pHew

So, last week we were lucky to welcome Kiminori Shitashima from Kyushu University, Japan. Kiminori was presenting his latest progress with an improved pH sensor.
Historically we could only measure pH or pCO2 with any degree of accuracy using large expensive equipment on boats, but with the advent of clever solid-state devices like Kiminori’s we can seriously think about getting high resolution measurements from autonomous platforms.

This is kinda my thing.

Tom trying to pick up a buoy

What’s an autonomous platform?
It’s anything which collects data without a human being there. Most people exclude satellites from that definition though. So we’re talking buoys, weighted frames sat on the sea bed (landers), and various floating and diving vehicles. I’ll talk more about those some other time.

Back to the pH sensors.
pH is a key component to understanding the exchange of pCO2 between the sea and atmosphere and oceanic carbon cycles. Lots of chemical and biological processes in the sea are affected by the pH of the seawater. See the ‘other‘ CO2 problem.

When it comes to making sense of the oceanic pCO2 system there are four parameters; pH, pCO2, alkalinity and total CO2. You can measure and two and calculate the rest. Measuring pH and pCO2 is much much easier than trying to measure the other two.

Traditional glass pH sensors lack the accuracy, response and resolution that’s needed for chemical oceanography. They’re also pretty fragile.
Kiminori’s design is based on a Ion sensitive field effect transistor (ISFET) and solves many of the problems found with the glass sensors.

pH sensor

I won’t go into the details of how it works but suffice to say I’ll be jumping at the first chance to use one myself. It’s very small, low power and robust. All things that lend itself well to using it somewhere difficult like the North Sea on a Wave Glider in February.

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