TREE-RING-BASED MASS BALANCE ESTIMATES FOR WOLVERINE GLACIER, SOUTHERN ALASKA, A.D. 1554-1987

Climatically sensitive tree-ring chronologies from the Gulf of Alaska are used to provide annual mass balance estimates between A.D. 1554 and 1987 for Wolverine Glacier, southern Alaska. In initial studies, a principle component regression model explains 40% of the variance in the instrumental data recorded by the USGS Benchmark Glacier Program. The reconstructed mean mass balance prior to 1900 is strongly positive, reflecting prominent glacial advances through the middle and late portions of the Little Ice Age. In contrast, mass balance is strongly negative over much of the last century, corresponding with contemporary warming trends. Six pronounced periods of positive and six periods of negative mass balance occur at 30-50 year intervals throughout the reconstruction period. These intervals correspond with regional tree-ring based temperature reconstructions and with PDO regime shifts in the North Pacific. The mass balance model is consistent with dated moraine complexes from Wolverine Glacier based on glacial geologic data providing additional verification. Ongoing analysis will concentrate on model improvement by including tree-ring series from sites within interior Alaska and British Columbia to incorporate more moisture sensitive series. Additionally, efforts are underway to provide tree-ring-based mass balance estimates for other USGS benchmark glaciers in the Pacific Northwest.