Dataset: AN10-12 Surface pCO2 and Chl a
Deployment: AT21-04

Methodology Summary
SST and SSS were continuously monitored using an in-line Seabird thermosalinograph. Chlorophyll a fluorescence (FLR) was recorded by a fluorometer mounted 5-7 m below sea surface, which was then converted to chlorophyll a concentration (Chla) using a linear regression of FLR against discrete Chla measurements of surface water samples collected with Niskin bottles during each cruise. True wind speed was measured shipboard by meteorological instruments on each vessel. Wind speed at 10 m above sea surface (U10) was corrected from instrument heights based on Thomas et al. (2005). Partial pressure of carbon dioxide at sea surface (pCO2_sw) was determined with a showerhead-type pCO2 analyzer (Bates et al., 1998; Sweeney et al., 2000; Takahashi et al., 1997) and an infrared CO2 detector at in-situ SST (Cooley et al., 2007).

pCO2 sampling procedures
The volumetric concentration of CO₂ (xCO₂_(sw), in ppm) was automatically calibrated at least hourly against six CO₂-N₂ gas mixtures containing 0–510 ppm CO₂ (Certified by the National Oceanographic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory, NOAA CMDL, Boulder, Colorado, USA). Sea surface pCO₂ was converted from xCO₂_(sw) and corrected to in-situ SST (see Weiss & Price, 1980, and Takahashi et al., 1993, for details). The gas stream between the equilibrator and the detector was dried, but this filter sometimes failed, leaving gaps in the data along the cruise track where water vapor overwhelmed infrared detection of CO₂. These system failures were apparent and easily removed manually. Instrument accuracy was ±1 µatm and the response (e-folding; Cooley et al., 2007) time was 6, 2, 10 mins for cruises during June 2010, July 2012, and September 2011, respectively.

More details on methodology can be found in Mu et al. (2021).