Dataset: CO2 parameters as function of salinity and temperature

CO2 system parameters were collected over salinity 20 to 40 and temperature 5 to 40 degree range. Seawater was collected from offshore in Golf of Mexico. Salinity other than 35 were obtained by either evaporation or dilution. 1 liter sample was put in constant waterbath, CO2 gases from 200 ppm to 2000 ppm(200, 400, 600, 800, 1000, 1300, 1600 and 2000 ppm) were used to bubble the sample at rate of 100 ml/min until the solution reached equilibration with each gas. pH, DIC and TA samples were taken from each sample bottle for analysis.

Sampling and Analytical Procedures

The dataset is a laboratory collection of CO2 parameters under a controlled environment. The experiment involved equilibrating CO2 gases with samples at different salinities and temperatures.
pH was measured using purified mCP ((Liu et al. 2011)) on Agilent 8453 following the protocol of SOP 6b (Dickson et 2017). For low-temperature data, a measurement system was built in the waterbath to ensure the temperature of pH measurement was the same as the sample. Samples were drawn using PEEK tubing by gravity into dried 10 cm cylindrical cells. 3 cell volume was allowed to overflow to ensure uncontaminated sample. Collected sample were thermostatted at equilibrating temperature and analyzed. Two indicators additions were made to get an assessment of indicator perturbation for each sample.

DIC was measured using a custom-built acidification module (Liu et al. 2018). The instrument was built directly in the equilibration waterbath to ensure samples were in equilibration at the proper temperature. The instrument was equipped with a two position Vici switch to automate the sample introduction and acidification process, and a multiposition Vici switch to sample up to 10 samples automatically. The evolved CO2 was measured either by coulometry by UIC or Picarro’s CRD instrument. DIC was calibrated with CRM provided by Andrew Dickson’s lab.

After pH and DIC samples were drawn, TA samples were taken. The sample was weighed on a balance. TA was measured using a custom built single point titration system (Liu et al. 2015 ).
xCO2 of the equilibrating gases were measured on Picarro CRD instruments using two standard gases traceable to NIST.