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  • 11
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    Parameterisation of fish variability effects on biogeochemistry through zooplankton mortality: A sensitivity study for the Eastern Tropical South Pacific (2021)
    Details
    Publication Date: 2022-09-13
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: other
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    OceanRep: Poster
  • 12
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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
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    Format: video
    Format: video
    DOI: 10.1038/ngeo3042
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 13
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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
  • 14
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    A novel estimate of ocean oxygen utilisation points to a reduced rate of respiration in the ocean interior (2013)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 10 (11). pp. 7723-7738.
    Details
    Publication Date: 2019-09-23
    Description: The Apparent Oxygen Utilisation (AOU) is a classical measure of the amount of oxygen respired in the ocean's interior. We show that AOU systematically overestimates True Oxygen Utilisation (TOU) in 6 coupled circulation-biogeochemical ocean models. This is due to atmosphere–ocean oxygen disequilibria in the subduction regions, consistent with previous work. We develop a simple, new, observationally-based approach which we call Evaluated Oxygen Utilisation (EOU). In this approach, we take into account the impact of the upper ocean oxygen disequilibria into the interior, considering that transport takes place predominantly along isopycnal surfaces. The EOU approximates the TOU with less than half of the bias of AOU in all 6 models despite large differences in the physical and biological components of the models. Applying the EOU approach to a global observational dataset yields an oxygen consumption rate 25% lower than that derived from AOU-based estimates, for a given ventilation rate.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-10-7723-2013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 15
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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
  • 16
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    Swept under the carpet: organic matter burial decreases global ocean biogeochemical model sensitivity to remineralization length scale (2013)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 10 . pp. 8401-8422.
    Details
    Publication Date: 2019-09-23
    Description: Although of substantial importance for marine tracer distributions and eventually global carbon, oxygen, and nitrogen fluxes, the interaction between sinking and remineralization of organic matter, benthic fluxes and burial is not always represented consistently in global biogeochemical models. We here aim to investigate the relationships between these processes with a suite of global biogeochemical models, each simulated over millennia, and compared against observed distributions of pelagic tracers and benthic and pelagic fluxes. We concentrate on the representation of sediment–water interactions in common numerical models, and investigate their potential impact on simulated global sediment–water fluxes and nutrient and oxygen distributions. We find that model configurations with benthic burial simulate global oxygen well over a wide range of possible sinking flux parameterizations, making the model more robust with regard to uncertainties about the remineralization length scale. On a global scale, burial mostly affects oxygen in the meso- to bathypelagic zone. While all model types show an almost identical fit to observed pelagic particle flux, and the same sensitivity to particle sinking speed, comparison to observational estimates of benthic fluxes reveals a more complex pattern, but definite interpretation is not straightforward because of heterogeneous data distribution and methodology. Still, evaluating model results against observed pelagic and benthic fluxes of organic matter can complement model assessments based on more traditional tracers such as nutrients or oxygen. Based on a combined metric of dissolved tracers and biogeochemical fluxes, we here identify two model descriptions of burial as suitable candidates for further experiments and eventual model refinements.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.5194/bg-10-8401-2013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 17
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    Towards an assessment of simple global marine biogeochemical models of different complexity (2010)
    Elsevier
    In:  Progress in Oceanography, 86 (3-4). pp. 337-360.
    Details
    Publication Date: 2019-09-23
    Description: We present a suite of experiments with a hierarchy of biogeochemical models of increasing complexity coupled to an offline global ocean circulation model based on the “transport matrix method”. Biogeochemical model structures range from simple nutrient models to more complex nutrient-phytoplankton–zooplankton-detritus-DOP models. The models’ skill is assessed by various misfit functions with respect to observed phosphate and oxygen distributions. While there is generally good agreement between the different metrics employed, an exception is a cost function based on the relative model-data misfit. We show that alterations in parameters and/or structure of the models – especially those that change particle export or remineralization profile – affect subsurface and mesopelagic phosphate and oxygen, particularly in the upwelling regions. Visual inspection of simulated biogeochemical tracer distributions as well as the evaluation of different cost functions suggest that increasing complexity of untuned, unoptimized models, simulated with parameters commonly used in large-scale model studies does not necessarily improve performance. Instead, variations in individual model parameters may be of equal, if not greater, importance.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.pocean.2010.05.002
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 18
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    Different parameterizations of marine snow in a 1D-model and their influence on representation of marine snow, nitrogen budget and sedimentation (2002)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 49 (12). pp. 2133-2162.
