Ž . Marine Chemistry 72 2000 171–192 www.elsevier.nlrlocatermarchem The international at-sea intercomparison of f CO systems during 2 the RrV Meteor Cruise 36r1 in the North Atlantic Ocean Arne Kortzinger a, ) , Ludger Mintrop a,b , Douglas W.R. Wallace a , ¨ Kenneth M. Johnson a,c , Craig Neill c , Bronte Tilbrook d , Philip Towler d , Hisayuki Y. Inoue e , Masao Ishii e , Gary Shaffer f , Rodrigo F. Torres Saavedra g , Eiji Ohtaki h , Eiji Yamashita i , Alain Poisson j , Christian Brunet j , Bernard Schauer j , Catherine Goyet k , Greg Eischeid k a Department of Marine Chemistry, Institute of Marine Research at the UniÕersity of Kiel, Dusternbrooker Weg 20, 24105 Kiel, Germany ¨ b Department of Geosciences, UniÕersity of Bremen, PO Box 330440, 28334 Bremen, Germany c Department of Applied Science, BrookhaÕen National Laboratory, PO Box 5000, Upton, NY 11973-5000, USA d DiÕision of Marine Research, Co-operatiÕe Research Centre for Antarctic and Southern Ocean, and Commonwealth Scientific and Industrial Research Organisation, PO Box 1538, Hobart, TAS 7001, Australia e Geochemical Research Department, Meteorological Research Institute, Nagamine 1-1, Tsukuba, Ibaraki 305, Japan f Danish Center for Earth System Science, UniÕersity of Copenhagen, Juliane Maries Õej 30, 2100 Copenhagen, Denmark g Department of Analytical and Marine Chemistry, Goteborg UniÕersity, 412 96 Goteborg, Sweden ¨ ¨ h EnÕironmental Science and Technology, Okayama UniÕersity, Tsushima-Naka 2-1-1, Okayama 700, Japan i Research Institute of Technology, Okayama UniÕersity of Science, Ridai-cho 1-1, Okayama 700, Japan j Laboratoire de Physique et Chimie Marines, UniÕersite Pierre et Marie Curie, Case 134, 75252 Paris Cedex 05, France ´ k Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA Received 29 July 1999; received in revised form 23 December 1999; accepted 7 August 2000 Abstract The ‘International Intercomparison Exercise of f CO Systems’ was carried out in 1996 during the RrV Meteor Cruise 2 Ž 36r1 from BermudarUK to Gran CanariarSpain. 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 Ž . f CO systems, one discrete f CO system, and two underway p H systems, as well as systems for discrete measurement of 2 2 total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater f CO measured synchronously by 2 Ž . all participating instruments. A common infrastructure seawater and calibration gas supply , different quality checks Ž . performance of calibration procedures for CO , temperature measurements and a common procedure for calculation of 2 final f CO were provided to reduce the largest possible amount of controllable sources of error. The results show that under 2 such conditions underway measurements of the f CO in surface seawater and overlying air can be made to a high degree of 2 Ž . agreement "1 matm with a variety of possible equilibrator and system designs. Also, discrete f CO measurements can be 2 ) Corresponding author. Ž . E-mail address: akoertzinger@ifm.uni-kiel.de A. Kortzinger . ¨ 0304-4203r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0304-4203 00 00080-3