METHODS WATER ISOTOPE DYNAMICS OF THE JUNEAU ICEFIELD Paloma Siegel 1,2 , Bradley Markle 1,3 1 Stable Isotope Laboratory, Institute of Arctic and Alpine Research 2 Department of Geography, University of Colorado Boulder 3 Department of Geological Sciences, University of Colorado Boulder RESEARCH OVERVIEW The Juneau Icefield is situated on the Southeastern Coast of Alaska, 1800m above the Pacific Ocean. Recent research has revealed that the glaciers in Southeast Alaska are retreating at some of the quickest rates globally (Zemp et al., 2019). This research examines the 2019 Matthes-Llewelyn Ice Core drilled on the Juneau Icefield to understand water isotope composition changes throughout ice depth in a temperate glacier. Data anomalies were revealed in the top 24 meters of the core, where the firn-ice transition was reached, and a firn aquifer identified. Is liquid water stored within the glacial ice altering the isotope values post depositionally? We examine spatial and stratigraphic trends, as well as climate modeling with the Simple Water Isotope Model (SWIM) and NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT). MELTWATER EXAMINATION: POST-RAINFALL EVENT DISCUSSION / FUTURE WORK Drivers of Matthes-Llewelyn Ice Core anomalies: ● Post-depositional processes (most probable) ● Changes in evaporation source temperature Future work will help to clarify which of these drivers might be responsible for the shifts in isotope values, including: ● Back trajectory analysis to evaluate if the evaporation temperatures indicated by the model are plausible over the top 24m of the core. ● Repeat ice core at the Matthes-Llewelyn divide in order to collect higher resolution data and investigate the presence and size of the identified 2019 firn aquifer. ● Ice lens analysis to examine possible isotopic differences between ice lenses and surrounding snow. If changes are consistent, what is the trend and how does it compare to 2019 core anomaly? ACKNOWLEDGEMENTS Research overseen by Bradley Markle, PhD, assistant professor at the Institute of Arctic and Alpine Research Stable Isotope Lab and in the Department of Geological Sciences at CU Boulder , as well as the assistant academic director of the Juneau Icefield Research Project . Dr. Markle has also managed this project since 2012, when the spatial analysis began. Isotope data since 2012 has been analyzed in the field and at the University of Alaska Fairbanks by Eric Klein. Data collection and analysis was made possible by the student research team; Liam Kirkpatrick (Dartmouth College), Michela Savignano (Brown University), Abby Holt (Principia College), and Nicholas Bakken-French (Whittier College). Funding for this project has been received from the Undergraduate Research Opportunities Program at CU Boulder and the Foundation for Glacier and Environmental Research. 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Mathematical and Physical Sciences , 239 (1216), 113–133. https:/ /doi.org/10.1098/rspa.1957.0026 Zemp, M., Huss, M., Thibert, E., Eckert, N., McNabb, R., Huber, J., Barandun, M., Machguth, H., Nussbaumer, S. U., Gärtner-Roer, I., Thomson, L., Paul, F., Maussion, F., Kutuzov, S., & Cogley, J. G. (2019). Global glacier mass changes and their contributions to sea-level rise from 1961 to 2016. Nature , 568 (7752), 382-386,386A-386L. http:/ /dx.doi.org/10.1038/s41586-019-1071-0 Background photo: Nicholas Bakken-French Group Sites Samples Shallow Core 6 131 Snow Pit 10 142 Surface Transect 6 84 2019 Deep Core 1 330 Other 2 2 Total 25 689 CLIMATE MODELING AND PRELIMINARY RESULTS Simple Water Isotope Model (SWIM): For given climate parameters and isotope values, SWIM reconstructs three temperature records: 1) evaporation source temperature, 2) condensation site temperature, and 3) condensation surface temperature (Markle & Steig, 2021). Model suggests anomalies are due to changes in moisture source location (evaporation temperature) but does not account for post depositional processes occurring in the snow. Samples were measured using a Picarro L2130 cavity ring-down laser spectrometer (Picarro, 2021). Figure 2: Temperature reconstructions of the Matthes-Llewelyn Ice Core given by the SWIM model. Output suggests that evaporation source temperature (T source ) is the driver of anomalous data in upper 24m. Figure 4: Core estimated 150-300 years old (Figure: Liam R. Kirkpatrick, University of Washington) 2021 Sample Sites Key anomaly: firn aquifer at 24 meters. What processes are driving this change? Figure 6: Resample of Pit TKG4 7 days after consistent rainfall. D xs values begin to deviate after 250cm in depth from snow surface. Figure 3: 2019 Core isotope data with firn aquifer sample. D xs value indicates potential fractionation as driver of 24m observed anomaly. Matthes-Llewelyn Ice Core Firn Aquifer Values 2019 Matthes-Llewelyn Ice Core Isotope Record Figure 1 : Matthes-Llewelyn isotope data plotted versus depth. Visible in all three plots are large spikes around 24m below the surface, where a firn aquifer was identified. Firn Aquifer Firn Aquifer Anomaly PR4 Transect Before and After Rainfall TKG4 Pit Before and After Rainfall Figure 5: Resample of Transect PR4 7 days after consistent rainfall. D xs are shifted up in general, but are not necessarily indicative of post-depositional change. Before rainfall: 7/6/21. After rainfall: 7/15/21 Other Drivers of Isotope Value Change: - Surface Melt - Ablation - Original snow perhaps not present anymore - Precipitation mixing D xs Shift Below 250cm: - Liquid water accumulation at or near density changes in the glacier - Potential due to post-depositional processes