Examining Fine-Scale Greenhouse Gas and Water Isotopic Variability in Shallow Drill Core Samples from the Allan Hills Blue Ice Area

An ice core (CMC1) drilled in 2019 in the Allan Hills Blue Ice Area contains stratigraphically disturbed ice from 500 ka to 2.7 Ma (see S. Shackleton et al., this meeting). We are examining small-scale variability of carbon dioxide (CO2) concentrations, methane (CH4) concentrations and stable oxygen isotope ratios (δ18O) in the lateral and vertical dimensions of pieces of CMC1 ice, each with a discrete 40Ar age, to investigate the scale of variability in these samples as a potential clue to the nature of the stratigraphy. Measurements of CH4 and CO2 were obtained from multiple subsamples of six samples ranging in age from 500 ka to 800 ka. Water isotope data are forthcoming. These ages temporally overlap published greenhouse gas records from other Antarctic cores. Results show a relatively small range of variability in CH4, and CO2 concentrations within each subset, with the standard deviation of subsets ranging from 0.1 ppm to 5.6 ppm for CO2 measurements and 3.1 ppb to 12.3 ppb for CH4 measurements. The mean values of CO2 and CH4 in these samples range from 224 ppm to 254 ppm for CO2 and 471 ppb to 511 ppb for CH4. Ongoing work will investigate the relationships between these variables and existing data for this time period.