MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
Since 201 5,the biogeochemical component was continuously 
ımproved (Figure 1). The BFM was improved by: 
revising nutrient formulations of phytoplankton 
(Lazzari et al., 2016), 
-including the carbonate system (Cossarini et al., 2015), 
upgrading the optical component with a new Kd 
dataset and the day-night cycle in photosynthesis 
formulation (Salon et al., 2019; Feudale et al., 2021). 
The O0GSTM transport model improvements included a 
new parallel implementation and the parameterization 
of z* level formulation (Salon et al., 2019). Regarding 
the 3DVarBio data assimilation scheme, developments 
consisted In: 
- assimilation of coastal data (Teruzzi et al., 2018), 
scheme parallelization, 
upgrade for multiplatform satellite and BGC-Argo 
profiles assimilation (Cossarini et al., 2019). 
The off-line coupling between the physical component and 
the MedBFM guarantees the full alignment in terms of 
bathymetry, horizontal and vertical resolution (ie., 1/24° 
and 141 vertical levels since 2017 version), the consistency 
of open boundaries (i.e., Atlantic and Dardanelles) and land 
forcing (Le, 39 rivers since 2017 version). As a result of 
continuous developments, the quality of BIO products has 
significantly improved over the MyOcean and Copernicus 
' period. Indeed, timeseries of the RMSD of the first 
forecast day (Figure 3) shows the decrease of the error of 
Chlorophyll due to some relevant system developments. 
Other mentioned improvements, not visible on Figure 3, 
are fully accounted in the thorough validation framework 
implemented on the regional validation website (Salon 
et al., 2019) and the latest version of the NRT Copernicus 
Marine Service documentation (Feudale et al., 2021). 
BFM: day/night 
, ) BFMv5 # . 8 
DA: Sat CHL DA: coastal CHL N/P formulation DA: BGC- Argo 
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‚igure 3: Timeseries of the RMSD of the first day of forecast of Chlorophyll computed after the weekly analysis run (blue solid line). Statistics 
nave been computed pre-operationally in 2011-2012 and operationally since January 2013. Timings of changes in horizontal resolution 
(green) and in biogeochemical model and data assimilation (red) are indicated in the upper Dart of the chart 
During the 6 years of the Copernicus Marine Service 
program, two biogeochemical reanalyses have been 
produced integrating improvements and developments 
from the NRT Mediterranean Sea model systems. From the 
first (2015) tothe latest (2021) one,the major improvements 
of the setup include: 
the increase of resolution from 1/16° to 1/24° and 
from 71 to 125 vertical levels. 
- the update of the atmospheric (e.g., ERA5) and land (e.g., 
nutrient loads from Perseus FP7 project) forcing and 
boundary (e.g., WOA2018 for the Atlantic boundary), 
- the update of initial conditions (e.g., Emodnet 2018) 
The 2021 biogeochemical reanalysis provides CMEMS with 
a 1999-2020 timeseries of 12 validated variables (NO,, PO,, 
NH,, Chl, PhytoC, ZooC, npp, oxygen, Alk, DIC, pH, pCO,, air 
sea CO. flux)