ICOS Science Conference 2022: Day 3, Session 25

1. Modelling marine carbon cycle in the
Mediterranean Sea under present-day and future
conditions
Gianpiero Cossarini, Paolo Lazzari, Marco Reale, Stefano Salon,
Cosimo Solidoro (and the Med-MFC-BGC team)
ICOS science conference, Utrecht, NL & Online, 13-15 September 2022

2. 2
Objective: how has the increase of atmospheric CO2 changed
the carbon cycle in present-day conditions, and which are the
future projections?
Background: increase of atmospheric CO2 and impact on carbon cycle of the Mediterranean Sea
Artuso et al., 2009
Ocean heat content trend (0-700m) and map of cumulative trend of
temperature in the last 30 years from Marine Copernicus Service
Atmospheric CO2 increase in the last decades and future pathways

3. contents
Ø carbon cycle in biogeochemical models
Ø biogeochemical model used in the Marine Copernicus reanalysis and future
scenario simulations
Ø reanalysis validation
Ø present-day condition of CO2 air-sea exchange and carbon cycle
Ø future scenario simulations and projected changes
Ø conclusions
3

4. 4
Biogeochemical processes included:
(1) air-sea carbon exchange
(2) photosynthesis
(3) Respiration
(4) mortality/excretion (from living to
no-living particulate organic
compartment)
(5) sink of particles (POC and PIC)
(6) mineralization to dissolved
(7) and (8) microbial food web
(exudation, assimilation)
(9) bacterial respiration
(10) external inputs (terrestrial input)
(11) exchanges at the Gibraltar and
Dardanelles Straits
How biogeochemical models describe the marine carbon cycle
2
3
10
11

5. 5
Boundary
Conditions
Atlantic (GLORS-REA
1/4° & clim.) &
Dardanelles (clim.)
Land interface:
runoff and
nutrient loads
39 rivers (GRDC,
UNEP-MAP, Perseus)
Observations
satellite and profiles
of T, S, SLA, SST, and
CHLOROPHYLL
Atmospheric forcing
ECMWF ERA5 (0.25° res, 1 h) momentum, water & heat fluxes
Atmospheric N and P deposition
3DVarBio – data
assimilation
3DVAR – data
assimilation
Marine Copernicus Reanalysis (1999-2020)
Atmospheric CO2
The Mediterranean Sea model: reanalysis for the present
Escudier et al., 2021; Cossarini et al., 2021
BFM
biogeoche
mical
dynamics
NEMO 3.6 @1/24°ocean dynamics

6. 6
Atmospheric forcing
ARPEGE-Climate at 50-km: momentum, water and heat fluxes
CMCC-CM at 0.5° (Scoccimarro etal., 2011)
Atmospheric N and P deposition
2015-2100 future biogeochemical scenarios:
-> SRES A2 (Solidoro et al., 2021)
-> RCP4.5 and RCP8.5 (Reale etal., 2022)
Atmospheric CO2
Boundary
Conditions
Atlantic (GLORS-REA
1/4° & clim.) &
Dardanelles (clim.)
Observations
satellite and profiles
of T, S, SLA, SST, and
CHLOROPHYLL
Land interface:
runoff and
nutrient loads
Ludwig et al.,2009
The Mediterranean Sea model: reanalysis for the present and future scenario simulations
Atmospheric forcing
ECMWF ERA5 (0.25° res, 1 h) momentum, water & heat fluxes
Atmospheric N and P deposition
NEMO 3.6 @1/24°ocean dynamics
3DVarBio – data
assimilation
3DVAR – data
assimilation
BFM
biogeoche
mical
dynamics
BFM
biogeoche
mical
dynamics
NEMOMED8 @1/8° Adloff et al., 2015
NEMO MFS16 @1/16° Lovato et al., 2013

7. 7
Reanalysis validation: how reliable is BFM model to simulate carbonate system variables?
Model surface pCO2 vs SOCAT v2
RMSD = 38ppm
RMSD = 32µmol/kg
Model DIC vs EMODNet2018
ion
nwm
EMODNet2018
model

