The Middle Miocene (23-5 Ma) represents a period of rapidly changing climate and active volcanism, particularly in the Pacific Northwest. Our understanding of the structure and composition of plant communities during this timeframe is complicated by a limited or degraded leaf fossil record. Plant fossil assemblages are also often time averaged, representing accumulation of plant material over an extended period. A plant community that was preserved because of a single, short-lived event can provide insight into the composition and structure of that community in life. The Watersnake locality of the Sucker Creek Formation in southwestern Idaho contains two thick (8-14 m) ignimbrite tuffs (volcanic ash layers) that preserve charcoal fragments, reflecting plants that were burned when the tuffs were deposited. In order to identify the woody taxa that made up this community, thin section microscopy is used to examine the preserved cellular detail of the fossil charcoal fragments from the lower tuff. Since ignimbrites are deposited as a part of a single event, the impacts of time-averaging are minimized. Although these deposits reflect a short time, they are likely to integrate across space, providing a view of the broader landscape. The results of this study will reveal the structure of this plant community immediately prior to the eruption that caused the ash flow. I hypothesize that the taxa identified within the ash will be very similar to those of the leaf fossil record found in the shale beds below. A lowland community consisting primarily of wetland Glyptostrobus oregonensis, and Quercus simulata found near flowing water will likely be represented. Upland vegetation consisting of conifers (Pinus, Tsuga) were also likely incorporated into the ash flow as it moved downhill. This study will provide insight into the dynamics of plant community change during the Miocene in relation to volcanic disturbance.

Fire is a fundamental disturbance that drives changes in biome structure. Knowledge of ancient fire regimes may help predict future fire regimes resulting from anthropogenic climate change. Charcoal morphometry (quantified shape of charcoal), particularly charcoal aspect ratio (length:width), is an emerging proxy of ancient fuel type wherein higher mean aspect ratios are associated with grassy fuels. This study aims to experimentally validate this proxy method. Thirty-four modern plant species were sampled from UW Herbarium collections, separating leaf, stem, and reproductive body tissues for each species. Each sample was burned at 500°C for 20 minutes, crushed in a water slurry, and imaged under a binocular microscope. Charcoal particles were enumerated and morphometrics were measured using ImageJ with charcoal particles 125-250 μm and >250 μm analyzed separately to account for differences due to differential particle breakage. Strong evidence was found in the 125-250 μm size fraction through an analysis of variance test (F = 2.66, p = 0.03), that aspect ratio varies as a function of taxonomic group. The strongest evidence for a difference in aspect ratio is found, through Tukey's Honestly Significant Differences to be between graminoid and conifer charcoal (p = 0.03). Evidence is even stronger for a taxonomic effect on aspect ratio in the >250 μm size fraction (F = 3.64, p= 0.007). This variation seems to also be driven by a difference between graminoid and conifer charcoal (p = 0.002), corroborating earlier findings. Future validation of this methodology will be focused on the potential effects of burn temperature and charcoal transport in charcoal morphometric records. Rigorous verification of charcoal morphometry as a proxy of fuel type will help increase confidence in paleo reconstructions of fuel type. 

Nature uses only four nucleobases to store genetic information in DNA. However, additional synthetic bases which use Watson-Crick pairing have been developed and are known as non-standard bases (NSBs). NSBs P, Z, B and S incorporated alongside standard bases A, G, C and T compose DNA strands using a new genetic alphabet. Nanopores offer the potential capability for direct single-molecule sequencing of DNA containing non-standard bases (NSBs). Using a voltage gradient, DNA strands were directed through a nanopore, the biological membrane protein MspA, while we measured the ion current through the pore over time. In studying the effect of NSBs on the ion current through the pore, we observe current measurements corresponding to the Z base have a different noise profile compared to other bases. We hypothesize this noise may be associated with pH-dependent protonation of the base. To test this hypothesis, we conducted experiments with identical sequences in buffers of pH 8 and pH 7, as Z is known to have a pKa of 7.8. I analyzed the noise from the ion current signals to look for signs of protonation. I found increased current noise values associated with the Z NSB in pH 7 compared to pH 8, while the canonical A base had no change in noise values from pH 7 and pH 8, supporting the hypothesis that the increased current noise is due to protonation of the Z base. In addition to indicating potential sensing abilities of nanopores for probing protonation kinetics of DNA, this research contributes to a better understanding of the fundamental mechanisms that control the currents in nanopore sequencing of DNA.