title: Deep-Sea DuraFET: A Pressure Tolerant pH Sensor Designed for Global Sensor Networks.
abstract: Increasing atmospheric carbon dioxide is driving a long-term decrease in ocean pH which is superimposed on daily to seasonal variability. These changes impact ecosystem processes, and they serve as a record of ecosystem metabolism. However, the temporal variability in pH is observed at only a few locations in the ocean because a ship is required to support pH observations of sufficient precision and accuracy. This paper describes a pressure tolerant Ion Sensitive Field Effect Transistor pH sensor that is based on the Honeywell Durafet ISFET die. When combined with a AgCl pseudoreference sensor that is immersed directly in seawater, the system is capable of operating for years at a time on platforms that cycle from depths of several km to the surface. The paper also describes the calibration scheme developed to allow calibrated pH measurements to be derived from the activity of HCl reported by the sensor system over the range of ocean pressure and temperature. Deployments on vertical profiling platforms enable self-calibration in deep waters where pH values are stable. Measurements with the sensor indicate that it is capable of reporting pH with an accuracy of 0.01 or better on the total proton scale and a precision over multiyear periods of 0.005. This system enables a global ocean observing system for ocean pH.
authors.affiliation: Monterey Bay Aquarium Research Institute , 7700 Sandholdt Road, Moss Landing, California 95039, United States.
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Johnson
authors.affiliation: Monterey Bay Aquarium Research Institute , 7700 Sandholdt Road, Moss Landing, California 95039, United States.
authors.forename: Hans W
authors.initials: HW
authors.lastname: Jannasch
authors.affiliation: Monterey Bay Aquarium Research Institute , 7700 Sandholdt Road, Moss Landing, California 95039, United States.
authors.forename: Luke J
authors.initials: LJ
authors.lastname: Coletti
authors.affiliation: Monterey Bay Aquarium Research Institute , 7700 Sandholdt Road, Moss Landing, California 95039, United States.
authors.forename: Virginia A
authors.initials: VA
authors.lastname: Elrod
authors.affiliation: Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, California 92093, United States.
authors.forename: Todd R
authors.initials: TR
authors.lastname: Martz
authors.affiliation: Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, California 92093, United States.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Takeshita
authors.affiliation: Honeywell Aerospace, 12001 Highway 55, Plymouth, Minnesota 55441, United States.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Carlson
authors.affiliation: 215 E. Welsh Road, Maple Glen, Pennsylvania 19002, United States.
authors.forename: James G
authors.initials: JG
authors.lastname: Connery