Underway sea surface temperature, salinity, and pCO2 data were collected continuously along the cruise track. Surface seawater was collected from an intake on the port side of the ship at about 4m depth. SST and SSS were measured by an SBE45 (Sea-Bird Electronics) Thermosalino graph installed in the sea chest. Seawater was pumped to the ship's labs. There, underway pCO2 was measured inline by an automated system (Apollo Scitech) with a Li-7000 (LICOR, Inc.) non-dispersive infrared detector at a water flow rate of 3-4L/min; The sampling interval was 2 min. This autonomous system was twice daily against three certified CO2 gas standards (150.62, 404.72, and 992.54 ppm) obtained from NOAA's Earth System Research Laboratory (ESRL), Global Monitoring Division in Boulder, CO. These gas standards are directly traceable to the World Meteorological Organization (WMO) scale. The precision of underway pCO2 measurements of this system is 0.1 μatm, and the overall accuracy is estimated at 2 μatm, as documented by Pierrot et al. (2009). The underway system uses a shower head type equilibrator with ~0.5L headspace volume.
Instruments:
Underway pCO2 was measured inline by an automated system (Apollo Scitech) with a Li-7000 (LICOR, Inc.) non-dispersive infrared detector .
The pCO2 measurement was calibrated twice daily against 3 certified CO2 gas
standards (150.62, 404.72, and 992.54 ppm)
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