Presented at the 3rd ICOS Science Conference in Prague, Czech Republic, 11-13 Sep 2018.

1. ANOMALOUS SEA-AIR CO2 FLUX IN THE NORTH
TROPICAL ATLANTIC DURING 2010 EVIDENCED BY
MODELLING AND OBSERVATIONS
1 LOCEAN, Sorbonne Univ.-IRD-CNRS-MNHN, Paris, FRANCE
2 Univ. Fed. Pernambuco, Recife, BRAZIL
3IRD Centre de Bretagne, Plouzané, FRANCE
4 Trinity College, Dublin, IRELAND
5Instituto de Investigacións Mariñas, CSIC, Vigo, SPAIN
Nathalie Lefèvre1, Doris Veleda2, Pedro Tyaquiçã2, Denis Diverrès3,
J. Severino P. Ibánhez4,5

2. JAN FEB MAR
APR MAY JUN
JUL AUG SEP
OCT NOV DEC
CO2 MONITORING IN THE TROPICAL ATLANTIC
ICOS station:
France-Brazil line
2006-now: France-French Guiana (MN Colibri)
2008-now: France-Brazil (Monte Olivia 2008-2009, Rio Blanco 2009-
2011, Santa Cruz 2012-2014, Cap San Lorenzo 2014-present)
2008
2009
2010
2011
France-Brazil line:
Anomalies of fCO2 from
February to May 2010
CO2 system (from G.O.) on
the France-Brazil line
TSG
Wet box
Dry box

3. Lefèvre et al., JGR 2013
ANOMALIES IN THE NORTH TROPICAL ATLANTIC IN 2010
Strong latent
heat loss
S
N
Equator
Spring, normal year
Heavy rain
Low salinity
E
Spring 2010
S
N
Equator E
SST anomaly
SSS anomaly
ITCZ
ITCZ • Anomaly of ITCZ
position in Spring
2010
• Higher SSS south of
the equator leading
to higher fCO2

4. ANOMALIES IN THE NORTH TROPICAL ATLANTIC IN 2010
SST anomalies of 2010 calculated from the climatology NOAA optimum
Interpolation SST, 0.25o, 1994-2013 (Ibánhez et al., Sci. Rep. 2017)
Warm event in the tropical and subtropical North Atlantic during boreal Spring 2010: sink of
CO2 becomes source of CO2 from Feb to May, 0-30oN, 62-10oW (Ibánhez et al., 2017)
Impact of these SST
anomalies in 2010 at
basin scale?

5. MODEL SIMULATIONS FOR 2010
Mercator-Ocean simulations:
- NEMO modelling platform (Nucleus for European Modelling of the Ocean), global ocean,
1997-2014, spatial resolution of 0.25o
- Biogeochemical component PISCES (Aumont et al., 2015) coupled offline at a daily frequency
- Initial conditions:
- Levitus climatology of 1998 for temperature and salinity,
- World Ocean Atlas 2001 for nutrients (Conkright et al., 2002),
- GLODAPv1 for alkalinity (TA) and Dissolved Inorganic Carbon (DIC) (Key et al, 2005)
- Daily outputs from 2006 to 2014, focus on the region 0-30oN, 70oW-15oW
Objective: detect the anomalies of 2010 in a model to be able to estimate the sea-air CO2 flux at
basin scale (0-30oN)

6. MODEL-DATA COMPARISON FOR 2010
SST 2010 Rio Blanco
SSS 2010 Colibri
fCO2 2010 Rio Blanco
Rio Blanco
(13 voyages)
Colibri
(8 voyages)
Mercator-Ocean MODEL:
- Model simulations and observations
collocated for each cruise
- fCO2=f(TA,DIC)
- Daily outputs from 2006 to 2014

7. 2010 ANOMALIES IN THE MODEL (SST & fCO2)
2010 SST anomalies calculated over 2006-2014 2010 fCO2 anomalies calculated over 2006-2014

8. 2010 ANOMALIES IN THE MODEL (DIC & fCO2)
2010 fCO2 anomalies calculated over 2006-20142010 DIC anomalies calculated over 2006-2014
The DIC anomalies do not contribute to the fCO2 anomalies

9. ANOMALIES IN THE AFRICAN UPWELLING
• Overall, warm anomalies -> positive fCO2 anomalies
• African upwelling:
warm anomalies -> negative fCO2 and DIC anomalies
Subsurface water richer in CO2
In 2010: reduced NE trade winds
-> shallower waters upwelled
-> reduced carbon content in surface waters
-> negative DIC and hence fCO2 anomalies
(correlation DICA-fCO2A of 0.90)
Zoom in April 2010

10. CONCLUSIONS - IMPACT ON THE SEA-AIR CO2 FLUX IN 2010
• Feb-May 2010: sink of CO2 -> source of CO2
• Weaker winds in Spring 2010
• Outgassing of 46.2 TgC yr-1 in 2010 compared
to a mean of 23.3 TgC yr-1 over 2006-2014
(Surface area: 1.7 107 km2)
• fCO2 anomalies of 2010 mostly driven by the
SST anomalies
• CO2 monitoring by merchant ships helped in
detecting the CO2 anomalies of 2010
Anomalies of CO2 in Spring 2010
affect the annual budget at basin scale
North tropical Atlantic 0-30oN, 70oW-15oW