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  • 11
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    In:  [Poster] In: WGOMD Workshop on High Resolution Ocean Climate Modeling, 07.-09.04.2014, Kiel, Germany .
    Publikationsdatum: 2014-12-09
    Beschreibung: Ocean biogeochemistry has a large effect on marine biogeochemical tracer distribution, comparable to that of circulation. However, the exact form of many biogeochemical processes, and therefore their parameterisation in global models, is not well known. Using the "Transport Matrix Method" (Khatiwala et al., 2005) as an offline tool to quickly equilibrate global coupled ocean biogeochemical models, we carry out sensitivity analyses to assess the skill of different biogeochemical, physical, and numerical setups. The ultimate aim is to find the "best" (with respect to metrics tailored for specific research questions) biogeochemical model, that may eventually be integrated into e.g. high-resolution models,or models that simulate transient scenarios.
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 12
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    In:  [Poster] In: EGU General Assembly 2015, 12.–17.04.2015 , Vienna, Austria .
    Publikationsdatum: 2019-09-23
    Beschreibung: Global biogeochemical ocean models are used to predict the future evolution of so-called oxygen minimum zones (OMZ), and the associated environmental and possible socio-economic impacts. Different models give different results and vary largely in their biogeochemical, physical and numerical setup. In order to assess the ability of the models to describe the present state as a necessary condition for skillful predictions into the future, they are usually compared against observed distributions of oxygen and other variables, such as thickness of oxygen minimum zones, nutrients, tracers for circulation and/or water mass age. We here examine different metrics for skill evaluation particularly of model representations of oxygen (and OMZs), for a wide range of global biogeochemical models. Among the metrics considered are Taylor plots, volume distributions of oxygen, volume of OMZ, preformed oxygen, and metrics that combine various diagnostic biogeochemical tracers. We finally investigate the impact these metrics may have for the “choice” of any best model, and discuss their applicability for different research or societal questions.
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 13
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    In:  [Poster] In: Oxygen Deoxygenation Conference 2018, 03.-07.09.2018, Kiel, Germany .
    Publikationsdatum: 2019-09-23
    Beschreibung: Simulated ENSO in climate models of the CMIP5 data base is still too divers to allow reliable predictions, how ENSO will change under global warming (Stocker et al. 2013). The atmospheric component of CGCMs was identified as major source of diversity (Lloyd et al. 2011). In many state-of-the-art CGCMs the positive (amplifying) atmospheric Bjerknes feedback and the negative (damping) heat flux feedback are both underestimated, leading to an error compensation (Bellenger et al. 2014, Bayr et al. 2018). Therefore, many CGCMs have biased ENSO dynamics, which hamper the simulation of strong El Niño events. During El Niño events the upwelling in the eastern Pacific is reduced and the thermocline is deeper than normal. Especially during strong El Niño events oxygen rich water is brought from the top into the OMZ (up to 300m depth), as observed during the strong El Niño in 1997 close to cost of Peru (Levin et al. 2002). As climate models with weak atmospheric feedbacks have problems in simulating strong El Niño events, this leads to a much weaker inflow of oxygen rich water into the OMZ from top in models with weak atmospheric feedbacks. We were able to produce in a series of perturbed physics experiments with the Kiel Climate Model (KCM) the same spread in ENSO atmospheric feedbacks then seen in the CMIP5 data base, due to different mean state climates in the tropical Pacific. In these KCM experiments we want to show the influence of the underestimated ENSO atmospheric feedbacks and biased ENSO dynamics on the simulation of the mean ocean circulation, the variability of the tropical ocean currents and the Pacific OMZ in coupled climate models.
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 14
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    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (24). pp. 8926-8934.
    Publikationsdatum: 2019-09-23
    Beschreibung: Previous studies found a negative trend in oxygen concentrations in tropical regions during the last decades. Employing a biogeochemical circulation model, we highlight the importance of wind driven ocean transport associated with the Subtropical-Tropical Cells (STCs) in setting the oxygen levels in the tropical ocean. The observed and simulated slowdown of the STCs by 30 percent from the 1960s to the 1990s caused a decrease in oxygen transport to the tropics. Transport of phosphate was similarly reduced, decreasing export production and respiration. The effects of physical transport and biological consumption partly compensate, damping oxygen interannual and decadal variability. Our results suggest that the observed residual oxygen trend in the tropical Pacific is mainly driven by changes in oxygen transport. Accordingly, the observed recent strengthening of the STCs leads us to expect a pause in the oxygen decrease or even an increase of tropical Pacific oxygen values in the near future.
    Materialart: Article , PeerReviewed
    Format: text
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 15
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    In:  [Talk] In: EUR-OCEANS Conference - Ocean deoxygenation and implications for marine biogeochemical cycles and ecosystems, 24.-26.10.2011, Toulouse, France .
    Publikationsdatum: 2012-02-23
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 16
    Publikationsdatum: 2013-12-13
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 17
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    In:  [Talk] In: IMBER Open Science Conference Future Oceans - Research for marine sustainability, 23.-27.06.2014, Bergen, Norway .
    Publikationsdatum: 2019-09-24
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 18
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    In:  [Invited talk] In: Max Planck Institute, Hamburg: Invited Seminar, 20.08.2014, Hamburg, Germany .
    Publikationsdatum: 2014-12-08
    Beschreibung: In order to understand the causes of the observed expansion of tropical ocean's oxygen minimum zones (OMZs), one need to disentangle the role of biogeochemical and circulation processes. In particular, the equatorial current system plays a major role in ventilating the eastern side of the Atlantic and Pacific basin. The role of this current system is evaluated comparing a coarse (0.5°) to an eddy resolving (0.1°) configuration (NEMO3.1 model). The improvement of OMZs in the eddy resolving configuration is traced to a stronger oxygen supply by a more realistic representation of the equatorial and off-equatorial undercurrents, outweighing the concurrent increase in oxygen consumption associated with the stronger nutrient supply. At a larger scale, the strength of the equatorial current system is associated with the Subtropical-Tropical Cells (STCs), which intensity depends of the wind forcing. We evaluate the impact of the STC variability on the oxygen content in the whole tropical Pacific ocean using a coarse (0.5°) configuration. Our results suggest that the observed recent strengthening of the STCs will lead to a pause in the oxygen decrease or even an increase of oxygen values in the near future.
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 19
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    In:  [Talk] In: Ocean Sciences Meeting 2010 "Oxygen Minimum Zones and Climate Change: Observations and Prediction IV", 22.02.-26.02.2010, Portland, Oregon, USA .
    Publikationsdatum: 2012-02-23
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 20
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    In:  [Talk] In: AGU Fall Meeting, 13.-17.12.2010, San Francisco, CA, USA .
    Publikationsdatum: 2012-02-23
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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