Tree-ring measurements as a proxy of glacier mass balance at Mount Baker, Washington, USA

O'Neal, Michael A.A 243-year mass balance record was reconstructed for Easton Glacier at Mount Baker, Washington, USA, using annual ring-width measurements of mountain hemlock tree cores. Tree cores were collected on the lateral moraines of Easton Glacier and were measured and analyzed to create a site tree-ring chronology. The tree-ring chronology presented in this study responds to the same climatic forcings as glacier mass balance, mainly wintertime precipitation and summertime temperatures, providing validation for our linear regression model which uses the tree-ring chronology to reconstruct glacier annual net mass balance. Transformations were tested and applied to the data to improve the performance of the model, and a final mass-balance record for Easton Glacier and a regional index were created and analyzed for the period of AD 1770-2012. The final Easton Glacier and regional reconstructions explain 48% and 42%, respectively, of the variance in the mass balance data. Periods of above-average mass balance of Easton Glacier were identified between AD 1800-1820, AD 1845-1853, AD 1893-1927, and AD 1952-1985. Periods of predominately below-average mass balance were shown between AD 1780-1800, AD 1834-1844, AD 1884-1892, AD 1928-1951, and AD 1985-2005. Our record is consistent with known dated moraine positions and with other proxy records in the surrounding region. It also corresponds well with positive and negative phases of the Pacific Decadal Oscillation, emphasizing the influence of wintertime precipitation variability on the mass balance of glaciers in the North Cascades.University of Delaware, Department of GeographyM.S