GEOPHYSICAL APPROACHES TO IMPROVE HOLOCENE ICE CORE-BASED HYDROCLIMATE RECONSTRUCTIONS IN THE NORTHEAST PACIFIC

Paleoclimate data from the Pacific basin show significant hydroclimate changes over the past millennium, possibly in response to changes in the mean state of the El Niño Southern Oscillation. One hypothesis invokes a change from a persistent La Niña-like state during the Medieval Climate Anomaly (MCA) to a persistent El Niño-like state during the Little Ice Age (LIA). A test of this hypothesis is to reconstruct and evaluate the spatial precipitation anomaly pattern in the Northeast Pacific across the MCA-LIA transition, because modern observations show an enhanced (weaker) coastal-inland precipitation gradient in the region during La Niña (El Niño) conditions. We therefore predict that the NE Pacific precipitation anomaly pattern will weaken across the MCA-LIA transition. For the past decade, we have been developing an ice core array in the NE Pacific that targets the two nodes of this precipitation dipole (i.e., St. Elias Range and Central Alaska), most recently (2013) with the recovery of two surface-to-bedrock 210-meter ice cores from Mt. Hunter (Denali National Park). To determine precipitation variability at the Mt. Hunter site over the past millennium, we rely on a suite of supporting geophysical data to constrain glacier geometry (including digital elevation models and bedrock topography from ground penetrating radar), velocity, boundary conditions, and rheological properties in a 3-dimensional finite element numerical model. The combined observational and model datasets will allow us 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. Here we focus on our overall approach, and highlight results of terrestrial laser scanning (TLS) conducted on the Mt. Hunter plateau during May-June 2014 with the goals of producing a high precision DEM as input for the glaciological model and evaluating surface elevation change through time.