen fixation stimulated by phosphate regeneration is partly counteracted by stronger water-column denitrification. Even though the water column in our model domain acts as a NO3− source, the ETSP including benthic denitrification might be a NO3− sink.
    Type: Article , PeerReviewed
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  • 8
    Publication Date: 2021-02-08
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 9
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    Zhongguo-Haiyang-Daxue
    In:  Zhongguo-Haiyang-Daxue-xuebao = Periodical of Ocean University of China, 40 (3). pp. 95-100.
    Publication Date: 2016-04-22
    Description: A marine bacterium Pseudoalteromonas sp.QY202 with high κ-carrageenase activity was isolated from the surface of Chondrus crispus.The κ-carrageenase was purified to electrophoretic homogeneity from the culture supernatant by a procedure of ammonium sulfate precipitation,desalting and DEAE-sepharose ion exchange chromatography,and the characterization of the enzyme was studied.The results show that the enzyme is purified 23.1 folds with a total recovery yield of 43.9% and gives a single band on SDS-PAGE with a molecular mass of 33.2 kDa.The optimum temperature and pH for enzyme activity are 40 ℃ and pH8.0,respectively.The enzyme is stable at temperatures below 40 ℃ and over a range of pH7.0-8.0.For κ-carrageenan,the enzyme gave a Km value of 1.6 mg/mL.The enzyme activity could be enhanced by the presence of Na+ and K+,whereas enormously inhibited by Hg^2+and Cu^2+.The main hydrolysis products of κ-carrageenan by the enzyme are κ-neocarradiaose and κ-neocarratetraose.
    Type: Article , NonPeerReviewed
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  • 10
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    In:  [Talk] In: Gulf of Maine Research Institute (GMRI) science seminar series, 20.01.2021, Online .
    Publication Date: 2021-02-08
    Type: Conference or Workshop Item , NonPeerReviewed
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