The ocean plays an integral role in the global carbon cycle and serves as the largest planetary reservoir for carbon. As more anthropogenic CO2 is released to the atmosphere it is essential to understand and quantify the impact of elevated pCO2 on the ocean’s role in the uptake, transfer, and transformation of carbon as well as cascading effects on biogeochemical processes. Direct observations are limited in space and time due to shortage of autonomous technology available to effectively monitor the aqueous carbon dioxide system at seasonal, interannual, and longer timescales. This dissertation describes novel sensors that are being developed and implemented to expand available marine biogeochemical observations.

The first two chapters describe the development of a solid state sensor capable of rapid and simultaneous measurement of pH and Total Alkalinity of seawater for monitoring the aqueous carbon dioxide system. This novel sensor requires no external reagents, has low power consumption, and meets the rugged demands required for integration with autonomous platforms. Chapter 1 focuses on the development and analytical assessment of the working sensor. Chapter 2 provides a more detailed description of all the processes and methods that were explored in reaching the working sensor described in Chapter 1.

Chapters 3 and 4 both use profiling floats equipped with existing biogeochemical sensing technology deployed through the Southern Ocean Carbon and Climate Observations and Modeling project to look at biogeochemical processes in the Southern Ocean. SOCCOM is a pilot program that will hopefully lead to global scale array of biogeochemical sensors on profiling floats. In Chapter 3, the influence of sea ice on the relative role of physical versus biological components of the pH and O2 signal is explored. While Chapter 3 primarily focuses on organic biogeochemical processes, Chapter 4 focuses on the role of CaCO3 reactions in the Southern Ocean carbon budget.

Declines in amphibian populations have been reported throughout the world in recent years. Chytridiomycosis, a disease of amphibians caused by the chytrid fungus, Batrachochytrium dendrobatidis, is one of a number of factors that have been shown to contribute to these population declines. B. dendrobatidis is associated with rapid population declines and local extinctions of populations of mountain yellow-legged frog, Rana muscosa, in some areas of the California Sierra Nevada mountains, however in other areas R. muscosa populations are persisting in the presence of this fungal pathogen. We conducted field surveys and laboratory experiments to investigate several factors that may explain these different population-level outcomes of B. dendrobatidis. Our field surveys revealed that R. muscosa at persistent sites are carrying very low fungal loads, which lead to sub-clinical infections. At these sites, B. dendrobatidis is having no detectable effect on adult R. muscosa survival (although subadults may be experiencing high disease-induced mortality), and some adults are apparently losing the infection. At sites experiencing frog population crashes, a large fraction of R. muscosa adult are carrying extremely high fungal loads, and very few infected adults are surviving over the course of a summer, or between years. We found no consistent differences in temperature profiles between the two types of sites. Our laboratory experiments detected no difference in transmission rate or virulence of fungal strains from persistent versus die-off sites. We are investigating differences in susceptibility of frogs from the two types of sites in an experiment currently underway.