TREE-RING DATING OF THE GLACIAL HISTORY OF WACHUSETT INLET, GLACIER BAY NATIONAL PARK AND PRESERVE, SE ALASKA

Two interstadial, tree ring width chronologies were built of wood samples collected from a valley near the base of Mount Wordie in Wachusett Inlet in the East Arm of Glacier Bay. Seventy-five cores and sections from in situ forests and detrital logs were analyzed from 40 locations. Radiocarbon dating provides absolute age for the ring-width series which shows that trees were likely killed by a series of ice-related sedimentation events at approximately 3.3 ka and at approximately 2.5 ka. In situ trees are linked stratigraphically to the glacial advances and occur within glaciolacustrine, deltaic, glaciofluvial, and glacial diamicts. The 3.3 ka chronology spans 570 years, whereas the 2.5 ka chronology spans 280 years and document the duration of ice-free conditions before each respective glacial advance.

The two ring-width chronologies strongly cross date with our regional tree-ring-width series from Geikie Inlet and Muir Inlet in the East and West Arms respectively. Cross Dating over this broad region suggests that the two glacial expansions covered much of the Glacier Bay watershed. The added resolution of the tree-ring dating reveals ice in the West Arm expanding to the mouth of Geikie Inlet, 30 km southwest of Wachusett Inlet, killing trees there decades before those within the Mt. Wordie valley. Farther to the east and up valley approximately 15 km, Muir Inlet ice expanded several decades after upper Wachusett Inlet. The coupled use of radiocarbon dating with tree-ring-width chronologies adds decadal resolution to the glacial chronology within Glacier Bay.