UC San Diego

Carbon in the earth system has gained immense relevance to modern society, and understanding the controls on and impacts of rising carbon dioxide (CO2) in the atmosphere is central to humans’ social well-being in the years to come. Predicting future changes requires both global-level knowledge of sources and sinks of CO2 to the atmosphere and local-level information about individual ecosystems’ responses to changes in environmental conditions thus far. This dissertation addresses three components of the greater effort to understand and predict impacts on the earth system of rising CO2. In the first chapter I explore whether the atmospheric CO2 record since 1900 can be used to better estimate the source of CO2 from land use and land cover change to the atmosphere when accounting for uncertainties in the other global sources of sinks of CO2 (e.g., fossil fuel emissions, terrestrial and marine drawdown and release of CO2) thus far. I show that the atmospheric CO2 record favors land use and land cover change CO2 flux estimates with lower decadal variability and can potentially highlight erroneous features in some published estimates. Further, we resolve a downward correction to the land use flux mean since 1900 across 20 published estimates of 0.35 PgC year−1 to 1.04 ± 0.57 PgC year−1. The second chapter combines observations of seawater organic and inorganic carbon in two coral reef ecosystems to add resolution to our snapshot of two coral reef systems’ biogeochemistry under current climatic conditions. The study presents the first inorganic carbon isotope measurements collected on a coral reef in Okinawa and finds that the reef has a community fractionation factor between -13.4 and -11 ‰ during organic matter fractionation. Finally, the third chapter presents the framework for a method to make fast and precise measurements of seawater dissolved inorganic carbon, which is one of the primary parameters used to quantify changes in the ocean stemming from marine biogeochemical processes and rising atmospheric CO2. This chapter shows that the developed method is capable of achieving high-precision measurements and can be calibrated, and the chapter identifies possible limitations to overall measurement precision.