COLLABORATIVE RESEARCH: Evaluating Calcification on a Hawaiian Coral Reef Using a Novel, Solid-State Total Alkalinity and pH Sensor

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Changing environmental conditions, including ocean warming and ocean acidification, are having a profound impact on the chemistry of the ocean and on marine ecosystems, particularly coral reefs. Net Ecosystem Calcification (NEC) rate is a strong indicator of stress in coral reef systems, but the lack of sensors that can make autonomous measurements at appropriate time and space scales has limited the scientific community's ability to fully examine the factors that drive NEC changes in coral reef environments. This project addresses the sensor limitation by furthering the development of a novel technology that can measure both total alkalinity and pH every 60 seconds. The solid-state sensor design does not rely on chemical reagents that need to be replaced or pollute the environment. The utility of this novel sensor will be proven in Kaneohe Bay Hawaii, one of the most well instrumented and studied coral reef ecosystems in the world. The successful completion of this project will not only improve our understanding of the drivers of NEC variability, but will also provide the community with a new ocean acidification sensor package that could be used to characterize the ocean carbon system under a wide variety of circumstances. The improvements and documentation produced on how to build these sensors will take the community one step closer to having a commercially viable system that could be transitioned to industry. This work will help inform Hawaiian managers as well as those from other Pacific Islands with substantial coral reef structures on how to evaluate the health and growth of their reef systems. This project will also help train the next generation of ocean scientists through support of a postdoctoral associate and graduate student who will learn to apply the sensor to field measurements and ocean carbon research. The solid-state, reagentless sensor package is based on an ISFET coulometric diffusion titration. The investigators propose to build four systems to test key calcification hypotheses that can best be addressed with these new sensors. They will deploy one stationary sensor on a mooring inside Kaneohe Bay Hawaii, in close proximity to an actively growing coral reef, and one stationary sensor on a mooring outside of Kaneohe Bay that is largely representative of the waters entering the reef system. Two additional sensor packages will be mounted in a low profile surface drifter for Lagrangian studies over the reef flat between the moorings. These sensors will provide measurements of seawater carbon chemistry at a resolution and precision not previously possible. The simultaneous characterization of waters entering the reef and leaving the reef will allow the investigators to study the drivers of reef calcification over a wide range of time-scales from minutes to seasons.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.