pCO₂

Analytical Method

In October 1996 (HOT-76) an automated, semi-continuous system for measuring the partial pressure of carbon dioxide in seawater was installed in-line with the ship's clean-seawater intake system to measure underway surface seawater PCO₂. The system is calibrated using three standard gases of known CO₂ concentrations covering the range of 200-400 ppm (Scott Specialty Gases calibrated at SIO). A separate reference gas calibrated at 349.0 ppm is measured for quality assurance. Calibration and standardization are done at system startup and approximately every 2.5 hours. The present system consists of a shower head equilibrator operating at a flow rate of approximately 81 min^-1. Equilibrated gas and bow air are both sampled every 10 minutes. The gases pass through a napthyon tube drier and a magnesium Perchlorate scrubber into a LICOR 6250 infrared detector. The reference chamber is purged with reference gas after every 3 cycles of bow/equilibrator measurements. Gas flow rates into the detector are at approximately 0.51 min^-1. The system output gives the CO₂ concentration of the bow-intake air and the surface seawater in ppm. The system begins operating when the ships is in clean open water and is fully operational at Station Kahe. The system is turned off after departing the last station.

Data are unavailable at present.