MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
Furthermore, a new preliminary multiyear product of 2D 
surface current has been available internally since July 
2020, as a demonstration product. This product is inherited 
from ESA GlobCurrent and CNES DUACS-MR projects. The 
method is implemented to enhance the effective spatio- 
temporal resolution of the satellite altimeter-derived 
gridded geostrophic current. It uses high resolution satellite 
images of ocean tracers (e.g., sea surface temperature, SST) 
which relates to ocean surface dynamics. The approach is 
based on the inversion of the heat conservation equation for 
horizontal velocities using altimeter geostrophic velocities 
as background and prescribing source and sinks terms a 
prior! values and associated errors from successive SST 
fields (Rio and Santoleri, 2018). The product is provided at 
1/10° horizontal resolution along the 1993-2018 period. 
1.5 CMEMS-FFNN Surface Carbon 
A new surface carbon multiyear product, including air-sea 
flux of CO, (fgco2), partial pressure of CO, (spco2) and pH has 
been available since April 2019. The model called CMEMS 
=FNN is inherited from the EU H2020 AtlantOS project and is 
developed by LSCE. It relies on the implementation of feed- 
forward neural network models (FFNN) for the interpolation 
of sparse carbon system measurements to basin-wide maps 
on a 1° horizontal resolution grid at a monthly period (Denvil- 
Sommer et al., 2019). This method establishes non-linear 
relationships between chosen drivers or predictors such as 
5ST, SSS, Chlorophyll, mixed layer depth, surface height, 
pCO, climatology and surface ocean pCO, measurements 
from SOCAT (https://www.socat.info/). Reconstructec 
variables (fgco2, spco2, pH) are distributed with associatec 
uncertainties derived from the 100-member CMEMS-FFNN 
ansemble. Related OMIs for ocean carbon sink (ie., globa 
vearly integrated air-sea flux of CO,) and ocean acidification 
{je., global mean sea water pH) are also available. The latter 
was published in issue 4 of Copernicus Marine Service 
Ocean State Report (Gehlen et al., 2020). 
Three versions of the product have been successively 
released. For its 1° publication in April 2019, the MY 
timeseries and the ocean acidification OMI covered the 
2001-2017 period. The 2"* publication in April 2020 
included a new version of the ensemble based FFNN and 
a timeseries covering the 1985-2018 period together with 
the two OMls. The timeseries (product and OMlIs) was 
‘urther extended in December 2020 to cover the 1985 
2019 period. 
CMEMS-FFNN air-sea CO, flux product have been 
zontributing since 2019 to the yearly assessment of the 
5lobal Carbon Budget (Friedlingstein et al., 2020; Hauck 
at al., 2020). The combination of spco2 and surface ocear 
alkalinity allows to reconstructing surface ocean pH from 
'985 onward. The global ocean surface pH is decreasing 
‚Figure 3), as a direct consequence of the uptake by the 
acean of carbon dioxide emitted by human activities such 
as e.g., fossil fuel burning and land-use change. 
Yearly mean surface sea water pH reported on total scale 
3.12 
8.11 
Datatype : Single product ; 
Credit : E.U. Copernicus Marine Service Information ; 
>> Copemicus 
Su Marine Service 
8.10. 
_. 8.09 
> 8.08 
8.07 
| 
8.06 
8.05 
8.04 - 
Ga 
1985-2019 trend: 
© —0.0016 + 0.0006 yr-} 
A 
zuropearn 
Commission 
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MERCATOR 
OCEAN 
INTERNATIONAI 
WaRr 
iRure 3: Yearly mean surface sea water pH reported on total scale.