A multi-sensor system for the direct measurement of Ω, pH, and carbonate

Chair: Libby Jewett

Christina M. McGraw (1), Wayne D.N. Dillon (1), Hugh L. Doyle (2), Peter W. Dillingham (1), Peter G. Lye (1), Philip W. Boyd (2), Catriona L. Hurd (2)

1 School of Science and Technology, University of New England, Armidale, 2351, New South Wales, Australia
2 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, 7005, Tasmania, Australia

Background
A multi-sensor system was developed to monitor short-term carbonate variability in the laboratory and field. The system combines a saturation state (Ω) sensor with carbonate and pH sensors to measure real-time changes in carbonate chemistry.

Methods
The Ω probe detects real-time dissolution and precipitation of calcium carbonate. For example, thin films of CaCO3 with known morphology and thickness can be deposited on the Ω sensor through chemically-controlled deposition. With a sub-second response time, the sensor can then be used to study real-time dissolution under a range of environmental conditions. To complement these measurements, the Ω sensor was combined with a range of seawater sensors we previously developed for ocean acidification studies. To measure carbonate, solid-contact fabrication techniques were used to produce carbonate ion-selective electrodes. The same fabrication techniques were used to produce hydrogen ion-selective electrodes and reference electrodes. The carbonate, hydrogen, and reference electrodes were produced on a single $5 disposable cartridge.

Findings
The ion-selective electrode cartridge and Ω sensor were incorporated into a single multi-sensor array. This device was tested in solutions of known DIC and AT and under a range of current and future conditions. The response of the multi-sensor array varied as expected to the range of solutions and both short-term and long-term variability.

Conclusions
To our knowledge, the multi-sensor array is the first sensor that directly measures Ω, pH, and carbonate. When deployed in the laboratory or field, the device can be used for real-time identification of under-saturation events.