Éditeur(s) :
HAL CCSD Elsevier Résumé : International audience
The ‘International Intercomparison Exercise of
fCO
2 Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (
fCO
2) systems, one discrete
fCO
2 system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater
fCO
2 measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO2, temperature measurements) and a common procedure for calculation of final
fCO
2 were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the
fCO
2 in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete
fCO
2 measurements can be made in good agreement (±3 μatm) with underway
fCO
2 data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the
fCO
2 system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in
fCO
2 results. Calculation of
fCO
2 from high-quality total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements does not yield results comparable in accuracy and precision to
fCO
2 measurements.
ISSN: 0304-4203
hal-01245605
https://hal.archives-ouvertes.fr/hal-01245605 DOI : 10.1016/S0304-4203(00)00080-3