At-sea intercomparison of two newly designed underway pCO(2) systems - Encouraging results

Two newly designed underway systems for the measurement of CO2 partial pressure (pCO(2)) in seawater and the atmosphere are described. Results of an intercomparison experiment carried out in the North Sea are presented. A remarkable agreement between the two simultaneously measured pCO(2) data sets was observed even though the spatial variability in surface pCO(2) was high. The average difference of all 1-min averages of the seawater pCO(2) was as low as 0.15 mu atm with a standard deviation of 1.2 mu atm indicating that no systematic difference is present. A closer examination of the profiles shows that differences tend to be highest during maxima of the pCO(2) gradient (up to 14 mu atm/min). The time constants of both systems were estimated from laboratory experiments to 45 s, respectively, 75 s thus quantitatively underlining their capability of a fast response to pCO(2) changes.