Abstract
Abstract. Ecosystem models are often assessed using quantitative metrics of absolute ecosystem state, but these model–data comparisons are disproportionately vulnerable to discrepancies in the location of important circulation features. An alternative method is to demonstrate the models capacity to represent ecosystem function; the emergence of a coherent natural relationship in a simulation indicates that the model may have an appropriate representation of the ecosystem functions that lead to the emergent relationship. Furthermore, as emergent properties are large-scale properties of the system, model validation with emergent properties is possible even when there is very little or no appropriate data for the region under study, or when the hydrodynamic component of the model differs significantly from that observed in nature at the same location and time.A selection of published meta-analyses are used to establish the validity of a complex marine ecosystem model and to demonstrate the power of validation with emergent properties. These relationships include the phytoplankton community structure, the ratio of carbon to chlorophyll in phytoplankton and particulate organic matter, the ratio of particulate organic carbon to particulate organic nitrogen and the stoichiometric balance of the ecosystem.These metrics can also inform aspects of the marine ecosystem model not available from traditional quantitative and qualitative methods. For instance, these emergent properties can be used to validate the design decisions of the model, such as the range of phytoplankton functional types and their behaviour, the stoichiometric flexibility with regards to each nutrient, and the choice of fixed or variable carbon to nitrogen ratios.
Highlights
Numerical models of the environment are used frequently for informing policy decisions, for forecasting the impact of climate change, and to obtain a deeper understanding of nature
There is a long history of works that demonstrate model validation using static fields, spatial distributions and dynamic variability, including Droop (1973), Fasham et al (1990), Taylor (2001), Blackford (2004), Allen et al (2007), Jolliff et al (2009), Shutler et al (2011), Saux Picart et al (2012), de Mora et al (2013), and Kwiatkowski et al (2014)
All six biogeochemical models were required to use identical model parameters and settings to run the physical component of the simulation, Nucleus for European Modelling of the Ocean (NEMO)
Summary
Numerical models of the environment are used frequently for informing policy decisions, for forecasting the impact of climate change, and to obtain a deeper understanding of nature. As a solution to the problem of the absence of data and presence of poorly constrained physics, Holt et al (2014) wrote “there is a need for metrics that assess the fidelity of the biogeochemical processes independently of the physics” In that work, they identify one such functional relationship: the link between diatom chlorophyll and total community chlorophyll. The relationship observed in Holt et al (2014) was a widespread general response in all the plankton models that was independent of local hydrodynamic conditions This relationship is a largescale property of the marine ecosystem, and is expected to hold true even in regions with few historical measurements.
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