8. 8
D’ortenzio et al., 2008
Cossarini et al., 2021
sink
source
molC
m-2y-1
Global Carbon Project,
Hauck et al., 2020
Reanalysis carbon cycle: air-sea flux of CO2 and comparison with other estimations
CO2 air-sea flux [TgC/y]
sink
source
sink source
sink
source
3.5

9. 9
Reanalysis carbon cycle: primary production and sink of particulate organic carbon (POC) and particulate
inorganic carbon (PIC)
0.44
sink at 200m [TgC/y]
at 500m
0.38
NPP 268 TgC/y
4.7
net primary production
(map)
biological carbon pump
(contour)
vs
carbonate pump (contour)
0.2
CO2 air-sea flux [TgC/y]
3.5
POC
PIC

10. 10
Reanalysis carbon cycle: external input, circulation and transport at the straits
DIC annual fluxes [TgC/y]
OC 1.1
9.3
Rivers input [TgC/y] Dardanelles Strait
exchange [TgC/y]
Mediterranean Sea
thermohaline
circulation:
-> upper waters
-> dense and deep
waters
-> dense water
formation sites
Figure from Bergamasco and Malamotte, 2001
774
791
CO2 air-sea flux [TgC/y]
DIC flux at the Gibraltar Strait [TgC/y]
10.0
3.5

11. 11
Reanalysis carbon cycle: accumulation of DIC in the water column
+2.7
+23.6
+26.9
+26.4
-11.4
+0.0
+4.8
+4.9
numbers = DIC variation at
end of the reanalysis w.r.t.
initial condition [µmol/kg]
+10.0
-4.8

12. 12
Future scenarios: removing model biases (control and climate scenario simulations)
Anomaly at the end of
the century
(unbiased scenario) =
scenario – control

13. 13
Future scenario results: DIC anomaly ([2090-2099] - present) in the Mediterranean Sea
RCP4.5 and RCP8.5 scenarios
a. warming contrasts solubility pump (-25%), but atm CO2 increase prevails
b. marked accumulation in the eastern sub-basin (vert.arrow)
c. DIC export through LIW (hor. arrow)

14. 14
Future scenario results: impacts on carbon budget and fluxes
C inventory: TgC
Processes: gross primary production
(gpp), community respiration (resp),
airsea flux (fluxCO2), river C input
(river), exchanges at the straits
[TgC/y]
Solidoro et al., 2022
end of 21st century
+400% of atmospheric CO2 sink
+5% DIC concentration (higher
at east)

15. 15
Future scenario results: impacts on carbon budget and fluxes
C inventory: TgC
Processes: gross primary production
(gpp), community respiration (resp),
airsea flux (fluxCO2), river C input
(river), exchanges at the straits
[TgC/y]
Solidoro et al., 2022
end of 21st century
Increase of temperature: +3°C
Increase of metabolism:
respiration increases more than
production

16. 16
Future scenario results: impacts on carbon budget and fluxes
C inventory: TgC
Processes: gross primary production
(gpp), community respiration (resp),
airsea flux (fluxCO2), river C input
(river), exchanges at the straits
[TgC/y]
Solidoro et al., 2022
end of 21st century
Change in the thermohaline
circulation: reversal of the net C
fluxes at the straits;
accumulation of DIC in deeper
layer => pH decreases of about
0.25/0.3

17. conclusions
Ø According to reanalysis (past reconstruction):
-> Mediterranean is a weak sink of atmospheric CO2
-> DIC has been accumulating over the past decades
-> difference in the fate of absorbed carbon between east and west sub-basin
Ø Future scenarios show that:
-> atm CO2 will accumulate from surface toward deeper layers
-> other processes (e.g., change in thermohaline circulation) exacerbate the DIC accumulation
-> as a side effect (not discussed here), pH will decrease of about 0.25/0.3 units

18. Thank you
and a special thank to:
the OGS staff working for the Copernicus Med-MFC
BIO center (follow us on medeaf.inogs.it);
colleagues of the Copernicus Med-MFC PHY from
CMCC (IT);
Tomas Lovato, Simona Masina, Giovanni Galli and
Samuel Somot for collaboration in the future
scenario simulations
18