| Summary: | Maintenance and Update Frequency: asNeeded Statement: The fugacity of carbon dioxide (fCO2) in surface seawater was measured using a General Oceanics Inc. Model 8050 CO2 system (Pierrot et al 2009). Final fugacity data are reported at sea surface temperature and with water saturated air. Seawater from an underway seawater supply is sprayed into an equilibration chamber and CO2 in the headspace gas equilibrates with the seawater. The headspace gas is pumped through a thermoelectric condenser followed by a nafion dryer to remove water vapour before flowing through a Licor 7000 non-dispersive infrared gas analyser used to quantify the CO2 mole fraction (XCO2) of the dried air. The mole fraction measurements are made at atmospheric pressure as gas flow is stopped and the gas line is temporarily vented to the atmosphere. A set of four CO2-in-air standards that cover the range of CO2 values expected in the ocean are analysed about every four hours to calibrate the gas analyser. The standard gas concentrations are on the WMO-X2007 mole fraction scale for CO2-in-air. Atmospheric XCO2 (dry) is measured after the standards by pumping clean outside air from an intake mounted on the forward mast of the ship. The seawater intake is located in the ship bow at about 5.5m below sea level. Sea surface salinity is measured using a thermosalinograph (Seabird Electronics SBE21) located next to the CO2 system and the sea surface temperature is measured using a remote temperature sensor (Seabird Electronics SBE 38) located at the intake is used to measure sea surface temperature (SST). The travel time between the intake and CO2 system is typically about 4 minutes, with warming usually less than 0.6ºC. The thermosalinograph water is from the same intake, but the supply lines separate after the intake and the travel time to the thermosalinograph is about 1.5 minutes. A comparison of thermosalinograph and equilibrator temperature records shows the temperature difference in the two lines is generally less than 0.1ºC. The ...
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