Developing a Reagentless In situ Sensor for Measurements of Dissolved Inorganic Carbon in Seawater

The seawater carbonate system, mainly consisting of dissolved carbon dioxide (CO2), bicarbonate (HCO3-) and carbonate ions (CO3 2-), is an important part of the global carbon cycle. It regulates seawater acidity and the direction and magnitude of CO2 exchange between the ocean and the atmosphere, thus exerting control on ocean acidification (OA) and the changing climate.

Development of sensor technologies to measure the carbonate system parameters efficiently has been widely recognized as a priority in the ocean science community. Dissolved inorganic carbon (DIC), the sum of dissolved CO2, HCO3 - and CO3 2- in seawater, is a master variable that is critical to study a suite of important research questions related to the marine carbon cycle and OA’s impacts on marine biology and ecosystems.

Various prototype in situ DIC sensors have emerged in the past decade. However, these systems require chemical reagents, and are thus complex, have high power requirements, and are limited in deployment duration and observing platforms that can be used. To address these limitations, the goal of this project is to develop a new reagentless in situ DIC sensor for seawater applications using a solid-state sensing technology and reagentless chemical reactions.

The new DIC sensor will have broad applicability to the ocean research community. NOAA Northeast Fisheries Science Center have expressed their interest, if development is successful, to acquire the new DIC sensor to be routinely deployed on their coastal surveys to enhance OA monitoring and improve in situ studies of the effects of OA on ecosystem health and fishery species.

This development may pave the road for much-needed long-term deployments of DIC sensors on gliders and floats that the ocean research community is calling for. One community college student and one local citizen scientist will be recruited for sensor testing through collaboration with Waquoit Bay National Estuarine Research Reserve. Their feedback will help improve the sensor’s operation by non-experts and its overall performance.

This democratized strategy will widen future deployments and applications beyond academia and provide data to stakeholders. This project will support one PhD student through the joint education program between Massachusetts Institute of Technology and Woods Hole Oceanographic Institution (WHOI). It will train one community college student and two undergraduate summer interns through the WHOI Summer Student Fellowship program and the Woods Hole Partnership Educational Program. This project will support diversity, equity, and inclusion through the recruitment of all students.

Developing and ground truthing the first-of-its-kind reagentless in situ DIC sensor constitutes the core of the intellectual merit of this work. The new DIC method will be based on a controlled electro-acidification process to acidify seawater samples followed by optical pCO2 detection. No chemical reagents will be used in this method.

The main objectives of the development include: (1) Develop and optimize the new DIC method in the laboratory to achieve high-quality measurements of DIC in seawater; (2) Adapt the new DIC method into a low-power, prototype sensor system capable of in situ DIC measurements in shallow coastal systems; (3) Test and calibrate the new sensor system in seawater tanks and evaluate its characteristics, performance and long-term stability; (4) Test-deploy the new sensor, along with a suite of other physical and biogeochemical sensors, at a time-series station at Waquoit Bay, MA for extended periods to evaluate the sensor’s in situ performance and stability. The new technology will be a significant technological leap forward, resolving key challenges in current in situ DIC sensing by significantly improving robustness, power consumption, and deployment duration, while reducing cost, complexity, and size.

It thus has the potential to be adapted for many stationary and mobile observing platforms, such as the rapidly growing fleet of surface vehicles, gliders, and biogeochemical floats. This project will significantly improve our capability to study and respond to the marine carbon cycle and ocean acidification.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.