UC San Diego

The ocean's sequestration of anthropogenic carbon dioxide has major consequences for global change. Not only does it temper global warming by removing some of the greenhouse gas from the atmosphere, it also results in ocean acidification through the reaction of CO₂ and H₂O. While the environmental science community is well aware of these issues at a broad, global level, there are notable gaps in our understanding of changes occurring over smaller spaces and shorter times. This dissertation describes novel tools that are being developed and implemented in order to fill those gaps. Specifically, it focuses on autonomous, in situ systems designed to quantify total dissolved inorganic carbon (the sum of all chemical species formed in seawater directly through the addition of CO₂ to H₂O) and pH (a measure of the proton concentration in seawater. The first two chapters describe a "Micro-Rosette" for microfluidic quantification of total dissolved inorganic carbon (DIC) from profiling floats. Chapter 1 deals specifically with optimization of a gas diffusion cell, an integral component of any liquid-to-liquid (i.e., seawater to receiving solution) DIC extraction technique. 109 unique combinations of gas diffusion cell geometry, seawater volume, and diffusion time were tested to rigorously determine the optimal conditions needed in order to quantify DIC repeatably. Chapter 2 incorporates these findings and implements a sixteen-sample microfluidic collection manifold such that seawater can be captured and stored as a profiling float ascends from 2000 m to the surface and subsequently analyzed once the float returns to its "park depth" (̃1000 m), where it remains for over a week. Chapter 1 achieves better than 0.2% repeatability in DIC measurements; the multiplexed collection and analysis in Chapter 2 attains 1%. Chapters 3 and 4 pertain to in situ measurement of seawater pH with the Honeywell Durafet. Well over 100 packages implementing the Durafet have been deployed globally; Chapter 3 lays out best practices for utilizing those packages and validating the resulting data by comparing sensor results to discrete samples and thermodynamically and empirically- derived pH values. Chapter 4 illustrates the use of a Durafet packaged specifically for mobile platforms and surface pH mapping applications