Recommendations for autonomous underway pCO2 measuring systems and data-reduction routines

In order to facilitate the collection of high quality and uniform surface water pCO(2) data, an underway pCO(2) instrument has been designed based on community input and is now commercially available. Along with instrumentation, agreements were reached on data reduction and quality control that can be easily applied to data from these systems by using custom-made freeware. This new automated underway pCO(2) measuring system is designed to be accurate to within 0.1 mu atm for atmospheric pCO(2) measurements and to within 2 mu atm for seawater pCO(2), targeted by the scientific community to constrain the regional air-sea CO2 fluxes to 0.2 Pg C year(-1). The procedure to properly reduce the underway pCO(2) data and perform the steps necessary for calculation of the fugacity Of CO2 from the measurements is described. This system is now widely used by the scientific community on many different types of ships. Combined with the recommended data-reduction procedures, it will facilitate producing data sets that will significantly decrease the uncertainty currently present in estimates of air-sea CO2 fluxes. (C) 2008 Elsevier Ltd. All rights reserved.