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

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, A., Brunet, Christian, Schauer, Bernard, Goyet, Catherine and Eischeid, Greg (2000) The international at-sea intercomparison of fCO2 systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean. Marine Chemistry, 72 . pp. 171-192. DOI 10.1016/S0304-4203(00)00080-3.

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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.

Document Type: Article
Keywords: Carbon cycle; Air–sea exchange; Carbon dioxide partial pressure; Intercomparison, RV Meteor, M36/1
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/S0304-4203(00)00080-3
ISSN: 0304-4203
Projects: JGOFS
Date Deposited: 18 Feb 2008 17:24
Last Modified: 22 Aug 2017 07:37

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