The international at-sea intercomparison of fCO₂ systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean

Arne Körtzinger , Ludger Mintrop , Douglas W.R Wallace , Kenneth M Johnson (1) , Craig Neill , Bronte Tilbrook (2) , Philip Towler , Hisayuki y Inoue , Masao Ishii (3) , Gary Shaffer , Rodrigo F Torres Saavedra , Eiji Ohtaki , Eiji Yamashita , Alain Poisson (4) , Christian Brunet (4) , Bernard Schauer (4) , Catherine Goyet (5) , Greg Eischeid

1 School of Psychological Sciences
2 CSIRO Wealth from Oceans National Research Flagship and Antarctic Climate and Ecosystems CRC
3 AWI - Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung = Alfred Wegener Institute for Polar and Marine Research = Institut Alfred-Wegener pour la recherche polaire et marine
4 LPCM - Laboratoire de Physique et Chimie Marines
5 IMAGES-Espace DEV - Institut de Modélisation et d'Analyses en géo-environnement et santé - Espace Développement

The ‘International Intercomparison Exercise of fCO₂ 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 (fCO₂) systems, one discrete fCO₂ 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 fCO₂ 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 fCO₂ were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO₂ 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 fCO₂ measurements can be made in good agreement (±3 μatm) with underway fCO₂ 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 fCO₂ system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO₂ results. Calculation of fCO₂ from high-quality total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements does not yield results comparable in accuracy and precision to fCO₂ measurements.

Mots clés: Intercomparison; Air–sea exchange; Carbon dioxide partial pressure; Carbon cycle

Domaines: Géophysique [physics.geo-ph]

Arne Körtzinger, Ludger Mintrop, Douglas W.R Wallace, Kenneth M Johnson, Craig Neill, et al.. The international at-sea intercomparison of fCO₂ systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean. Marine Chemistry, 2000, 72 (2-4), pp.171-192. ⟨10.1016/S0304-4203(00)00080-3⟩. ⟨hal-01245605⟩