CO2 MEASUREMENTS ON THE PIRATA NETWORK

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CO2 MEASUREMENTS ON THE PIRATA NETWORK
Nathalie Lefèvre, IRD LOCEAN Nathalie.lefevre
_at_locean-ipsl.upmc.fr
Presented by Fabrice Hernandez, IRD/Mercator Ocean
PIRATA 12 meeting, Miami, 1-3 November 2006
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Scientific objectives
European project CARBOOCEAN (theme 1, WP4)
Estimate the flux of CO2 at the air-sea interface
by developing an observational network for CO2
Network for the tropical Atlantic
? 2 merchant ships (France-Brazil, red line,
France-French Guiana, green line) equipped with
an automated CO2 system to measure atmospheric
and oceanic CO2 underway by infrared detection.
? 2 CO2 sensors for PIRATA moorings at 6oS, 10oW
and 8oN, 38oW (black dots) using a colorimetric
method (CARIOCA buoy technology).
EGEE 3 cruise (in blue)
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Choice of the PIRATA moorings for installing CO2
sensors
CO2 sensors on PIRATA moorings
6oS, 10oW CO2 time-series in the SEC
8oN, 38oW CO2 time-series in the NECC
SeaWiFs, Septembre 2003
Impact of the Amazon outflow on the CO2
distribution during the retroflection of the
North Brazil Current (NBC) Advection far East i
n the North Equatorial Counter-Current (NECC)
10W
40W
10S
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Installation of the first CO2 sensor on the
PIRATA mooring at 6oS, 10oW during the EGEE 3
cruise (June 2006)
Argos antenna
CO2 sensor and oxygen optode
Box with electronics
CO2 sensors built at DT INSU (Antoine Guillot,
Théo Danguy, Laurence Beaumont)
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Data of the CO2 sensor since the 7th of June 2006
Hourly measurements of CO2, SST and O2 sent by
ARGOS
367 micro-atm
SST decrease due to the upwelling (June-September)
CO2 increase
pCO2 -19.54 SST 895.84 r2 -0.88
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Correlation between pCO2 and SST and SSS
Detrended and normalized hourly pCO2, sea surface
temperature and sea surface salinity
(interpolated from PIRATA daily records) as a
function of time (in days). Data from 8 June to 7
October 2006.
Colder and fresher seawater associated with
higher CO2 concentrations
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Diurnal cycle consistent with biological activity

• Dissolved inorganic carbon (DIC) calculated (does
  not depend on temperature)
  
• Decrease of DIC during the day
• (photosynthesis)
• Increase of DIC during the night
• (convection respiration)

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Air-sea CO2 flux
Calculation of the flux using the formula
F k.S.(pCO2 ocean pCO2 atm) - k is a gas
exchange coefficient depending on the wind speed
(PIRATA wind speed converted to a 10m wind
speed), it is calculated using the formula of
Wanninkhof (1992) - S is the solubility of CO2 (W
eiss et al., 1974) - pCO2 atm is the atmospheric
pCO2 measured during EGEE 3 (367 matm)
Source of CO2 4.56 m.mol.m-2.d-1 (8 June 7
October 2006) ranging from 1.19 in June to 6.82
m.mol.m-2.d-1 in September
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Conclusions perspectives

• Time-series set up at the PIRATA mooring at 6oS,
  10oW to monitor the CO2 variability in the
  eastern part of the tropical Atlantic (in the
  South Equatorial Current).
• Replace the sensor (lifetime of 1 year) during
  EGEE 5 (June 2007) to continue the time-series
  (the existing one is sent for calibration,
  renewal of the dye at the DT INSU while a spare
  one is installed).
• ? Funding obtained to install a CO2 sensor at
  8oN, 38oW during the PIRATA Brazil cruise in 2007
  (NECC and monitoring of the Amazon discharge in
  the tropical Atlantic).