Performance of the Deep-Sea-Durafet pH sensor on a Spray Glider in the Central California Current System

The California Current System is thought to be particularly vulnerable to ocean acidification, yet pH remains chronically undersampled along this coast, limiting our ability to make accurate projections of pH conditions and to assess the current and future impacts of ocean acidification. In order to address this technological need, we have integrated the Deep-Sea-Durafet, a solid state pH sensor onto a Spray underwater glider; this pH sensor is identical to those deployed on profiling floats. Here, we present results from 5 deployments over 8 months with a total of over 100 glider days and > 1,000 dives to depths of up to 1,000 m along the Central California coast. Similar to profiling floats, the pH sensor was calibrated for temperature and pressure effects prior to deployment, and an offset was applied based on a deep pH reference field derived from empirical algorithms. Reliable calibration could be obtained using global algorithms as close as 25 km from shore and 500 m depth. Using this correction, the glider pH data agreed to discrete samples to better than ± 0.01 (RMSE, n = 72). No noticeable drift in the calibration coefficients were observed between deployments. These results are an enabling step towards routine pH glider operations along the California Current System.