The autonomous measurement of dissolved carbon dioxide (CO2) is of great and still increasing importance for addressing many scientific as well as socio-economic questions.

Although there is a need for reliable, fast and easy-to-use instrumentation to measure the partial pressure of dissolved CO2 (pCO2) in situ, only few autonomous underwater sensors are available.Here we present the measuring principle as well as the latest development state of a commercial sensor (HydroC™/CO2, CONTROS Systems & Solutions GmbH, Kiel, Germany), which is optimized in a collaboration between the IFM-GEOMAR and the manufacturer.

In situ tests and laboratory experiments are essential parts of the comprehensive optimization process, which aims at the successful autonomous long-term deployment on e.g. surface buoys, underwater observatories and floats.