The international at-sea intercomparison of f CO 2 systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean

• Published in: Marine Chemistry
• Main Authors: Körtzinger, Arne, Mintrop, Ludger, Wallace, Douglas W.R, Johnson, Kenneth M, Neill, Craig, Tilbrook, Bronte, Towler, Philip, Inoue, Hisayuki Y, Ishii, Masao, Shaffer, Gary, Torres Saavedra, Rodrigo F, Ohtaki, Eiji, Yamashita, Eiji, Poisson, Alain, Brunet, Christian, Schauer, Bernard, Goyet, Catherine, Eischeid, Greg
• Other Authors: School of Psychological Sciences, University of Melbourne, CSIRO Wealth from Oceans National Research Flagship and Antarctic Climate and Ecosystems CRC, Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI), Laboratoire de Physique et Chimie Marines (LPCM), Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Institut de Modélisation et d'Analyses en géo-environnement et santé - Espace Développement (IMAGES-Espace DEV), UMR 228 Espace-Dev, Espace pour le développement, Université de Guyane (UG)-Université des Antilles (UA)-Institut de Recherche pour le Développement (IRD)-Université de Perpignan Via Domitia (UPVD)-Avignon Université (AU)-Université de La Réunion (UR)-Université de Montpellier (UM)-Université de Guyane (UG)-Université des Antilles (UA)-Institut de Recherche pour le Développement (IRD)-Université de Perpignan Via Domitia (UPVD)-Avignon Université (AU)-Université de La Réunion (UR)-Université de Montpellier (UM)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2000
• Subjects: Intercomparison; Air–sea exchange; Carbon dioxide partial pressure; Carbon cycle; [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph]; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-01245605; https://doi.org/10.1016/S0304-4203(00)00080-3

International audience The ‘International Intercomparison Exercise of f CO 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 ( f CO 2 ) systems, one discrete f CO 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 f CO 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 f CO 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 f CO 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 f CO 2 measurements can be made in good agreement (±3 μatm) with underway f CO 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 f CO 2 system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in f CO 2 results. Calculation of f CO 2 from high-quality total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements does not yield results comparable in accuracy and precision to f CO 2 measurements.