Undergraduate Honors Theses

Thesis Defended

Spring 2019

Document Type


Type of Thesis

Departmental Honors


Geological Sciences

First Advisor

Boswell Wing

Second Advisor

Sarah Hurley

Third Advisor

Jeffrey Cameron

Fourth Advisor

Charles Stern

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.


The evolution of oxygenic photosynthesis and the resulting accumulation of oxygen in the atmosphere, known as the Great Oxidation Event (GOE), is one of the most prominent transitions in Earth history. While cyanobacteria are thought to be responsible for the accumulation of oxygen during the GOE, the timing of the evolution of oxygenic photosynthesis, and the abundance of different primary producers during this time remains unconstrained. The carbon isotopes provide a continuous record through this time period and may be a way to investigate the dominant primary producers during this time. In order to interpret the geologic carbon isotope record or the offset between preserved carbonate rocks and synchronous organic carbon (εTOC), we need to understand the underlying carbon isotope fractionation by primary producers (εP). Here we investigate the influence of CO2 concentration and the growth rate on carbon isotope fractionation by four cyanobacterial strains. Under light-limiting conditions, we find a single relationship between εP values and growth rate across all strains. Our results suggest that carbon isotope fractionation by cyanobacteria is not strain-specific, but is instead controlled by underlying physiology. These results support the use of εP values as a proxy for unicellular cyanobacteria. Further work is necessary to understand the factors influencing εP values in different conditions and to understand how εP values relate to the geologic carbon isotope record.

Available for download on Saturday, April 11, 2020