PhD Student Earth Sciences
308A Heroy GL
PhD Student Earth SciencesAdvisor: Chris Junium
The bulk of my research is centered on organic molecules known as porphyrins. Porphyrins are the geologically stable diagenetic products of chlorophylls, and hold the potential to unlock a wealth of information about past environments and ecology. Chlorophyll derivatives, including porphyrins and chlorins, have a wide array of applications as molecular biomarkers, redox indicators, and as paleoclimate descriptors. Porphyins and chlorins have also demonstrated their utility as proxies for the ancient nitrogen cycle. Currently, there are a number of outstanding issues in the field of porphyrin-based nitrogen cycle studies, as well as a number of novel prospective avenues to which they could be applied. The goals of my research are to address some of these issues/potential applications, as well as focus them on a specific time interval, the Frasnian-Fammenian biotic crisis.
Porphyrins have the potential to retain specific structural components that are direct indicators of the types of chlorophylls that they are derived from, which can in turn be used to infer the type of organism that they were produced by. For example, Green Sulfur Bacteria are the only currently known organism to produce Bacteriochlorophyll d, which has a characteristic extended side chain at the carbon 7 position. This extended side chain (the tert-butyl group on the top right corner of the porphyrin shown below) is easily identifiable in porpyrin mass spectra, and is unequivocal evidence for Green Sulfur Bacteria being present at the time a given shale was deposited. Furthermore, since GSB can only thrive under euxinic conditions (no oxygen and high levels of sulfide) and are photosynthetic, their presence is indicative of euxinic conditions within the photic zone of whatever body of water the organic matter is derived from.
Nitrogen isotope studies:
The central tetrapyrrole ring of the porphyrin structure contains four nitrogens that contain a primary signal of the nitrogen isotopic composition of the organism that produced it. By analyzing this composition, as well as the composition of the bulk organic matter, various things can be determined regarding the state of the nitrogen cycle in the past, such as the dominant mode of nitrogen consumption, as well as the primary class of organisms that was producing the organic matter.
Frasnian-Fammenian Biotic Crisis:
The Late Devonian was a period emphasized by intense climatic and ecological change, specifically, the rise of land plants, a pronounced decrease in atmospheric CO2 levels from a background of 4000ppm to ~1000ppm by the latest Devonian, intense and widespread tectonic activity and the Frasnian-Fammenian biotic crisis. The Frasnian-Famennian (FF) biotic crisis is ranked within the top six mass extinctions in ecological severity and was particularly devastating to shallow water tropical faunas and reef systems. This particular crisis was also somewhat unique in the respect that it was characterized by multiple ‘pulsed’ extinction events, and only mildly (relative to other mass extinctions) elevated extinction rates coupled with depressed origination rates. I plan to use the aforementioned techniques to study this particular time interval and potentially help characterize the climatic conditions responsible for the biotic crisis.