INVESTIGATING BLUE LIGHT INTENSITY AS A NEW PARAMETER FOR TREE RING-BASED GLACIER MASS BALANCE RECONSTRUCTIONS IN ALASKA

Tree ring-based glacier mass balance reconstructions aim to extend records back in time to more fully analyze variability and better identify potential forcings. The current 40 to 50-year observational mass balance records in western North America are dominated by ablation and document a rather narrow span of a much longer glacial history. Traditionally, reconstructions based on tree-rings have been conducted using ring width (RW) or maximum latewood density (MXD) parameters. However, an additional and newly developed proxy, blue light intensity (BI), reflects lignin content in latewood tree growth and demonstrates a strong, high frequency signal for temperature in the warmer months along the Gulf of Alaska (GOA). This new BI parameter together with conventional RW data, was compared with seasonal and annual mass balances at two USGS Benchmark Glaciers, the coastal Wolverine Glacier and the more interior Gulkana Glacier in southcentral Alaska.

Comparisons of total, summer, and winter mass balance with BI and RW chronologies show that a combination of the parameters can more fully reconstruct past mass balance. Included in the development of these models is the assessment of how local and regional climate variability is captured in single and composite chronologies. Preliminary results for Gulkana Glacier suggest that the regional BI chronology is most strongly correlated with summer mass balance, more so than for RW. Additionally, Wolverine Glacier’s summer and annual mass balance correlate best with regional chronologies that likely capture more of the large-scale circulation changes. Ongoing investigations aim to examine the use of tree-ring records that are teleconnected to the climate variability at the Alaska sites. Previous work has shown that teleconnection is responsible for an inverse relationship between mass balances of the Alaskan glaciers with the glaciers of the Pacific Northwest at least on the decadal scale and his relationship may be leveraged in modeling and reconstruction.