Geophysical Reconnaissance to Expand Ice Core Hydroclimate Reconstructions in the Northeast Pacific

Generally, this award aims to explore hydroclimate changes over the past Millennium that possibly occurred in response to changes in the mean state of the El Nino-Southern Oscillation (ENSO). By advancing the development of a spatial-temporal network of ice core accumulation records covering the past millennium in the NE Pacific region of the United States, this research will foster a greater understanding of regional hydrologic response to the coupled ENSO system. The researchers propose to investigate the hypothesis that a change occurred from a persistent La Nina-like state during the Medieval Climate Anomaly (MCA) to a persistent El Nino-like state during the Little Ice Age (LIA). The research team will test this hypothesis by reconstructing and evaluating the spatial precipitation anomaly pattern in the Northeast Pacific across the MCA-LIA transition. Their hypothesis is founded on modern observations that show an enhanced (weaker) coastal-inland precipitation gradient in the region during La Nina (El Nino) conditions. The researchers predict that the NE Pacific precipitation anomaly pattern will weaken across the MCA-LIA transition. The project will support an early career scientist, provide support for undergraduate and graduate students, and enable outreach to K-12 teachers and students through the PolarTREC program, an NSF funded program which seeks to link K-12 teachers with Polar researchers with a goal of integrating polar science research into K-12 curriculum. The potential return on investment of the proposed science is high in terms of advancing the state of knowledge in this area of science and the support of early career scientists and outreach aspects of the proposal are important to the NSF Mission and mandate. For the past decade, the researchers have been developing an ice core array in the NE Pacific of the United States that targets the two nodes of this precipitation dipole (i.e., St. Elias Range and Central Alaska). The most recent ice core acquisition was in 2013 with the recovery of two surface-to-bedrock 210-meter ice cores from Mt. Hunter in Denali National Park. To determine precipitation variability at the Mt. Hunter site over the past millennium, the researchers will rely on a suite of supporting geophysical data to constrain glacier geometry, velocity, boundary conditions, and rheological properties in a 3-dimensional finite element numerical model. The combined observational and model datasets will allow the team to remove influences of ice flow (which causes layer thinning) and spatial variability in snow accumulation rate to estimate temporal accumulation variability from the two ice cores. In contrast to Mt. Hunter, little is known about the geophysical characteristics of the coastal St. Elias Range ice core sites (PR Col, NW Col, King Col on Mt Logan and the Eclipse Icefield), which were drilled in 2002 prior to recent advances in geophysical techniques and numerical modeling capability. This lack of information would introduce error in any comparison of the St. Elias and Mt. Hunter accumulation records, and thus evaluation of the MCA-LIA transition hypothesis. Consequently, the research team specifically proposes to improve ice core-based accumulation records, and therefore hydroclimate reconstructions for the past millennium, in the NE Pacific through the collection of new geophysical data at existing ice core sites in the St. Elias Range. The science objectives are to: 1) develop bedrock topography maps of the Eclipse Icefield, King Col, and Mt. Logan summit plateau sites; 2) determine surface velocities at all sites; 3) map near-surface spatial accumulation rate patterns; 4) trace internal isochrones at all sites; 5) estimate ice deformation effects on layer thinning; 6) produce updated, to 2016, and corrected accumulation time series at all sites; and 7) compare corrected accumulation records from the Mt. Hunter and St. Elias sites to evaluate spatial precipitation patterns over the past millennium. The research strategy necessitates the use of state-of-the-art ground penetrating radar (GPR), geochemical, satellite remote sensing, numerical modeling, and data synthesis techniques.