AT-SEA INTERCOMPARISON OF 2 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. Resul ts of an intercomparison experiment carried out in the North Sea are p resented. A remarkable agreement between the two simultaneously measur ed pCO(2) data sets was observed even though the spatial variability i n surface pCO(2) was high. The average difference of all 1-min average s of the seawater pCO(2) was as low as 0.15 mu atm with a standard dev iation of 1.2 mu atm indicating that no systematic difference is prese nt. A closer examination of the profiles shows that differences tend t o 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 e xperiments to 45 s, respectively, 75 s thus quantitatively underlining their capability of a fast response to pCO(2) changes.