A new automated underway system for making high precision pCO(2) measurements onboard research ships

We have developed a new temperature-controlled, automated underway system f or making atmospheric and surface ocean pCO(2) measurements onboard researc h ships equipped with an uncontaminated seawater intake system. Uncontamina ted seawater is supplied to a showerhead plexiglass equilibrator. After abo ut 3 min, the air trapped in the equilibrator is equilibrated with seawater . This air is sampled six times per hour. In addition, atmospheric air is s ampled three times per hour TM tubing to the underway system. from the inta ke on the bow flagstaff through 3/8 in. Dekabon(TM) tubing to the underway system. The CO2 measurements are made with a differential, non-dispersive, infrared analyzer Li-Cor(TM) (model 6252). The underway system operates on an hourl y cycle with the first quarter of each hour devoted to calibration with thr ee CO2 standards, each measured for 5 min. A second-order polynomial calibr ation curve is calculated from the voltage values of the standards. The rem aining time in each hour is used to measure equilibrator air (15 min), bow air (15 min), and equilibrator air once again (15 min). To date, we have su ccessfully used the underway pCO(2) system on 12 cruises of the NOAA Ship K a'imimoana in the Equatorial Pacific. The analytical precision of the syste m is approximately 0.3-0.4 ppm CO2 for seawater and for air. (C) 1998 Elsev ier Science B.V. All rights reserved.