Project: Development of a Compact Instrument for Field Measurements of pH, Total Dissolved Inorganic Carbon and Total Alkalinity

Extracted from the NSF award abstract:

Ocean acidification, most generally described as resulting from the uptake of atmospheric carbon dioxide by surface ocean waters, has importance consequences for ocean chemistry and for marine organisms. Understanding these changes and their consequences requires an understanding of the complex chemistry of the dissolved carbon dioxide (or carbonate) system in seawater, and the ability to accurately and precisely measure small changes in carbonate system parameters. Such measurements require specialized training and are beyond the specific expertise of many investigators who would like to pursue research related to ocean acidification. This project will support the development of a portable, automated instrument that will enable investigators with limited backgrounds in chemistry to collect high-quality carbon-system data, providing essential quantitative context for their ocean acidification research. The sensor will be a compact, relatively low-cost, robust instrument designed to collect pH, total dissolved inorganic carbon, and total alkalinity data from discrete samples, shore-based stations, and a variety of surface platforms.

The specific objective of this proposal is to develop a third-generation "Multi-parameter Inorganic Carbon Analyzer" (MICA III), which will enable straightforward measurements of dissolved inorganic carbon (DIC), total alkalinity (TA), and pH in the field. This multi-parameter sensor will be easy to operate and highly portable, with virtually no supporting infrastructure requirements. The underlying carbon system measurement protocols were previously demonstrated in the field using MICA I. DIC and pH will constitute the fundamental pairing from which other parameters (the partial pressure of CO2, TA, and carbonate ion concentration) will be calculated. An additional directly measured parameter (TA) will allow assessments of internal thermodynamic consistency among our calculated and measured properties. To enable TA measurements within a compact instrument, the investigators will use a novel equilibration design as an alternative to the standard titration methods. With this approach, they plan to substantially simplify the instrument, eliminating requirements for highly precise acid metering. State-of-the-art optical, mechanical, and electrical design software will be employed in conjunction with laboratory and field tests, using an iterative approach to develop and refine the design of MICA III over a three-year period. Field data and associated metadata collected during this effort will be submitted to the Biological and Chemical Oceanography Data Management Office, which will also archive the data in the appropriate national archive facility.