Measurements of Surface Seawater fCO2 from Volunteer Commercial Ships: Techniques and Experiences from Skaugran

Abstract

Chemical measurements made in the northern North Pacific from a commercial volunteer observing ship (VOS) program during March 1995?March 1998 are presented. Quasi-continuous measurements of the fugacity of CO2 (fCO2, which takes into account the nonideal nature of the gas; the values are within 0.5?1.5 ?atm of the partial pressure in surface water) in seawater were made from two independent systems with different designs, and those results are emphasized here. One system used a fast response bubbling equilibrator with measurements each minute; the other system used a showerhead equilibrator with hourly measurements. Comparison of the results from these side-by-side systems provides useful information about the requirements for making high quality measurements of surface seawater and atmospheric fCO2. From this comparison, the fast response system is deemed to be more stable and potentially more accurate. The utility of this system in waters with high spatial variability is also demonstrated. Factors contributing to the success of this ship-of-opportunity program are discussed as a guidepost for future observing programs.