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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-2018-491
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-491
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 18 Dec 2018

Research article | 18 Dec 2018

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

Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing

Ulrike Löptien1,2 and Heiner Dietze1,2 Ulrike Löptien and Heiner Dietze
  • 1Institute for Geosciences, University of Kiel, Ludewig-Meyn-Str. 10, 24118 Kiel, Germany
  • 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany

Abstract. Anthropogenic emissions of greenhouse gases such as CO2 and N2O impinge on the earth system which, in turn, modulates atmospheric greenhouse gas concentrations. The underlying feedback mechanisms are complex and, at times, counterintuitive. So-called Earth System Models have recently matured to standard tools tailored to assess these feedback mechanisms in a warming world. Respective model applications range from being targeted at basic process understanding to the assessment of geo-engineering options. A problem endemic to all these applications is the need to estimate poorly known model parameters, specifically for the biogeochemical component, based on observational data (e.g. nutrient fields). In the present study, we illustrate that by such an approach biases in the physical ocean-circulation model component of an Earth System Model can reciprocally compensate biases in the pelagic biogeochemical model component (and vice versa). We present two configurations of an Earth System Model that share a remarkably similar steady state (based on ad-hoc measures) when driven by historical boundary conditions, even though they feature substantially different configurations (sets) of ocean-mixing and biogeochemical cycling (model parameters). When projected into the future the similarity between the model responses breaks. Metrics like total oceanic carbon content and suboxic volume diverge in the model configurations as the Earth warms. Our results reiterate that advancing the understanding of oceanic mixing processes will reduce the uncertainty of future projections of the oceanic biogeochemical cycles. Vice versa, we suggest that an advanced understanding of oceanic biogeochemical cycles can be used for advancements in the ocean circulation modules.

Ulrike Löptien and Heiner Dietze
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Ulrike Löptien and Heiner Dietze
Ulrike Löptien and Heiner Dietze
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Short summary
Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth System Models provide a base for related political decision making. One challenge is to arrive at reliable model parameter estimates for the ocean biogeochemistry module. We illustrate pitfalls where flaws in the ocean module are masked by wrongly tuning the biogeochemistry and discuss ensuing uncertainties in climate projections.
Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth...
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