OCEANIC MEASUREMENTS OF TOTAL ALKALINITY
Link to NOAA Strategic Plan: NOAA’s Mission Goal 2: Understand Climate Variability and Change to Enhance Society’s Ability to Plan and Respond
RESEARCH OBJECTIVES AND SPECIFIC PLANS TO ACHIEVE THEM
High quality surface alkalinity data is an integral part of current oceanic carbon cycle science. In particular, it is an essential part of the current method used for the estimation of anthropogenic CO2 in the ocean. Here, it is used in two contexts: it is used as a reference level for inferring changes in alkalinity since a water parcel left the surface, it is also used as the basis for estimating the preindustrial total CO2 content of a parcel of ocean water by calculating this value from the surface alkalinity and a p(CO2) value of 280 µatm. The uncertainty of our present data set for alkalinity compromises the sensitivity of these calculations. This project has two key thrusts:
1. Improvement of the measurement technique for alkalinity by developing a spectrophotometric-based end-point detection technique for both at sea, and for shore-based measurements.
2. The accumulation of a high-quality global data set for the distribution of total alkalinity in the surface waters of the global oceans. This is being achieved by shore-based laboratory measurements of alkalinity on samples collected on a variety of international oceanographic cruises.
RESEARCH ACCOMPLISHMENTS
1. Preparation of a manuscript detailing a rigorous assessment of the sources of uncertainty involved in the determination of alkalinity using an open-cell titration (to be presented at BERM-11 meeting, November 2007).
2. Rewrite of LabVIEW software used to control open-cell alkalinity titrations so as to allow use of modern computers, and to make future upgrades more manageable.
3. Development of appropriate algorithms that enable the use of an indicator dye to locate the end-point in an alkalinity titration. It appears that it may be practical to do this without making a special effort to control the titration temperature, thus significantly simplifying the procedure. This still needs to be verified experimentally.
4. Completed the analysis of a wide variety of samples in the laboratory. These include samples collected from the equatorial Pacific on the NOAA ship R/V Ka’imimoana, as well as a variety of samples obtained from other parts of the world (predominantly the Atlantic Ocean). Data currently being checked to ensure it is archived appropriately.