    Details
    Publication Date: 2016-10-28
    Description: Amodel is presented that simulates the formation of marine aggregates from particles of different origin inside amodel of pelagic biological processes. Experiments are carried out with parameterizations appropriate for different types of aggregates, using different kinds of physical forcing, and compared to observations of dissolved inorganic nitrogen (DIN), particulate organic nitrogen (PON), marinesnow concentration, and sedimentation. The occurrence of large, macroscopically visible aggregates (marinesnow) can best be simulated with parameterizations that have been derived from in situ observations of marinesnow, but not with aparameterization sufficient for dense particles. The parameterization strongly determines the amount and timing of deep export, as well as the post-bloom development of the food web in the upper layers. Detritus in aggregates plays a role mainly during times when zooplankton are abundant, as e.g. in the western Arabian Sea during Southwest Monsoon. Then the large aggregates as fast sinking vehicles may remove detritus quickly from shallow and mid-water depth, preventing the accumulation of nutrients that are produced via detritus decomposition. In this region, detritus contributes strongly to deep sedimentation. The nitrogenbudget at this location with regard to the observations cannot be closed: depending on model type, either the model simulates too high sedimentation, or too high DIN. Possible causes for this mismatch include undercollection by sediment traps, inaccurate representation of physical processes in the model and the neglect of biological processes, such as production of dissolved organic matter or denitrification.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0637(02)00127-9
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 19
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    Sensitivity analysis of simple global marine biogeochemical models (2012)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 26 . GB2029.
    Details
    Publication Date: 2019-09-23
    Description: This study presents results from 46 sensitivity experiments carried out with three structurally simple (2, 3, and 6 biogeochemical state variables, respectively) models of production, export and remineralization of organic phosphorus, coupled to a global ocean circulation model and integrated for 3000 years each. The models’ skill is assessed via different misfit functions with respect to the observed global distributions of phosphate and oxygen. Across the different models, the global root-mean square misfit with respect to observed phosphate and oxygen distributions is found to be particularly sensitive to changes in the remineralization length scale, and also to changes in simulated primary production. For this metric, changes in the production and decay of dissolved organic phosphorus as well as in zooplankton parameters are of lesser importance. For a misfit function accounting for the misfit of upper-ocean tracers, however, production parameters and organic phosphorus dynamics play a larger role. Regional misfit patterns are investigated as indicators of potential model deficiencies, such as missing iron limitation, or deficiencies in the sinking and remineralization length scales. In particular, the gradient between phosphate concentrations in the northern North Pacific and the northern North Atlantic is controlled predominantly by the biogeochemical model parameters related to particle flux. For the combined 46 sensitivity experiments performed here, the global misfit to observed oxygen and phosphate distributions shows no clear relation to either simulated global primary or export production for either misfit metric employed. However, a relatively tight relationship that is very similar for the different model of different structural complexity is found between the model-data misfit in oxygen and phosphate distributions to simulated meso- and bathypelagic particle flux. Best agreement with the observed tracer distributions is obtained for simulated particle fluxes that agree most closely with sediment trap data for a nominal depth of about 1000 m, or deeper.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2011GB004072
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 20
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    A biogeochemical model assessment platform (2014)
    In:  [Poster] In: WGOMD Workshop on High Resolution Ocean Climate Modeling, 07.-09.04.2014, Kiel, Germany .
    Details
    Publication Date: 2014-12-09
    Description: 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.
    Type: Conference or Workshop Item , NonPeerReviewed
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