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  • 2015-2019  (33)
  • 1
    Online Resource
    Online Resource
    The influence of phytoplankton aggregation on sedimentation : a model study (2018)
    Kiel
    Details Availability
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: Online-Ressource (134 Seiten = 3,5 MB) , Illustration, Graphen
    URL: http://oceanrep.geomar.de/44266/
    Language: English
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 2
    Online Resource
    Online Resource
    Zooplankton mortality effects on the biogeochemistry of the upwelling system off Peru (2018)
    Kiel
    Details Availability
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (122 Blatt = 60 MB) , Illustrationen, Graphen, Karten
    URL: http://oceanrep.geomar.de/45160/
    Language: English
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    GEOMAR CATALOGUE
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  • 3
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    Biological and physical influences on marine snowfall at the equator (2017)
    Nature Research
    In:  Nature Geoscience, 10 (11). pp. 852-858.
    Details
    Publication Date: 2020-06-18
    Description: High primary productivity in the equatorial Atlantic and Pacific oceans is one of the key features of tropical ocean biogeochemistry and fuels a substantial flux of particulate matter towards the abyssal ocean. How biological processes and equatorial current dynamics shape the particle size distribution and flux, however, is poorly understood. Here we use high-resolution size-resolved particle imaging and Acoustic Doppler Current Profiler data to assess these influences in equatorial oceans. We find an increase in particle abundance and flux at depths of 300 to 600 m at the Atlantic and Pacific equator, a depth range to which zooplankton and nekton migrate vertically in a daily cycle. We attribute this particle maximum to faecal pellet production by these organisms. At depths of 1,000 to 4,000 m, we find that the particulate organic carbon flux is up to three times greater in the equatorial belt (1° S–1° N) than in off-equatorial regions. At 3,000 m, the flux is dominated by small particles less than 0.53 mm in diameter. The dominance of small particles seems to be caused by enhanced active and passive particle export in this region, as well as by the focusing of particles by deep eastward jets found at 2° N and 2° S. We thus suggest that zooplankton movements and ocean currents modulate the transfer of particulate carbon from the surface to the deep ocean.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: video
    Format: video
    Format: video
    Format: video
    Format: video
    DOI: 10.1038/ngeo3042
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Calibrating a global three-dimensional biogeochemical ocean model (MOPS-1.0) (2017)
    Copernicus Publications (EGU)
    In:  Geoscientific Model Development, 10 . pp. 127-154.
    Details
    Publication Date: 2020-02-06
    Description: Global biogeochemical ocean models contain a variety of different biogeochemical components and often much simplified representations of complex dynamical interactions, which are described by many (≈10–≈100) parameters. The values of many of these parameters are empirically difficult to constrain, due to the fact that in the models they represent processes for a range of different groups of organisms at the same time, while even for single species parameter values are often difficult to determine in situ. Therefore, these models are subject to a high level of parametric uncertainty. This may be of consequence for their skill with respect to accurately describing the relevant features of the present ocean, as well as their sensitivity to possible environmental changes. We here present a framework for the calibration of global biogeochemical ocean models on short and long time scales. The framework combines an offline approach for transport of biogeochemical tracers with an Estimation of Distribution Algorithm (Covariance Matrix Adaption Evolution Strategy, CMAES). We explore the performance and capability of this framework by five different optimizations of six biogeochemical parameters of a global biogeochemical model. First, a twin experiment explores the feasibility of this approach. Four optimizations against a climatology of observations of annual mean dissolved nutrients and oxygen determine the extent, to which different setups of the optimization influence model's fit and parameter estimates. Because the misfit function applied focuses on the large-scale distribution of inorganic biogeochemical tracers, parameters that act on large spatial and temporal scales are determined earliest, and with the least spread. Parameters more closely tied to surface biology, which act on shorter time scales, are more difficult to determine. In particular the search for optimum zooplankton parameters can benefit from a sound knowledge of maximum and minimum parameter values, leading to a more efficient optimization. It is encouraging that, although the misfit function does not contain any direct information about biogeochemical turnover, the optimized models nevertheless provide a better fit to observed global biogeochemical fluxes.
