van Leeuwen et al. 
eutrophic values for indicators of eutrophication across vast marine 
zegions, while keeping a focus on local ecosystem functioning and 
on the continuity of transboundary processes. 
? Methcas 
2.1 Ensemble method overview 
Eight modelling centres participated in the ensemble modelling 
exercise. To ensure comparable results between the different models 
.n the ensemble, some harmonized model inputs were prescribed in 
a joint protocol. These included all external sources of nutrients: 
:iverine nutrient loads, atmospheric deposition and boundary 
conditions. S imulation period and model output variables were 
also prescribed. Meteorological forcing was not prescribed, to allow 
the participants to use the same forcings as applied in published 
validation results. Each partner also used its standard bathymetry, 
‚or the same reason. Boundary conditions were taken from a shared 
source. All partners were asked to submit results for 2009-2014 (the 
COMP3 assessment period) for variables aligned with the 
eutrophication assessment protocol by OSPAR: Dissolved 
Inorganic Nitrogen (DIN, surface layer), Dissolved Inorganic 
Phosphorus (DIP, surface layer), Total Nitrogen (TN, depth- 
averaged), Total Phosphorous (TP, depth-averaged) and the 
nitrogen to phosphorus (N:P, depth-averaged) ratio for the winter 
period (December-February). Chlorophyll (Chl, surface layer), 
chlorophyll 90’ percentile (Chl P90, surface layer) and light 
attenuation (Ky, surface layer) were averaged over the growing 
season (March-September), while near-bed oxygen levels (O,, near- 
bed layer) and net primary production (netPP, depth-integrated) 
were considered over the whole year. Models with no benthic 
compartment applied a three-year spin up period to move from 
10.3389/fmars.2023.1129951 
initial conditions. Models with a benthic compartment capable of 
nutrient storage applied a longer, suitable spin up period for the 
historic scenario to arrive at an equilibrium between benthic 
nutrients and the applied nutrient inputs. 
The participating modelling centres were: the Cefas (Centre for 
Fisheries and Aquaculture Science, Lowestoft, UK), Deltares 
(Netherlands), IFREMER (L’Institut Francais de Recherche pour 
V’Exploitation de la Mer, France), JRC (Joint Research Centre in 
[spra, Italy but representing the EU), the University of Oldenburg 
(Oldenburg, Germany), RBINS (Royal Belgian Institute of Natural 
Sciences, Belgium), SMHI (Swedish Meteorological and 
Hydrological Institute, Sweden), and the University of Hamburg 
together with the Helmholtz Zentrum Geesthacht (now called 
Hereon) (UHH-HZG, Germany). A detailed overview of the 
different models is provided in Appendix D (descriptions, 
Supplementary Materials) and E (table overview, Supplementary 
Materials). Both large domain models (covering the entire 
Northwest European shelf) and small domain models (covering 
2.g. only the English Channel or the Southern North Sea) were 
applied to the exercise. 
The different models have varying degrees of complexity with 
respect to the processes they represent. Not all use the same external 
nutrient inputs (Table 1) or have the same number of plankton 
functional groups (Appendix E; Supplementary Table 2). Besides 
internal model differences the simulations used in this exercise also 
differ in spatial resolution (Appendix E; Supplementary Table 2) 
and coverage (Figure 1). Only the SMHI model domain includes the 
“ull Baltic Sea, all other domains have an open boundary with the 
Baltic in the Belt Sea region. Table 1 shows the nutrients that are 
used as inputs in the different models. Note that even if a model 
does not use input for a certain nutrient, the dynamics of this 
nutrient are usually still part of the model’s internal dynamics 
(Appendix E; Supplementary Table 2). 
TABLE 1 Overview of the nutrients used by each model from the supplied riverine inpı.* 
MIRO&CO | RBINS (BE) 
MARS3D- 
Ifremer (FR) 
MANGA4 
X 
X: 
Uni-Hamburg 
ECOHAM 
/HZG (DE) 
GPM | Uni-Oldenburg 
(DE) 
DFLOW-FW Deltares (NL) 
GETM-JRC- 
) JRC (ZU) 
ERSEM 
GETM-ERSEM- 
Cefas (UK) l 
BFM 
NEMO-SCOBI SMHI (SE) | x 
BY) mm 
Aere “Uni” stands for “University of”. Q stands for fresh water discharge 
"rontiers in Marine 1cience 
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