37th International Liège Colloquium on Ocean Dynamics, GAS TRANSFER AT WATER SURFACES, May 2- 6 2005 Temporal variability of atmospheric CO2 in the Bay of Biscay

• Main Authors: Padin X. A, F. F. Perez, A. Rios
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Liège; Mace; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.521.9878; http://modb.oce.ulg.ac.be/backup/colloquium/padin.pdf

The objective of the project “ECO ” is to investigate the anthropogenic CO2 uptake capability off the Galician coast and Bay of Biscay on a seasonal time scale. Subpolar Eastern North Atlantic waters are formed in the Bay of Biscay and consequently the area plays an important role in the carbon flux to the ocean interior [Follows et al., 1996]. To carry out this project, an unattended pCO2 measuring system, coined “GASPAR ” has been installed on board of the RO-RO L’Audace, that usually covers the route Vigo (Spain)- St. Nazaire (France) with a frequency of 12 times per month. Continuous measurements of pCO2 in air and seawater, temperature, salinity, oxygen, fluorescence and speed and direction of wind were recorded during 2003-2004. The atmospheric pCO2 measurements carried out on board can be easily contaminated by the own vesel emisions because of that pCO2 atmospheric measurements from fixed meteorological stations are usually considered to estimate the ocean atmosphere fluxes. We have filtered the atmospheric pCO2 taking into account the local wind, removing the data under the influence of the vessel emissions and applying also the quality control of atmospheric samples followed Komhyr (1985). We have estimated the seasonal cycle for the filtered molar fraction of CO2 in the inner part of Bay of Biscay and we have obtained an annual amplitude of 11 umol/mol and an annual increasing of 2 umol/mol. The temporal evolution of the filtered molar fraction of CO2 in the inner part of the Bay of Biscay shows a similar trend to the time serie data of two fixes meteorological stations, one in Azores (Portugal) and the other in Mace Head (Irland). Using this approach for atmospheric pCO2 we avoid the under/overestimate of air-sea CO2 fluxes that can represent even a 50 % of error over short time periods. For longer time scales, the use of atmospheric pCO2 seasonal mean value from fixed stations has no significant effect on the final net magnitude of the air–sea flux, with a difference around 1 % for the entire year.