    Type: Article , PeerReviewed
    Format: text
    Format: archive
    DOI: 10.5194/gmd-10-127-2017
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Modelling the role of marine particle on large scale 231Pa, 230Th, Iron and Aluminium distributions (2015)
    Elsevier
    In:  Progress in Oceanography, 133 . pp. 66-72.
    Details
    Publication Date: 2019-09-23
    Description: Highlights: • We examine the role of marine particle for regulating trace element distribution. • We review the state of the art for modelling the oceanic distribution of specific tracers: Thorium, Protactinium, Iron, and Aluminium. • We review the state of the art for modelling particle distribution in large scale ocean biogeochemical model. The distribution of trace elements in the ocean is governed by the combined effects of various processes, and by exchanges with external sources. Modelling these represents an opportunity to better understand and quantify the mechanisms that regulate the oceanic tracer cycles. Observations collected during the GEOTRACES program provide an opportunity to improve our knowledge regarding processes that should be considered in biogeochemical models to adequately represent the distributions of trace elements in the ocean. Here we present a synthesis about the state of the art for simulating selected trace elements in biogeochemical models: Protactinium, Thorium, Iron and Aluminium. In this contribution we pay particular attention on the role of particles in the cycling of these tracers and how they may provide additional constraints on the transfer of matter in the ocean.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.pocean.2015.01.010
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Evaluating oxygen and oxygen minimum zones in global biogeochemical models (2015)
    In:  [Poster] In: EGU General Assembly 2015, 12.–17.04.2015 , Vienna, Austria .
    Details
    Publication Date: 2019-09-23
    Description: 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.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 7
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    MOPS-1.0: modelling the regulation of the global oceanic nitrogen budget by marine biogeochemical processes (2015)
    Copernicus Publications (EGU)
    In:  Geoscientific Model Development, 8 . pp. 2929-2957.
    Details
    Publication Date: 2019-09-24
    Description: Global models of the oceanic nitrogen cycle are subject to many uncertainties, among them type and form of biogeochemical processes involved in the fixed nitrogen cycle, and the spatial and temporal scales, on which the global nitrogen budget is regulated. We investigate these aspects using a global model of ocean biogeochemistry, that explicitly considers phosphorus and nitrogen, including pelagic denitrification and nitrogen fixation as sink and source terms of fixed nitrogen, respectively. The model explores different parameterizations of organic matter sinking speed, oxidant affinity of oxic and suboxic remineralization, and regulation of nitrogen fixation by temperature and different stoichiometric ratios. Examination of the initial transient behaviour of different model setups initialized from observed tracer distributions reveal changes in simulated nitrogen inventories and fluxes particularly during the first centuries. Millennial timescales have to be resolved in order to bring all biogeochemical and physical processes into a dynamically consistent steady state, for which global patterns of biogeochemical tracers and fluxes are reproduced quite well. Analysis of global properties suggests that particularly particle sinking speed, but also the parameterization of denitrification determines the extent of oxygen minimum zones, global nitrogen fluxes, and hence the oceanic nitrogen inventory. However, the ways and directions, in which different parameterizations of particle sinking, nitrogen fixation and denitrification affect the global diagnostics, are different, suggesting that these may, in principle, be constrained independently from each other. Analysis of the model misfit suggests a particle flux profile close to the one suggested by Martin et al. (1987). Simulated pelagic denitrification best agrees with the lower values between 59 and 84 Tg N yr−1 recently estimated by other authors.
    Type: Article , PeerReviewed
    Format: text
    Format: archive
    DOI: 10.5194/gmd-8-2929-2015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Reviews and syntheses: Parameter identification in marine planktonic ecosystem modelling (2017)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 14 (6). pp. 1647-1701.
