Abstract

Autonomous underwater gliders offer the capability of measuring oceanic parameters continuously at high resolution, on timescales that can extend to many months. An experimental ion-sensitive field-effect transistor (ISFET) sensor measuring pH was attached to a glider during the REP14 -MED experiment in June 2014 in the Sardinian Sea. Water samples were collected from a nearby ship and analysed for DIC and AT to derive pH for validating the ISFET sensor measurements. The vertical resolution of the pH sensor was good (1 to 2 m), but stability was poor and the sensor drifted in a non-monotonous fashion. Corrections were applied to sensor measurements to account for drift, and temperature and pressure effects. Furthermore, Sunlight caused an apparent sensor pH decrease of up to 0.1 in surface waters around local noon, highlighting the importance of shielding the sensor from light in future deployments. The corrected pH from the ISFET sensor is presented along with other parameters measured by the glider, providing insights into the physical and biogeochemical variability in the Sardinian Sea.