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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-122
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-122
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Apr 2019

Research article | 10 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

The effect of marine aggregate parameterisations on global biogeochemical model performance

Daniela Niemeyer, Iris Kriest, and Andreas Oschlies Daniela Niemeyer et al.
  • Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany

Abstract. Particle aggregation determines the particle flux length scale, possibly the marine oxygen concentration and thus affecting the volume of oxygen minimum zones (OMZs) that are of special relevance for ocean nutrient cycles and marine ecosystems, and that have been found to expand faster than can be explained by current state-of-the-art models. To investigate the impact of particle aggregation on global model performance, we carried out a sensitivity study with different parameterisations of marine aggregates and two different model resolutions. Model performance was investigated with respect to global nutrient and oxygen concentrations, as well as extent and location of OMZs. Results show that including an aggregation model improves the representation of OMZs. Moreover, we found that besides a fine spatial resolution of the model grid, the consideration of porous particles, an intermediate to high particle sinking speed and a moderate to high stickiness improve the model fit to both, global distributions of dissolved inorganic tracers and regional patterns of OMZs, compared to a model without aggregation. Our model results therefore suggest that improvements not only in the model physics, but also in the description of particle aggregation processes can play a substantial role in improving the representation of dissolved inorganic tracers and OMZs on a global scale. However, dissolved inorganic tracers are apparently not sufficient for a global model calibration, which could necessitate global model calibration against a global observational dataset of marine organic particles.

Daniela Niemeyer et al.
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Daniela Niemeyer et al.
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Short summary
Recent studies suggest spatial variations of the marine particle flux length scale. Using a global biogeochemical ocean model, we investigate if changes in particle size and size-dependent sinking can explain this variation. We address uncertainties by varying aggregate properties and circulation. Both aspects have an impact on the representation of nutrients, oxygen and oxygen minimum zones. The formation and sinking of large aggregates in productive areas lead to deeper flux penetration.
Recent studies suggest spatial variations of the marine particle flux length scale. Using a...
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