Variability of the parameters
of the CO2 system in the
continental shelf of Ceará
Andréa Carvalho, Nathalie Lefèvre, Rozane Marins, Roseline Torres
The global carbon budget
Sources and Sinks
Climatology of Takahashi et al., 2009
Processes affecting CO2 in the ocean
www.pmel.noaa.gov
Processes
Impact on fCO2
Warming
Increase of 4%/oC (thermodynamical relationship)
Increase of salinity
Increase of fCO2
Chlorophyll production
Decrease of fCO2 (photosynthesis)
Upwelling
Increase of surface fCO2
The coastal ocean: a source or a sink
for atmospheric CO2?
• Impact of rivers (Amazon): large blooms of diatoms
create CO2 drawdowns
SOURCE OF CO2
ATM
SINK OF CO2
Lefèvre et al., 2010
Jaguaribe River
Objectives
• Generate the first field measurements of the CO2
parameters for the region;
• Describe the surface distribution of the carbon properties;
• Understand the processes (physical/biological) that
influcence the CO2 distribution in the sea surface and;
• Determine the air-sea flux of CO2 during the dry season.
The Cruise
BRAZIL
Measurements:
•Physical Parameters (CTD, Thermosal)
•CO2 parameters (TCO2,TA,pCO2)
•Chlorophyll a
•Dissolved Oxygen
Spatial Distribution of pCO2
SST= 26.73 ±0.14
SSS= 36.46± 0.21
TCO2 and TA
TA= 2397.7 ±5.3 µmol.Kg-1
TCO2= 2059.2 ±4.6 µmol.Kg-1
2075,0
TA=f(S)
2450
2070,0
Core…
2440
2065,0
2420
2055,0
TA
TCO2
2430
2060,0
2410
2050,0
2400
y = 0,6341x + 538,9
R² = 0,5685
2045,0
2040,0
2380,0
2390,0
2400,0
TA
2410,0
2390
2380
36
36,2
36,4
36,6
Salinity
36,8
37
Chlorophyll a
Method of Jeffrey and Humphrey (1975)
Mean Chlorophyll= 0.09 ± 0.09µg.L-1
Dissolved Oxygen
• Winkler 1888
Mean DO = 6.5 ± 0.15 mg.L-1
Air – sea flux of CO2
F = k(wind).Ko.(T, S).(fCO2 sea – fCO2 air)
F > 0  SOURCE
k= 0.27 wsp2 (Sc/660)-0.5
F < 0  SINK
Ko = Solubility of CO2 (Weiss, 1974)
Measurements:
Mean fCO2 sea= 401.6±8.6 µatm
Mean fCO2 air= 375.8 µatm
Mean Flux of CO2 to the atmosphere= 3.53 ±1.15 mmol.m-2.day-1
Conclusions
• Predominance of physical processes over biological
processes;
• A source of CO2 to the atmosphere in October
2012;
• Mean Flux CO2= 3.53 ±1.15 mmol.m-2.day-1 and;
• No riverine influence observed during this season.
And Perspectives
Determine the seasonal variability (measurements during
the wet season).
Special thanks
• ECMWF ERA-Interim wind data from the ECMWF data server
• The service national SNAPO-CO2 (LOCEAN, Paris) for the analyses
of dissolved inorganic carbon and total alkalinity.
Acknowledgements
ANEXOS
Parameters of the CO2 system
4 parameters: fCO2, DIC, TA and pH
pCO2 and fCO2 : non ideal gas
DIC = [CO2]* + [CO32-] + [HCO3-] µmol kg-1
TA: bicarbonate (HCO3-) and carbonate (CO3--) µmol. Kg-1
pH: monitoring acidification
Knowing 2 parameters we can calculate the other two:
pH
TA
DIC
fCO2
pH, TA
-
-
± 3.8
± 2.1
pH, DIC
-
± 2.7
-
± 1.8
TA, DIC
± 0.0062
-
-
± 5.8
TA, fCO2 ± 0.0021
-
± 3.4
-
DIC,
fCO2
± 0.0023
± 3.0
-
-
fCO2, pH
-
± 18
± 15
-
Errors made on the
calculation of the carbon
parameters from the
measurements of two of
them
(Millero, 1995; Zeebe and
Wolf-Gladrow,2007)
• Seawater samples were taken for surface
analysis chlorophyll a according to Jefrey and
Humphey 1970
• inorganic carbon (TCO2) and total alkalinity
(TA) using potenctiometric titration derived
from the method developed by Edmond
(Edmond, 1970) with a closed cell.
2075,0
2070,0
2065,0
DIC
DICx TA
2060,0
2055,0
2050,0
2045,0
2040,0
2380,0
2385,0
2390,0
2395,0
TA
2400,0
2405,0
TA=f(S)
2450
Corenav 3
2440
2430
SSS x TA
TA
2420
2410
2400
2390
2380
36
36,2
36,4
36,6
Salinity
36,8
37
2410,0
The CO2 System
Successive measurements:
• CO2 standards
• Seawater
• Atm air
• Repeat cycle: standards…
CO2 standards (air with
known CO2 concentration:
280 ppm, 360 ppm, 500 ppm)
• The partial pressures of CO2 (pCO2 ) for the
ocean and atmosphere were measured underway
during the cruise by an infrared CO2/H2O
detector Li-Cor model 7000 as described by
Dickson et al. 2007 .
French system on board the Corenav 3, Oct. 2012
Building of a CO2 system in Brazil  ongoing at INPE
Air sea flux
• The net sea-air CO2 fluxes (F, mmol m-2 d-1) is
calculated using : F= k K0 (fCO2sw- fCO2air)
• K0 is the solubility of CO2 as a function of SST
and SSS (Weiss, 1974). The gas transfer velocity
for CO2(k) was calculated according to Sweeney
et al. (2007): k=0.27 wsp2(Sc/660)-0.5 .
• Sc is the Schmidt number and 660 is the
Schmidt number of CO2 in seawater at 20°C
(Wanninkhof, 1992) and wsp is the Wind speed
at 10m.
• DIC
• TA
DIC
TA