The TRICUSO team at partner GEOMAR has recently achieved a project milestone of advancing data quality improvement of the SubCtech OceanPack™ through a dedicated long-term laboratory trial.
As the standard pCO2 system fitted on racing yachts, the SubCtech membrane instrument represents both a proven platform and a significant opportunity for the ocean observing community. Forming part of TRICUSO’s objectives within Work Package 2, this milestone focuses on improving the quality of data returned by membrane-based systems through a long-term laboratory deployment at GEOMAR under simulated in situ conditions, using a dedicated pCO2 validation unit. In close collaboration with fellow TRICUSO partner SubCtech, the GEOMAR team is working to systematically identify and resolve remaining weaknesses in the membrane-based measurement approach, with the aim of delivering demonstrably improved data quality by the end of the project. An upcoming workshop with the racing yacht industry will additionally define specifications for next-generation instruments, driving continual innovation throughout the project.
Why is This an Important Milestone?
The ocean absorbs approximately one third of anthropogenic CO2 emissions annually, making continuous, high-quality surface ocean carbon measurements critical for constraining air–sea flux estimates and understanding long-term changes in the ocean carbon sink. Compact underway systems such as the OceanPack™ are well positioned to fill observational gaps when installed on vessels of opportunity (racing yachts, tourist and industry ships). However, their scientific utility depends directly on the reliability of the data they deliver — making systematic characterisation and reduction of measurement uncertainties a prerequisite for operational deployment.
How Does the OceanPack™ Actually Work?
Seawater is continuously pumped from the ship’s hull through the instrument, where it flows along a thin semipermeable membrane. CO2 diffuses across the membrane and equilibrates with a small enclosed air volume, which is subsequently analysed by a high-sensitivity infrared sensor to yield a precise pCO2 reading. The instrument additionally records water temperature, salinity, and pressure, with optional dissolved oxygen measurements, providing a versatile and compact package for surface ocean monitoring.
Putting it to the Test – In the Lab and at Sea
To systematically identify sources of measurement error, the GEOMAR team established a long-term laboratory deployment in which an OceanPack™ unit was connected to a reference seawater tank equipped with certified reference gases and an independent CO2 sensor. This validation setup enables direct comparison between instrument output and known reference values, allowing deviations to be detected and attributed.
Initial dry tests examined instrument response to controlled temperature variations, followed by wet runs with active seawater circulation. Among the questions under investigation is the minimum reference gas consumption required to maintain accuracy — a parameter of direct operational relevance for long deployments far from resupply.
A short dockside trial conducted aboard Boris Herrmann’s racing yacht Seaexplorer while moored in Kiel ahead of the Ocean Race Europe 2025 provided an opportunity to compare OceanPack™ temperature readings against a high-precision reference sensor. A systematic offset of 0.1 °C was identified — sufficient to introduce an uncertainty of approximately 1.6 µatm in the derived pCO2 value. The 30-minute duration of the trial limits definitive conclusions, and longer deployments spanning a wider range of temperature conditions will be required to fully characterise this bias.
Seven Weeks in the Labrador Sea
The most extensive evaluation to date was conducted during research cruise MSM142 in the Labrador Sea, where the OceanPack™ operated continuously aboard the German research vessel Maria S. Merian for seven weeks under real ocean conditions. The resulting dataset is currently being processed and is expected to directly inform the next iteration of instrument improvements — whether through additional internal temperature sensors, enhanced carrier gas drying, or refined calibration procedures.
Why Does This Matter?
Beyond racing yachts, compact underway systems like the OceanPack™ have the potential to be deployed on ferries, cargo ships, and other vessels of opportunity already crossing remote ocean regions that research vessels rarely reach. Realising this potential, however, depends entirely on the reliability of the data they deliver — making the systematic improvement of measurement quality not just a technical objective, but a prerequisite for meaningful contribution to the global ocean observing system.
Milestone story written by Kristin Kampen and Tobias Steinhoff, GEOMAR.