    Details
    Publication Date: 2020-02-06
    Description: To describe the underlying processes involved in oceanic plankton dynamics is crucial for the determination of energy and mass flux through an ecosystem and for the estimation of biogeochemical element cycling. Many planktonic ecosystem models were developed to resolve major processes so that flux estimates can be derived from numerical simulations. These results depend on the type and number of parameterizations incorporated as model equations. Furthermore, the values assigned to respective parameters specify a model's solution. Representative model results are those that can explain data; therefore, data assimilation methods are utilized to yield optimal estimates of parameter values while fitting model results to match data. Central difficulties are (1) planktonic ecosystem models are imperfect and (2) data are often too sparse to constrain all model parameters. In this review we explore how problems in parameter identification are approached in marine planktonic ecosystem modelling. We provide background information about model uncertainties and estimation methods, and how these are considered for assessing misfits between observations and model results. We explain differences in evaluating uncertainties in parameter estimation, thereby also discussing issues of parameter identifiability. Aspects of model complexity are addressed and we describe how results from cross-validation studies provide much insight in this respect. Moreover, approaches are discussed that consider time- and space-dependent parameter values. We further discuss the use of dynamical/statistical emulator approaches, and we elucidate issues of parameter identification in global biogeochemical models. Our review discloses many facets of parameter identification, as we found many commonalities between the objectives of different approaches, but scientific insight differed between studies. To learn more from results of planktonic ecosystem models we recommend finding a good balance in the level of sophistication between mechanistic modelling and statistical data assimilation treatment for parameter estimation
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-14-1647-2017
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Evaluation of NorESM-OC (versions 1 and 1.2), the ocean carbon-cycle stand-alone configuration of the Norwegian Earth System Model (NorESM1) (2016)
    Copernicus Publications (EGU)
    In:  Geoscientific Model Development, 9 . pp. 2589-2622.
    Details
    Publication Date: 2019-02-01
    Description: Idealised and hindcast simulations performed with the stand-alone ocean carbon-cycle configuration of the Norwegian Earth System Model (NorESM-OC) are described and evaluated. We present simulation results of two different model versions at different grid resolutions and using two different atmospheric forcing data sets. Model version NorESM-OC1 corresponds to the version that is included in the fully coupled model NorESM-ME1, which participated in CMIP5. The main update between NorESM-OC1 and NorESM-OC1.2 is the addition of two new options for the treatment of sinking particles. We find that using a constant sinking speed, which has been the standard in NorESM's ocean carbon cycle module HAMOCC (HAMburg Ocean Carbon Cycle model) does not transport enough particulate organic carbon (POC) into the deep ocean below approximately 2000 m depth. The two newly implemented parameterisations, a particle aggregation scheme with prognostic sinking speed, and a simpler scheme prescribing a linear increase of sinking speed with depth, provide better agreement with observed POC fluxes. Additionally, reduced deep ocean biases of oxygen and remineralised phosphate indicate a better performance of the new parameterisations. For model version 1.2, a re-tuning of the ecosystem parameterisation has been performed, which (i) reduces previously too high primary production in high latitudes, (ii) consequently improves model results for surface nutrients, and (iii) reduces alkalinity and dissolved inorganic carbon biases at low latitudes. We use hindcast simulations with prescribed observed and constant (pre-industrial) atmospheric CO2 concentrations to derive the past and contemporary ocean carbon sink. For the period 1990–1999 we find an average ocean carbon uptake ranging from 2.01 to 2.58 Pg C yr-1 depending on model version, grid resolution and atmospheric forcing data set.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/gmd-9-2589-2016
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Calibration of a simple and a complex model of global marine biogeochemistry (2017)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 14 . pp. 4965-4984.
    Details
    Publication Date: 2020-02-06
    Description: The assessment of the ocean biota's role in climate climate change is often carried out with global biogeochemical ocean models that contain many components, and involve a high level of parametric uncertainty. Examination the models' fit to climatologies of inorganic tracers, after the models have been spun up to steady state, is a common, but computationally expensive procedure to assess model performance and reliability. Using new tools that have become available for global model assessment and calibration in steady state, this paper examines two different model types – a complex seven-component model (MOPS), and a very simple two-component model (RetroMOPS) – for their fit to dissolved quantities. Before comparing the models, a subset of their biogeochemical parameters has been optimised against annual mean nutrients and oxygen. Both model types fit the observations almost equally well. The simple model, which contains only nutrients and dissolved organic phosphorus (DOP), is sensitive to the parameterisation of DOP production and decay. The spatio-temporal decoupling of nitrogen and oxygen, and processes involved in their uptake and release, renders oxygen and nitrate valuable tracers for model calibration. In addition, the non-conservative nature of these tracers (with respect to their upper boundary condition) introduces the global bias as a useful additional constraint on model parameters. Dissolved organic phosphorous at the surface behaves antagonistically to phosphate, and suggests that observations of this tracer – although difficult to measure – may be an important asset for model calibration
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/bg-14-4965-2017
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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