Dataset: Moorings - Temp Sal O2 pH
Deployment: SeapHOx_Kelp_A

To calibrate the pH sensors, discrete water samples were taken during each SeapHOx deployment for the determination of total alkalinity (TA) and total dissolved inorganic carbon (DIC). The calibration samples were collected via SCUBA next to the sensor with a 5L niskin bottle. The collected seawater was transferred to a 500 ml clean borosilicate glass bottle with a ground glass neck and stopper. The samples were poisoned with a saturated mercuric chloride solution. TA measurements were determined using an open-cell, potentiometric titration (Dickson et al. 2007).  DIC measurements were determined by acid extraction and coulometric detection of CO2 (Dickson et al. 2007). pH was calculated from TA and DIC using the Matlab version of CO2SYS (van Heuven et al. 2011) as recommended by Dickson et al. 2007. The calculated pH at in situ temperature from the calibration sample was used to determine the electrode-specific calibration coefficients. The calibration sample produced a pH accuracy of 0.01 units for each SeapHOx instrument. The oxygen sensors were factory calibrated by Aanderaa and before each deployment a two-point (0% and 100% saturation) offset was applied as recommended in the manual.

References:

Martz, T. R., Connery, J. G., and Johnson, K. S.: Testing the Honeywell Durafet® for seawater pH applications, Limnol. Oceanogr. Methods, 8, 172-184, 2010.

Dickson, A. G., Sabine, C. L., and Christian, J. R.: Guide to Best Practices for Ocean CO2 5 Measurements, Vol. 3, 374 PICES Spec. Publ., Sidney, British Columbia, 2007.

van Heuven et al. 2011. Matlab version of CO2SYS.