Unfiltered grain set with orientation of ALHIC1901_234_2

This study is currently utilizing Scanning Electron Microscope Electron Backscatter Diffraction (SEM EBSD) to conduct high resolution maps of ice crystal structure across samples from the bottom 25 meters of Allan Hills ice core (ALHIC) 1901,which locally contains evidence of elevated carbon dioxide and particulate matter concentrations. SEM EBSD allows for characterization of physical properties, such as grain sizes, grain shapes, crystal orientations, and dislocation density as well as misorientation within grains and between grains. Initial work has found evidence of pervasive grain boundary migration and grain growth but also significant grain-size variability along the core with the deepest sample directly adjacent to bedrock with the notably smallest grain size. Bubbles occur at grain boundaries, triple junctions, and, more rarely, apparently isolated within large grains. The presence of bubbles at grain boundaries and triple junctions has been proposed as a potential mechanism for inhibiting grain growth. Some notable differences between sample maps across different depths include changes in misorientation densities that may be indicative of changing deformation mechanisms. 

This study investigates small scale variations of trace gases in ALHIC1901 along depths of 155.065 to 155.355 m which correspond to an age range of approximately 1.37 to 1.60 million years and is located 5 meters above bedrock. Carbon dioxide and methane concentrations were analyzed using gas chromatography at 2 cm resolution. Isotope ratios of water were also analyzed using laser spectroscopy. Initial multitrack electrical conductivity measurements (ECM) were done along the long face of the ice core samples revealing distinct boundaries of high and low conductivity suggestive of layering or a fold of bedrock material. Preliminary results show a positive correlation between high conductivity and layers of elevated impurities with higher CO2 concentrations. This trend was significantly more pronounced in CO2 concentration measurements compared to CH4 concentration measurements across depth. Further work is being done to model carbon dioxide diffusion and potentially constrain time scales of diffusion, as well as measure carbon isotope ratios in CO2. Ultimately this study will allow us to better understand influences on pristine greenhouse gas preservation in ice cores. 

Dry extraction for CO2 measurements in ice at Oregon State University

Coulter Counter instrument for dust mass concentration and grain size distribution measurements at Scripps Institution of Oceanography

Previous analysis of dust concentration and size distribution in ice cores have been limited to the past 800 ka; however, the Allan Hills Blue Ice Area (BIA) in East Antarctica provides a unique opportunity to examine older discontinuous ice between 500–4000 ka. Ice core samples from the Allan Hills were analyzed for eolian dust and basal particulate matter concentration in the size fraction 1–30 μm using a Coulter Counter. Preliminary results reveal a positive correlation between mass concentration and depth in the ice located 10 meters above the bedrock and below, indicating the influence of a basal sediment imprint. For shallower ice above this threshold, the majority of the dust mass concentrations are less than 200 ppb, which is characteristic of an interglacial period for a coastal ice core. This implies that there is better preservation of ice at this BIA during interglacial periods when snow accumulation is higher. This study is the first to report measurements of dust in ice exceeding 800,000 years, providing crucial data for understanding past environmental dynamics and basal ice-rock interactions.

During the Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) campaign in summer 2023, high frequency trace gas measurements as well as flask measurements of Δ14C were conducted aboard the NASA DC-8 airborne platform across major cities in North America including Los Angeles, New York City, Toronto, and Chicago. Combining these data streams to develop maps of proxy-based high-frequency fossil fuel and biogenic CO2 for these major urban areas showed significant contributions of fossil fuel and biospheric emissions in all cities, with NYC and Chicago having significantly higher biogenic contributions and LA having much greater fossil contributions. Additionally, high-frequency fossil CO2 data was used to evaluate the GReenhouse gas And Air Pollutants Emissions System (GRA2PES) inventory. GRA2PES emissions was used as input to the high-resolution WRF model, allowing us to compare simulated GRA2PES based fossil fuel CO2 with our high-frequency observed fossil fuel CO2 data along the AEROMMA flight tracks."  This evaluation of the GRA2PES inventory across multiple large North American cities is informative of the accuracy of publicly reported emissions data and help improve “bottom-up” inventory emissions estimates. 

Pseudo high frequency fossil fuel CO2 mapped in Los Angeles on 8/25/23

Marine strontium (Sr) isotope values are a useful geochronological tool because they allow us to correlate sedimentary rocks not suitable for the application of other geochronometers. This allows us to correlate geochemical information across sedimentary basins to develop a broader understanding of the geochemical record of the rise of atmospheric oxygen levels in the Paleoproterozoic ~2.4-2.0 billion years ago. Sr isotope values in marine carbonates record global seawater chemistry at the time of deposition because Sr is well mixed in the ocean. This project determined Sr isotope values of marine carbonates from a previously dated succession of rocks from the Francevillian Basin in Gabon, which will allow linkages of this succession more broadly across the basin. This will represent a crucial step towards identifying the main drivers of the end Lomagundi Jatuli carbon isotope excursion  in the Francevillian Basin.

Rb-Sr ion exchange chromatography columns