Why is some organic carbon preserved for long timescales?
Throughout Earth history, atmospheric oxygen rose sharply at times but has otherwise been stable for long periods. An ambitious, long-term goal of my research plan is to how and why this occurred. Oxygen accumulation requires that some organic carbon escapes respiration and is geologically preserved. However, the mechanisms that control preservation remain unknown.
To assess organic carbon age and molecular structure, I developed a thermo-analytical tool and the corresponding theoretical framework for interpreting resulting data. Using this tool, I am building a unifying, mechanistic theory of how organic carbon is preserved; I propose that physical protection by particles promotes preservation by increasing the diversity of chemical bonds. Follow-up, bench-top experiments will test this theory with new mineralogical, molecular, and isotopic techniques. For example, I will assess if changes in sediment mineralogy, driven by mountain building and floodplain weathering, impact organic carbon preservation due to physical protection.
How does pyrite oxidation regulate atmospheric oxygen?
In addition to organic carbon burial, the oxidation of iron sulfide minerals such as pyrite during mountain exhumation and weathering is a dominant pathway that controls the long-term evolution of atmospheric oxygen content. However, like organic carbon preservation, the mechanisms that control pyrite oxidation rates and corresponding oxygen consumption remain under-constrained.
I have recently incorporated a suite of bench-top pyrite weathering experiments to better constrain oxidation rates, the oxidants involved, and the resulting isotopic signature of pyrite oxidation. Coupled with these experiments, I measure the oxygen minor isotope composition of resulting sulfate, since these signals can be preserved in geologic archives and can thus give us a window into pyrite oxidation fluxes throughout Earth history.