Reliably Measuring pH in the Ocean

Although it’s barely the size of a breath mint, the Ag/AgCl reference allows the Deep SeapHOx V2 to dive deeper than any other pH sensor. Learn how a solid-state reference electrode allows the SeaFET V2, SeapHOx V2, and Deep SeapHOx V2 retain accuracy across a much broader range of temperature and pressure than standard pH sensors.

The liquid-filled electrode used by most pH sensors is a tried and tested method of obtaining in-situ pH data. However this design has noteworthy limitations for use in the ocean: the electrochemical properties of these electrodes make them notoriously unstable in seawater, and a liquid reference generally requires a junction that is intolerant of high pressures, keeping it out of the deeper reaches of the ocean.

Enter the solid-state Ag/AgCl reference electrode: originally (and still included) on the Shallow SeaFET, it has been refined for use on the 2000m capable Deep SeapHOx. Along with the ISFET pH sensor and a pressure-tolerant housing, the little Ag/AgCl puck is helping open the door for high-quality pH measurements across a broader range of temperature and pressure than ever before.

Sea-Bird Scientific vetted this technology in 2015 in the Wendy Schmidt Xprize competition, and continued to refine the calibration process for accuracy across a greater depth and temperature range. Today, this technology is present on the SeaFET V2, SeapHOx V2, Deep SeapHOx V2, and Float pH sensors.

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