35-8 Using Tree-Rings to Reconstruct the 19th Century Thickening of a Glacier at Icy Bay in Coastal Southern Alaska

Session: Ice sheets, glaciers, and landscapes, oh my! (Posters)

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Abstract:

Yahtse-Guyot Glacier advanced 28 km through Icy Bay in southern Alaska during the 19^th century. While the progression of the ice front down-fjord and through the shallow outer bay is well constrained by historical observations and tree-ring crossdates of glacier-killed trees, the timing of ice surface thickening up-glacier of the terminus is poorly resolved. In this study we use ring widths of living Sitka spruce (Picea sitchensis) at 350 m-elevation near a lateral moraine in the Chaix Hills to reconstruct when the adjacent ice surface rose to and receded from the growth site. Cores from 33 trees were crossdated and used to develop a tree-ring chronology spanning 1708 to 1994 CE. Correlations with regional climate data show that these trees produced wider rings when January to March of the growth year was warm and wet, and June of the growth year was warm and dry. The Chaix Hills tree-ring chronology was compared with three Sitka spruce chronologies from elsewhere along the coast and similar growth patterns found for year-to-year variability. However, the Chaix Hills chronology differs from the others with a multi-decadal growth decline from about 1870 to 1900, which we interpret as being due to the cold microclimate near the glacier surface rising to the growth site. The ice front of Yahtse-Guyot Glacier had reached the outer coast by the 1830s, and so this study shows that the up-glacier ice surface continued to thicken for another 40-70 years before onset of thinning and ice front recession during the 20^th century.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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