Reconstructions of Holocene climate variability in Alaska from a number of proxy records indicate that dramatic climate shifts have occurred on centennial to millennial time scales. Understanding the timing, magnitude, and geographic extent of these climate fluctuations and the dynamic response of glacier systems is essential to assessing models of predicted environmental change due to observed modern warming. We investigated the age and field relationships of deposits associated with Holocene advances of the Castner Glacier in the Central Alaska Range. Efforts to map and date the moraines at this location and at the adjacent Canwell Glacier have been undertaken since 1950’s, but have yielded limited and in some cases inconsistent results (Reger and Péwé, 1991). This study builds on those previous efforts. New and refined field mapping of surficial deposits has identified three distinct moraine complexes beyond the current margins of the Castner Glacier, denoting at least three separate Holocene advances of progressively more limited extent.

We are applying multiple dating methods to constrain the ages of these moraines, including terrestrial cosmogenic nuclide (TCN) exposure dating, tree ring counting and lichenometry, along with previously obtained radiocarbon and tree-ring data. Lichen diameters were measured on all three moraines to establish the timing of moraine deposition based on a regional lichen growth curve. The published compound-linear growth curve for the Central Alaska Range was used to convert lichen diameters to ages (Solomina and Calkin, 2003). These results, along with tree-ring ages obtained in this study, enable an assessment of previously recorded lichen measurements at the Black Rapids and Canwell Glaciers. Lichenometry-based ages of the two older moraines at the Castner Glacier suggest Neoglacial (3150 ± 150 BP; calendar years before 1950) and early Little Ice Age (770 ± 20 BP; 1160–1200 AD) advances, respectively. The age of the youngest moraine complex was determined using data compiled in previous work, along with new lichenometric and tree-ring data obtained in this study. The date of stabilization of the youngest moraine was determined to be late Little Ice Age (117 ± 10 BP; 1823–1843 AD). TCN exposure-dating of boulders on the Castner Glacier moraines is underway, and is anticipated to further refine this chronology. The ca. 3150 BP advance of the Castner Glacier may be synchronous with documented Neoglacial advances of the nearby Canwell and Black Rapids Glaciers, as indicated by radiocarbon dates previously reported at these latter sites (Reger et al., 1993). The results of this study provide a basis for paleo-ELA reconstructions as a means of inferring climatic conditions during the Neoglaciation of Alaska.

Acknowledgements: This research was supported by the University of New Hampshire Department of Earth Sciences, the John T. Dillon Alaska Research Award from the Geological Society of America, and a Grant-In-Aid of Research from Sigma Xi, The Scientific Research Society.