USGS Cooperative Ecosystem Studies Unit, Gulf Coast CESU Grant: Development of pH Measuring Device

A large fraction of the CO2 released to the atmosphere each year (approximately one quarter) enters the ocean. This oceanic uptake of CO2 has profound consequences for the global ocean. In a process widely known as `ocean acidification¿, nearly every CO2 molecule entering the surface ocean from the atmosphere produces a hydrogen ion. This acidification process reduces pH, reduces calcium carbonate saturation states, alters the speciation of many chemicals, and has been shown to have myriad biological effects. A particularly important problem associated with ocean acidification is that, while it is widely acknowledged that observations of pH are essential context for a wide range of modern-day biogeochemical investigations, facile measurement of seawater pH on broad spatial scales and finely resolved temporal scales has proven to be problematic. Furthermore, measurements of pH in salinity ranges from freshwater to seawater, as is typical in estuaries and coastal areas, has been hampered by lack of inexpensive, versatile instrumentation and calibration issues. Spectrophotometric devices capable of measuring pH with high accuracy are typically expensive, Ion Selective Field Effect Transistor devices (ISFETs) are expensive and require frequent calibration, and glass electrodes, although relatively inexpensive, require frequent calibration and are frequently unreliable.