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

Climatology of Takahashi et al., 2009

Sources and Sinks

Processes affecting CO2 in the ocean

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

www.pmel.noaa.gov 

• Impact of rivers (Amazon): large blooms of

diatoms create CO2 drawdownsATM

SOURCE OF CO2

SINK OF CO2

Lefèvre et al., 2010

The coastal ocean: a source or a sink for atmospheric CO2?

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

Measurements:•Physical Parameters (CTD, Thermosal)•CO2 parameters (TCO2,TA,pCO2)•Chlorophyll a•Dissolved Oxygen

BRAZIL

Spatial Distribution of pCO2

SST= 26.73 ±0.14 SSS= 36.46± 0.21

TCO2 and TA

TCO2= 2059.2 ±4.6 µmol.Kg-1 TA= 2397.7 ±5.3 µmol.Kg-1

2380.0 2385.0 2390.0 2395.0 2400.0 2405.0 2410.0 2415.02030.0

2035.0

2040.0

2045.0

2050.0

2055.0

2060.0

2065.0

2070.0

2075.0

TA

TCO2

36 36.2 36.4 36.6 36.8 372380

2390

2400

2410

2420

2430

2440

2450TA=f(S)

C...

Salinity

TA

y = 0,6341x + 538,9R² = 0,5685

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

Measurements:

Mean fCO2 sea= 401.6±8.6 µatm

Mean fCO2 air= 375.8 µatm

F = k(wind).Ko.(T, S).(fCO2 sea – fCO2 air)

F > 0 SOURCE

F < 0 SINK

k= 0.27 wsp2 (Sc/660)-0.5

Ko = Solubility of CO2 (Weiss, 1974)

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).

Acknowledgements

• 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.

Special thanks

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 acidificationKnowing 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.

DICx TA

36 36.2 36.4 36.6 36.8 372380

2390

2400

2410

2420

2430

2440

2450TA=f(S)

Core...

Salinity

TA

2380.0 2385.0 2390.0 2395.0 2400.0 2405.0 2410.0 2415.02030.0

2035.0

2040.0

2045.0

2050.0

2055.0

2060.0

2065.0

2070.0

2075.0

TA

DIC

SSS x TA

The CO2 System

CO2 standards (air with known CO2 concentration:280 ppm, 360 ppm, 500 ppm)

Successive measurements:

• CO2 standards

• Seawater• Atm air• Repeat cycle: standards…

•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 .

Building of a CO2 system in Brazil ongoing at INPE

French system on board the Corenav 3, Oct. 2012

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