Research

My Research

I am broadly interested reconstructing redox-sensitive elemental cycles and the role of surface processes in modifying seawater chemistry over the course of Earth history. I have also become interested in expanding the rigorous application of isotope techniques toward problems in the forensic sciences. Below are short descriptions of my past and present research efforts on some of these topics.

Productivity & Organic Matter Preservation

Organic carbon burial is a key control on the accumulation - or depletion - of oxygen within Earth's atmosphere and oceans. Although mineral surface sorption has emerged as a major influence on the ability of organic matter to survive microbial attack and be buried, the detailed effects of such sorption on the abundance and isotopic composition of organic compounds within soils and sediments remain murky. For my postdoctoral research, I plan to investigate the controls on the production of organic matter and its preservation in sediments through a combination of field studies and laboratory experiments. I hope to better understand the kinetics of degradation of different organic matter compounds under various conditions, to evaluate any carbon and hydrogen isotope effects associated with such degradation, and to interrogate the role of mineral sorption in preserving various compounds. Check back here later for updates!

The Ancient Marine Sulfur Cycle

Records of the isotopic composition of sulfate through geologic time have critically informed our understanding of the ancient sulfur cycle - namely, changes in the relative balance of sulfur being removed from the ocean in oxidized (e.g., sulfate) or reduced (e.g., sulfide) forms at different times. However, diagenetic reactions in sediments have the potential to alter these records and obscure signals generated through variations in the sulfur isotopic composition of seawater sulfate. Using a new MC-ICP-MS method that has lowered the amount of sulfur required for precise isotopic analysis by orders of magnitude, I carefully sampled well-preserved regions of brachiopods to recreate the sulfur isotopic record for the Permo-Carboniferous and determine how robust the existing, potentially altered record may be. This work was recently published in Earth and Planetary Science Letters at the below link:

https://doi.org/10.1016/j.epsl.2020.116428

Deep Ocean Pyrite Burial in the Modern Marine Sulfur Cycle

The sulfur cycle exerts a key control on the concentration of oxygen in Earth's atmosphere. However, several aspects of the modern sulfur cycle remain poorly constrained. Part of my thesis is focused on better understanding the cycling of sulfur in oxygenated deep ocean settings. These regions - in particular, the continental slope and rise - have been understudied relative to the sites on the continental shelf, but are estimated to encompass around half of the globe's net sulfate reduction. Using pore waters and sediments collected from deep ocean regions on International Ocean Discovery Program (IODP) Expeditions 361 & 363, I have been measuring the concentration and sulfur isotopic composition of various sulfur-bearing phases to determine the characteristics associated with sulfur cycling at these sites with the aid of diagenetic models. My results will have important implications for the sulfur isotopic composition of sulfide minerals buried globally, a crucial parameter in box model reconstructions of the ancient sulfur cycle.

Oxidative mixing and reworking of sediments by storms has the potential to effect the sulfur isotopic composition of sulfide buried in shallow marine sediments, but has also been understudied. For my undergraduate thesis, I examined the effects of oxidative reworking on the isotopic composition of sulfate and sulfide in carbonate-rich sediments using a series of sediment columns constructed with mud collected off the coast of Florida. My results suggested that burn-down of labile organic matter and a corresponding decline in sulfate reduction rate is associated with a larger isotopic difference between sulfate and sulfide. This relationship had previously been observed in laboratory cultures of sulfate-reducing microbes, but had not been demonstrated in the lab with natural sediments containing diverse microbial populations. The results of this project were presented at the 2014 AGU Fall Meeting.

Glaciers in the Past

Understanding the extent of glaciers at different times during Earth history is important for climate records, especially for untangling the effects of temperature and ice volume on the oxygen isotopic composition of marine carbonates. However, the erosive nature of glaciers often results in the destruction of evidence of previous glaciations by more recent ones. The provenance, or place of origin, of sediments eroded and deposited by glaciers may provide clues regarding past glacial extent. As an undergraduate summer intern at Lamont-Doherty Earth Observatory in 2012, I researched the potential for K-Ar ages to serve as a provenance indicator for the fine (< 63 micron) fraction within Southern Ocean sediments. My results suggested that K-Ar ages may serve as a valuable provenance proxy for terrigenous provenance in regions proximal to terranes with disparate geologic histories. The results of this study were presented at the 2012 AGU Fall Meeting.