UC San Diego

Accurately measuring the marine CO2 system is imperative to assess the effect of oceanic uptake of anthropogenic CO2 and the consequences for marine biogeochemical processes. CO2 in the ocean is both a gas and an acid, so it is necessary to measure at least two parameters describing its chemistry, where two of the most commonly used parameters being pHT and total alkalinity (AT). While both are fairly straight forward to measure and have a long history in oceanography, they have unique challenges that can greatly reduce their quality for use in CO2 system calculations. For pHT measurements, especially electrometric methods involving a liquid junction, it is crucial to calibrate the measurement using a buffer prepared in a solution similar to seawater. Chapter 2 of this dissertation describes a method to prepare 0.04 mol kg-H2O−1 equimolar buffer 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS)-TRIS·H+ in synthetic seawater. Its point of success is using a simple methodology that is also reproducible, and produces a buffer with a pHT within 0.006 of the assigned value 8.094 (at 25 °C). The measurement of AT and even its definition is simple, being the balance between bases and acids in seawater and measured by titration with acid. To use AT in CO2 system calculations, it is necessary to account for the non-carbonate alkalinity components. While most if not all inorganic bases and acids have been identified and can be accounted for, for decades there has been evidence for unidentified, likely organic, bases present at significant levels. Little advance has been made in understanding the alkalinity contribution from component “X” (AX) due to a lack of an unambiguous measurement. Chapter 3 describes an unambiguous, open-cell titration method to measure AX, which includes an uncertainty assessment informed both by ancillary measurements and by titration simulations using a custom chemical equilibrium model. Chapter 4 shows the success of this this titration method using a combination of well-characterized simple salt solutions and a simple seawater solution, by themselves and with the addition of one or two simple organic, proving that the system is capable of measuring AX at 3.4 micromol kg–1.