Collaborative Research: Accelerated Development of New, Scalable pH Sensors for Global Ocean Observational Networks

The DuraFET pH sensor is a key component of global observation networks through coordinated efforts such as Biogeochemical Argo and the Global Ocean Acidification Observation Network. These pH sensors have been deployed on hundreds of autonomous profiling floats, underwater gliders, and moorings to study ocean carbon cycling in environments ranging from the intertidal zone, coral reefs, to the open ocean. Additionally, they are commonly utilized in laboratory mesocosms to study impacts of ocean acidification. The key enabling technology for the DuraFET is an Ion Sensitive Field Effect Transistor (ISFET) semiconductor chip, manufactured by Honeywell Co. The Honeywell ISFET has several unique features that give it superior performance relative to its competitors. This in essence results in a sole-source for DuraFET pH sensors, and represents a key vulnerability for ocean carbon monitoring. To address this, this proposal aims to accelerate the development of alternative pH sensors that can be scaled to fit the current needs of global ocean observational networks. Specifically, this project will test and develop two promising pH sensor candidates that are capable of long-term deployments (years) to 2 km depth on autonomous platforms such as profiling floats and gliders, as well as for moored instrumentation and laboratory mesocosm applications. First, the performance of a commercially available optical pH optode sensor (distributed by PyroScience) will be assessed. This is a relatively new sensor for oceanography, thus its performance has not been thoroughly characterized to the satisfaction of chemical oceanographers. Second, a pH sensor that utilizes an ISFET from a different supplier will be developed. Both pH sensors that will be explored are solid state, small, and low-power, making them good candidates for autonomous platforms. The sensors will be thoroughly characterized in the laboratory for pH response, long term drift, salinity, temperature, and pressure effects, response time, and hysteresis. Both sensors will then be deployed on coastal moorings, underwater gliders, and profiling floats to assess in situ performance across a range of conditions over months to years. Results from this development will be rapidly and efficiently shared with the oceanographic community through recurring webinars, publications, and collaboration with industry. 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.